††thanks: Deceased††thanks: Deceased††thanks: Deceased††thanks:
Deceased††thanks: Deceased

CDF Collaboration With visitors from] aUniversity of British Columbia,
Vancouver, BC V6T 1Z1, Canada, bIstituto Nazionale di Fisica Nucleare, Sezione
di Cagliari, 09042 Monserrato (Cagliari), Italy, cUniversity of California
Irvine, Irvine, CA 92697, USA, dInstitute of Physics, Academy of Sciences of
the Czech Republic, 182 21, Czech Republic, eCERN, CH-1211 Geneva,
Switzerland, fCornell University, Ithaca, NY 14853, USA, gUniversity of
Cyprus, Nicosia CY-1678, Cyprus, hOffice of Science, U.S. Department of
Energy, Washington, DC 20585, USA, iUniversity College Dublin, Dublin 4,
Ireland, jETH, 8092 Zürich, Switzerland, kUniversity of Fukui, Fukui City,
Fukui Prefecture, Japan 910-0017, lUniversidad Iberoamericana, Lomas de Santa
Fe, México, C.P. 01219, Distrito Federal, mUniversity of Iowa, Iowa City, IA
52242, USA, nKinki University, Higashi-Osaka City, Japan 577-8502, oKansas
State University, Manhattan, KS 66506, USA, pBrookhaven National Laboratory,
Upton, NY 11973, USA, qIstituto Nazionale di Fisica Nucleare, Sezione di
Lecce, Via Arnesano, I-73100 Lecce, Italy, rQueen Mary, University of London,
London, E1 4NS, United Kingdom, sUniversity of Melbourne, Victoria 3010,
Australia, tMuons, Inc., Batavia, IL 60510, USA, uNagasaki Institute of
Applied Science, Nagasaki 851-0193, Japan, vNational Research Nuclear
University, Moscow 115409, Russia, wNorthwestern University, Evanston, IL
60208, USA, xUniversity of Notre Dame, Notre Dame, IN 46556, USA, yUniversidad
de Oviedo, E-33007 Oviedo, Spain, zCNRS-IN2P3, Paris, F-75205 France,
aaUniversidad Tecnica Federico Santa Maria, 110v Valparaiso, Chile, bbSejong
University, Seoul 143-747, Korea, ccThe University of Jordan, Amman 11942,
Jordan, ddUniversite catholique de Louvain, 1348 Louvain-La-Neuve, Belgium,
eeUniversity of Zürich, 8006 Zürich, Switzerland, ffMassachusetts General
Hospital, Boston, MA 02114 USA, ggHarvard Medical School, Boston, MA 02114
USA, hhHampton University, Hampton, VA 23668, USA, iiLos Alamos National
Laboratory, Los Alamos, NM 87544, USA, jjUniversità degli Studi di Napoli
Federico II, I-80138 Napoli, Italy

# A novel measurement of initial-state gluon radiation in hadron collisions
using Drell-Yan events

T. Aaltonen  Division of High Energy Physics, Department of Physics,
University of Helsinki, FIN-00014, Helsinki, Finland; Helsinki Institute of
Physics, FIN-00014, Helsinki, Finland  S. Amerioll Istituto Nazionale di
Fisica Nucleare, Sezione di Padova, llUniversity of Padova, I-35131 Padova,
Italy  D. Amidei  University of Michigan, Ann Arbor, Michigan 48109, USA  A.
Anastassovw Fermi National Accelerator Laboratory, Batavia, Illinois 60510,
USA  A. Annovi  Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica
Nucleare, I-00044 Frascati, Italy  J. Antos  Comenius University, 842 48
Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice,
Slovakia  G. Apollinari  Fermi National Accelerator Laboratory, Batavia,
Illinois 60510, USA  J.A. Appel  Fermi National Accelerator Laboratory,
Batavia, Illinois 60510, USA  T. Arisawa  Waseda University, Tokyo 169, Japan
A. Artikov  Joint Institute for Nuclear Research, RU-141980 Dubna, Russia  J.
Asaadi  Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M
University, College Station, Texas 77843, USA  W. Ashmanskas  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  B. Auerbach  Argonne
National Laboratory, Argonne, Illinois 60439, USA  A. Aurisano  Mitchell
Institute for Fundamental Physics and Astronomy, Texas A&M University, College
Station, Texas 77843, USA  F. Azfar  University of Oxford, Oxford OX1 3RH,
United Kingdom  W. Badgett  Fermi National Accelerator Laboratory, Batavia,
Illinois 60510, USA  T. Bae  Center for High Energy Physics: Kyungpook
National University, Daegu 702-701, Korea; Seoul National University, Seoul
151-742, Korea; Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute
of Science and Technology Information, Daejeon 305-806, Korea; Chonnam
National University, Gwangju 500-757, Korea; Chonbuk National University,
Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750, Korea  A.
Barbaro-Galtieri  Ernest Orlando Lawrence Berkeley National Laboratory,
Berkeley, California 94720, USA  V.E. Barnes  Purdue University, West
Lafayette, Indiana 47907, USA  B.A. Barnett  The Johns Hopkins University,
Baltimore, Maryland 21218, USA  P. Barriann Istituto Nazionale di Fisica
Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale
Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  P. Bartos  Comenius University,
842 48 Bratislava, Slovakia; Institute of Experimental Physics, 040 01 Kosice,
Slovakia  M. Baucell Istituto Nazionale di Fisica Nucleare, Sezione di Padova,
llUniversity of Padova, I-35131 Padova, Italy  F. Bedeschi  Istituto Nazionale
di Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola
Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  S. Behari  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  G. Bellettinimm Istituto
Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity of
Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100
Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  J. Bellinger
University of Wisconsin-Madison, Madison, Wisconsin 53706, USA  D. Benjamin
Duke University, Durham, North Carolina 27708, USA  A. Beretvas  Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  A. Bhatti  The
Rockefeller University, New York, New York 10065, USA  K.R. Bland  Baylor
University, Waco, Texas 76798, USA  B. Blumenfeld  The Johns Hopkins
University, Baltimore, Maryland 21218, USA  A. Bocci  Duke University, Durham,
North Carolina 27708, USA  A. Bodek  University of Rochester, Rochester, New
York 14627, USA  D. Bortoletto  Purdue University, West Lafayette, Indiana
47907, USA  J. Boudreau  University of Pittsburgh, Pittsburgh, Pennsylvania
15260, USA  A. Boveia  Enrico Fermi Institute, University of Chicago, Chicago,
Illinois 60637, USA  L. Brigliadorikk Istituto Nazionale di Fisica Nucleare
Bologna, kkUniversity of Bologna, I-40127 Bologna, Italy  C. Bromberg
Michigan State University, East Lansing, Michigan 48824, USA  E. Brucken
Division of High Energy Physics, Department of Physics, University of
Helsinki, FIN-00014, Helsinki, Finland; Helsinki Institute of Physics,
FIN-00014, Helsinki, Finland  J. Budagov  Joint Institute for Nuclear
Research, RU-141980 Dubna, Russia  H.S. Budd  University of Rochester,
Rochester, New York 14627, USA  K. Burkett  Fermi National Accelerator
Laboratory, Batavia, Illinois 60510, USA  G. Busettoll Istituto Nazionale di
Fisica Nucleare, Sezione di Padova, llUniversity of Padova, I-35131 Padova,
Italy  P. Bussey  Glasgow University, Glasgow G12 8QQ, United Kingdom  P.
Buttimm Istituto Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa,
nnUniversity of Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN
Pavia, I-27100 Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  A.
Buzatu  Glasgow University, Glasgow G12 8QQ, United Kingdom  A. Calamba
Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA  S. Camarda
Institut de Fisica d’Altes Energies, ICREA, Universitat Autonoma de Barcelona,
E-08193, Bellaterra (Barcelona), Spain  M. Campanelli  University College
London, London WC1E 6BT, United Kingdom  F. Canelliee Enrico Fermi Institute,
University of Chicago, Chicago, Illinois 60637, USA  B. Carls  University of
Illinois, Urbana, Illinois 61801, USA  D. Carlsmith  University of Wisconsin-
Madison, Madison, Wisconsin 53706, USA  R. Carosi  Istituto Nazionale di
Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola
Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  S. Carrillol University of
Florida, Gainesville, Florida 32611, USA  B. Casalj Instituto de Fisica de
Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain  M. Casarsa
Istituto Nazionale di Fisica Nucleare Trieste, ssGruppo Collegato di Udine,
ttUniversity of Udine, I-33100 Udine, Italy, uuUniversity of Trieste, I-34127
Trieste, Italy  A. Castrokk Istituto Nazionale di Fisica Nucleare Bologna,
kkUniversity of Bologna, I-40127 Bologna, Italy  P. Catastini  Harvard
University, Cambridge, Massachusetts 02138, USA  D. Cauzsstt Istituto
Nazionale di Fisica Nucleare Trieste, ssGruppo Collegato di Udine,
ttUniversity of Udine, I-33100 Udine, Italy, uuUniversity of Trieste, I-34127
Trieste, Italy  V. Cavaliere  University of Illinois, Urbana, Illinois 61801,
USA  A. Cerrie Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley,
California 94720, USA  L. Cerritor University College London, London WC1E 6BT,
United Kingdom  Y.C. Chen  Institute of Physics, Academia Sinica, Taipei,
Taiwan 11529, Republic of China  M. Chertok  University of California, Davis,
Davis, California 95616, USA  G. Chiarelli  Istituto Nazionale di Fisica
Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale
Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  G. Chlachidze  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  K. Cho  Center for High
Energy Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul
National University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon
440-746, Korea; Korea Institute of Science and Technology Information, Daejeon
305-806, Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk
National University, Jeonju 561-756, Korea; Ewha Womans University, Seoul,
120-750, Korea  D. Chokheli  Joint Institute for Nuclear Research, RU-141980
Dubna, Russia  A. Clark  University of Geneva, CH-1211 Geneva 4, Switzerland
C. Clarke  Wayne State University, Detroit, Michigan 48201, USA  M.E. Convery
Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA  J. Conway
University of California, Davis, Davis, California 95616, USA  M. Corboz Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  M. Cordelli
Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare,
I-00044 Frascati, Italy  C.A. Cox  University of California, Davis, Davis,
California 95616, USA  D.J. Cox  University of California, Davis, Davis,
California 95616, USA  M. Cremonesi  Istituto Nazionale di Fisica Nucleare
Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale Superiore,
I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy, qqUniversity of
Pavia, I-27100 Pavia, Italy  D. Cruz  Mitchell Institute for Fundamental
Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA
J. Cuevasy Instituto de Fisica de Cantabria, CSIC-University of Cantabria,
39005 Santander, Spain  R. Culbertson  Fermi National Accelerator Laboratory,
Batavia, Illinois 60510, USA  N. d’Ascenzov Fermi National Accelerator
Laboratory, Batavia, Illinois 60510, USA  M. Dattahh Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  P. de Barbaro
University of Rochester, Rochester, New York 14627, USA  L. Demortier  The
Rockefeller University, New York, New York 10065, USA  M. Deninno  Istituto
Nazionale di Fisica Nucleare Bologna, kkUniversity of Bologna, I-40127
Bologna, Italy  M. D’Erricoll Istituto Nazionale di Fisica Nucleare, Sezione
di Padova, llUniversity of Padova, I-35131 Padova, Italy  F. Devoto  Division
of High Energy Physics, Department of Physics, University of Helsinki,
FIN-00014, Helsinki, Finland; Helsinki Institute of Physics, FIN-00014,
Helsinki, Finland  A. Di Cantomm Istituto Nazionale di Fisica Nucleare Pisa,
mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale Superiore,
I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy, qqUniversity of
Pavia, I-27100 Pavia, Italy  B. Di Ruzzap Fermi National Accelerator
Laboratory, Batavia, Illinois 60510, USA  J.R. Dittmann  Baylor University,
Waco, Texas 76798, USA  S. Donatimm Istituto Nazionale di Fisica Nucleare
Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale Superiore,
I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy, qqUniversity of
Pavia, I-27100 Pavia, Italy  M. D’Onofrio  University of Liverpool, Liverpool
L69 7ZE, United Kingdom  M. Dorigouu Istituto Nazionale di Fisica Nucleare
Trieste, ssGruppo Collegato di Udine, ttUniversity of Udine, I-33100 Udine,
Italy, uuUniversity of Trieste, I-34127 Trieste, Italy  A. Driuttisstt
Istituto Nazionale di Fisica Nucleare Trieste, ssGruppo Collegato di Udine,
ttUniversity of Udine, I-33100 Udine, Italy, uuUniversity of Trieste, I-34127
Trieste, Italy  K. Ebina  Waseda University, Tokyo 169, Japan  R. Edgar
University of Michigan, Ann Arbor, Michigan 48109, USA  A. Elagin  Enrico
Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA  R.
Erbacher  University of California, Davis, Davis, California 95616, USA  S.
Errede  University of Illinois, Urbana, Illinois 61801, USA  B. Esham
University of Illinois, Urbana, Illinois 61801, USA  S. Farrington  University
of Oxford, Oxford OX1 3RH, United Kingdom  J.P. Fernández Ramos  Centro de
Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid,
Spain  R. Field  University of Florida, Gainesville, Florida 32611, USA  G.
Flanagant Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
R. Forrest  University of California, Davis, Davis, California 95616, USA  M.
Franklin  Harvard University, Cambridge, Massachusetts 02138, USA  J.C.
Freeman  Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
H. Frisch  Enrico Fermi Institute, University of Chicago, Chicago, Illinois
60637, USA  Y. Funakoshi  Waseda University, Tokyo 169, Japan  C. Gallonimm
Istituto Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity
of Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia,
I-27100 Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  A.F.
Garfinkel  Purdue University, West Lafayette, Indiana 47907, USA  P. Garosinn
Istituto Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity
of Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia,
I-27100 Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  H.
Gerberich  University of Illinois, Urbana, Illinois 61801, USA  E. Gerchtein
Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA  S. Giagu
Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1, rrSapienza
Università di Roma, I-00185 Roma, Italy  V. Giakoumopoulou  University of
Athens, 157 71 Athens, Greece  K. Gibson  University of Pittsburgh,
Pittsburgh, Pennsylvania 15260, USA  C.M. Ginsburg  Fermi National Accelerator
Laboratory, Batavia, Illinois 60510, USA  N. Giokaris  University of Athens,
157 71 Athens, Greece  P. Giromini  Laboratori Nazionali di Frascati, Istituto
Nazionale di Fisica Nucleare, I-00044 Frascati, Italy  V. Glagolev  Joint
Institute for Nuclear Research, RU-141980 Dubna, Russia  D. Glenzinski  Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  M. Gold
University of New Mexico, Albuquerque, New Mexico 87131, USA  D. Goldin
Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M
University, College Station, Texas 77843, USA  A. Golossanov  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  G. Gomez  Instituto de
Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain  G.
Gomez-Ceballos  Massachusetts Institute of Technology, Cambridge,
Massachusetts 02139, USA  M. Goncharov  Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, USA  O. González López  Centro de
Investigaciones Energeticas Medioambientales y Tecnologicas, E-28040 Madrid,
Spain  I. Gorelov  University of New Mexico, Albuquerque, New Mexico 87131,
USA  A.T. Goshaw  Duke University, Durham, North Carolina 27708, USA  K.
Goulianos  The Rockefeller University, New York, New York 10065, USA  E.
Gramellini  Istituto Nazionale di Fisica Nucleare Bologna, kkUniversity of
Bologna, I-40127 Bologna, Italy  C. Grosso-Pilcher  Enrico Fermi Institute,
University of Chicago, Chicago, Illinois 60637, USA  J. Guimaraes da Costa
Harvard University, Cambridge, Massachusetts 02138, USA  S.R. Hahn  Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  J.Y. Han
University of Rochester, Rochester, New York 14627, USA  F. Happacher
Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare,
I-00044 Frascati, Italy  K. Hara  University of Tsukuba, Tsukuba, Ibaraki 305,
Japan  M. Hare  Tufts University, Medford, Massachusetts 02155, USA  R.F. Harr
Wayne State University, Detroit, Michigan 48201, USA  T. Harrington-Taberm
Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA  K.
Hatakeyama  Baylor University, Waco, Texas 76798, USA  C. Hays  University of
Oxford, Oxford OX1 3RH, United Kingdom  J. Heinrich  University of
Pennsylvania, Philadelphia, Pennsylvania 19104, USA  M. Herndon  University of
Wisconsin-Madison, Madison, Wisconsin 53706, USA  A. Hocker  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  Z. Hongw Mitchell
Institute for Fundamental Physics and Astronomy, Texas A&M University, College
Station, Texas 77843, USA  W. Hopkinsf Fermi National Accelerator Laboratory,
Batavia, Illinois 60510, USA  S. Hou  Institute of Physics, Academia Sinica,
Taipei, Taiwan 11529, Republic of China  R.E. Hughes  The Ohio State
University, Columbus, Ohio 43210, USA  U. Husemann  Yale University, New
Haven, Connecticut 06520, USA  M. Husseincc Michigan State University, East
Lansing, Michigan 48824, USA  J. Huston  Michigan State University, East
Lansing, Michigan 48824, USA  G. Introzzippqq Istituto Nazionale di Fisica
Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale
Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  M. Iorirr Istituto Nazionale di
Fisica Nucleare, Sezione di Roma 1, rrSapienza Università di Roma, I-00185
Roma, Italy  A. Ivanovo University of California, Davis, Davis, California
95616, USA  E. James  Fermi National Accelerator Laboratory, Batavia, Illinois
60510, USA  D. Jang  Carnegie Mellon University, Pittsburgh, Pennsylvania
15213, USA  B. Jayatilaka  Fermi National Accelerator Laboratory, Batavia,
Illinois 60510, USA  E.J. Jeon  Center for High Energy Physics: Kyungpook
National University, Daegu 702-701, Korea; Seoul National University, Seoul
151-742, Korea; Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute
of Science and Technology Information, Daejeon 305-806, Korea; Chonnam
National University, Gwangju 500-757, Korea; Chonbuk National University,
Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750, Korea  S.
Jindariani  Fermi National Accelerator Laboratory, Batavia, Illinois 60510,
USA  M. Jones  Purdue University, West Lafayette, Indiana 47907, USA  K.K. Joo
Center for High Energy Physics: Kyungpook National University, Daegu 702-701,
Korea; Seoul National University, Seoul 151-742, Korea; Sungkyunkwan
University, Suwon 440-746, Korea; Korea Institute of Science and Technology
Information, Daejeon 305-806, Korea; Chonnam National University, Gwangju
500-757, Korea; Chonbuk National University, Jeonju 561-756, Korea; Ewha
Womans University, Seoul, 120-750, Korea  S.Y. Jun  Carnegie Mellon
University, Pittsburgh, Pennsylvania 15213, USA  T.R. Junk  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  M. Kambeitz  Institut
für Experimentelle Kernphysik, Karlsruhe Institute of Technology, D-76131
Karlsruhe, Germany  T. Kamon  Center for High Energy Physics: Kyungpook
National University, Daegu 702-701, Korea; Seoul National University, Seoul
151-742, Korea; Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute
of Science and Technology Information, Daejeon 305-806, Korea; Chonnam
National University, Gwangju 500-757, Korea; Chonbuk National University,
Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750, Korea  Mitchell
Institute for Fundamental Physics and Astronomy, Texas A&M University, College
Station, Texas 77843, USA  P.E. Karchin  Wayne State University, Detroit,
Michigan 48201, USA  A. Kasmi  Baylor University, Waco, Texas 76798, USA  Y.
Katon Osaka City University, Osaka 558-8585, Japan  W. Ketchumii Enrico Fermi
Institute, University of Chicago, Chicago, Illinois 60637, USA  J. Keung
University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA  B.
Kilminsteree Fermi National Accelerator Laboratory, Batavia, Illinois 60510,
USA  D.H. Kim  Center for High Energy Physics: Kyungpook National University,
Daegu 702-701, Korea; Seoul National University, Seoul 151-742, Korea;
Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute of Science and
Technology Information, Daejeon 305-806, Korea; Chonnam National University,
Gwangju 500-757, Korea; Chonbuk National University, Jeonju 561-756, Korea;
Ewha Womans University, Seoul, 120-750, Korea  H.S. Kimbb Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  J.E. Kim  Center for
High Energy Physics: Kyungpook National University, Daegu 702-701, Korea;
Seoul National University, Seoul 151-742, Korea; Sungkyunkwan University,
Suwon 440-746, Korea; Korea Institute of Science and Technology Information,
Daejeon 305-806, Korea; Chonnam National University, Gwangju 500-757, Korea;
Chonbuk National University, Jeonju 561-756, Korea; Ewha Womans University,
Seoul, 120-750, Korea  M.J. Kim  Laboratori Nazionali di Frascati, Istituto
Nazionale di Fisica Nucleare, I-00044 Frascati, Italy  S.H. Kim  University of
Tsukuba, Tsukuba, Ibaraki 305, Japan  S.B. Kim  Center for High Energy
Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul National
University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746,
Korea; Korea Institute of Science and Technology Information, Daejeon 305-806,
Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk National
University, Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750,
Korea  Y.J. Kim  Center for High Energy Physics: Kyungpook National
University, Daegu 702-701, Korea; Seoul National University, Seoul 151-742,
Korea; Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute of
Science and Technology Information, Daejeon 305-806, Korea; Chonnam National
University, Gwangju 500-757, Korea; Chonbuk National University, Jeonju
561-756, Korea; Ewha Womans University, Seoul, 120-750, Korea  Y.K. Kim
Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA
N. Kimura  Waseda University, Tokyo 169, Japan  M. Kirby  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  K. Kondo  Waseda
University, Tokyo 169, Japan  D.J. Kong  Center for High Energy Physics:
Kyungpook National University, Daegu 702-701, Korea; Seoul National
University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746,
Korea; Korea Institute of Science and Technology Information, Daejeon 305-806,
Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk National
University, Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750,
Korea  J. Konigsberg  University of Florida, Gainesville, Florida 32611, USA
A.V. Kotwal  Duke University, Durham, North Carolina 27708, USA  M. Kreps
Institut für Experimentelle Kernphysik, Karlsruhe Institute of Technology,
D-76131 Karlsruhe, Germany  J. Kroll  University of Pennsylvania,
Philadelphia, Pennsylvania 19104, USA  M. Kruse  Duke University, Durham,
North Carolina 27708, USA  T. Kuhr  Institut für Experimentelle Kernphysik,
Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany  M. Kurata
University of Tsukuba, Tsukuba, Ibaraki 305, Japan  A.T. Laasanen  Purdue
University, West Lafayette, Indiana 47907, USA  S. Lammel  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  M. Lancaster  University
College London, London WC1E 6BT, United Kingdom  K. Lannonx The Ohio State
University, Columbus, Ohio 43210, USA  G. Latinonn Istituto Nazionale di
Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola
Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  H.S. Lee  Center for High Energy
Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul National
University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746,
Korea; Korea Institute of Science and Technology Information, Daejeon 305-806,
Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk National
University, Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750,
Korea  J.S. Lee  Center for High Energy Physics: Kyungpook National
University, Daegu 702-701, Korea; Seoul National University, Seoul 151-742,
Korea; Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute of
Science and Technology Information, Daejeon 305-806, Korea; Chonnam National
University, Gwangju 500-757, Korea; Chonbuk National University, Jeonju
561-756, Korea; Ewha Womans University, Seoul, 120-750, Korea  S. Leo
University of Illinois, Urbana, Illinois 61801, USA  S. Leone  Istituto
Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity of
Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100
Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  J.D. Lewis  Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  A. Limosanis
Duke University, Durham, North Carolina 27708, USA  E. Lipeles  University of
Pennsylvania, Philadelphia, Pennsylvania 19104, USA  A. Listera University of
Geneva, CH-1211 Geneva 4, Switzerland  Q. Liu  Purdue University, West
Lafayette, Indiana 47907, USA  T. Liu  Fermi National Accelerator Laboratory,
Batavia, Illinois 60510, USA  S. Lockwitz  Yale University, New Haven,
Connecticut 06520, USA  A. Loginov  Yale University, New Haven, Connecticut
06520, USA  D. Lucchesill Istituto Nazionale di Fisica Nucleare, Sezione di
Padova, llUniversity of Padova, I-35131 Padova, Italy  A. Lucà  Laboratori
Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044
Frascati, Italy  Fermi National Accelerator Laboratory, Batavia, Illinois
60510, USA  J. Lueck  Institut für Experimentelle Kernphysik, Karlsruhe
Institute of Technology, D-76131 Karlsruhe, Germany  P. Lujan  Ernest Orlando
Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA  P.
Lukens  Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
G. Lungu  The Rockefeller University, New York, New York 10065, USA  J. Lys
Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California
94720, USA  R. Lysakd Comenius University, 842 48 Bratislava, Slovakia;
Institute of Experimental Physics, 040 01 Kosice, Slovakia  R. Madrak  Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  P. Maestronn
Istituto Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity
of Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia,
I-27100 Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  S. Malik
The Rockefeller University, New York, New York 10065, USA  G. Mancab
University of Liverpool, Liverpool L69 7ZE, United Kingdom  A. Manousakis-
Katsikakis  University of Athens, 157 71 Athens, Greece  L. Marchesejj
Istituto Nazionale di Fisica Nucleare Bologna, kkUniversity of Bologna,
I-40127 Bologna, Italy  F. Margaroli  Istituto Nazionale di Fisica Nucleare,
Sezione di Roma 1, rrSapienza Università di Roma, I-00185 Roma, Italy  P.
Marinooo Istituto Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa,
nnUniversity of Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN
Pavia, I-27100 Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  K.
Matera  University of Illinois, Urbana, Illinois 61801, USA  M.E. Mattson
Wayne State University, Detroit, Michigan 48201, USA  A. Mazzacane  Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  P. Mazzanti
Istituto Nazionale di Fisica Nucleare Bologna, kkUniversity of Bologna,
I-40127 Bologna, Italy  R. McNultyi University of Liverpool, Liverpool L69
7ZE, United Kingdom  A. Mehta  University of Liverpool, Liverpool L69 7ZE,
United Kingdom  P. Mehtala  Division of High Energy Physics, Department of
Physics, University of Helsinki, FIN-00014, Helsinki, Finland; Helsinki
Institute of Physics, FIN-00014, Helsinki, Finland  C. Mesropian  The
Rockefeller University, New York, New York 10065, USA  T. Miao  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  E. Michielinll Istituto
Nazionale di Fisica Nucleare, Sezione di Padova, llUniversity of Padova,
I-35131 Padova, Italy  D. Mietlicki  University of Michigan, Ann Arbor,
Michigan 48109, USA  A. Mitra  Institute of Physics, Academia Sinica, Taipei,
Taiwan 11529, Republic of China  H. Miyake  University of Tsukuba, Tsukuba,
Ibaraki 305, Japan  S. Moed  Fermi National Accelerator Laboratory, Batavia,
Illinois 60510, USA  N. Moggi  Istituto Nazionale di Fisica Nucleare Bologna,
kkUniversity of Bologna, I-40127 Bologna, Italy  C.S. Moon  Center for High
Energy Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul
National University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon
440-746, Korea; Korea Institute of Science and Technology Information, Daejeon
305-806, Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk
National University, Jeonju 561-756, Korea; Ewha Womans University, Seoul,
120-750, Korea  R. Mooreffgg Fermi National Accelerator Laboratory, Batavia,
Illinois 60510, USA  M.J. Morellooo Istituto Nazionale di Fisica Nucleare
Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale Superiore,
I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy, qqUniversity of
Pavia, I-27100 Pavia, Italy  A. Mukherjee  Fermi National Accelerator
Laboratory, Batavia, Illinois 60510, USA  Th. Muller  Institut für
Experimentelle Kernphysik, Karlsruhe Institute of Technology, D-76131
Karlsruhe, Germany  P. Murat  Fermi National Accelerator Laboratory, Batavia,
Illinois 60510, USA  M. Mussinikk Istituto Nazionale di Fisica Nucleare
Bologna, kkUniversity of Bologna, I-40127 Bologna, Italy  J. Nachtmanm Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  Y. Nagai
University of Tsukuba, Tsukuba, Ibaraki 305, Japan  J. Naganoma  Waseda
University, Tokyo 169, Japan  I. Nakano  Okayama University, Okayama 700-8530,
Japan  A. Napier  Tufts University, Medford, Massachusetts 02155, USA  J. Nett
Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M
University, College Station, Texas 77843, USA  T. Nigmanov  University of
Pittsburgh, Pittsburgh, Pennsylvania 15260, USA  L. Nodulman  Argonne National
Laboratory, Argonne, Illinois 60439, USA  S.Y. Noh  Center for High Energy
Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul National
University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746,
Korea; Korea Institute of Science and Technology Information, Daejeon 305-806,
Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk National
University, Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750,
Korea  O. Norniella  University of Illinois, Urbana, Illinois 61801, USA  L.
Oakes  University of Oxford, Oxford OX1 3RH, United Kingdom  S.H. Oh  Duke
University, Durham, North Carolina 27708, USA  Y.D. Oh  Center for High Energy
Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul National
University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746,
Korea; Korea Institute of Science and Technology Information, Daejeon 305-806,
Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk National
University, Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750,
Korea  T. Okusawa  Osaka City University, Osaka 558-8585, Japan  R. Orava
Division of High Energy Physics, Department of Physics, University of
Helsinki, FIN-00014, Helsinki, Finland; Helsinki Institute of Physics,
FIN-00014, Helsinki, Finland  L. Ortolan  Institut de Fisica d’Altes Energies,
ICREA, Universitat Autonoma de Barcelona, E-08193, Bellaterra (Barcelona),
Spain  C. Pagliarone  Istituto Nazionale di Fisica Nucleare Trieste, ssGruppo
Collegato di Udine, ttUniversity of Udine, I-33100 Udine, Italy, uuUniversity
of Trieste, I-34127 Trieste, Italy  E. Palenciae Instituto de Fisica de
Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain  P. Palni
University of New Mexico, Albuquerque, New Mexico 87131, USA  V. Papadimitriou
Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA  W. Parker
University of Wisconsin-Madison, Madison, Wisconsin 53706, USA  G.
Paulettasstt Istituto Nazionale di Fisica Nucleare Trieste, ssGruppo Collegato
di Udine, ttUniversity of Udine, I-33100 Udine, Italy, uuUniversity of
Trieste, I-34127 Trieste, Italy  M. Paulini  Carnegie Mellon University,
Pittsburgh, Pennsylvania 15213, USA  C. Paus  Massachusetts Institute of
Technology, Cambridge, Massachusetts 02139, USA  T.J. Phillips  Duke
University, Durham, North Carolina 27708, USA  G. Piacentinoq Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  E. Pianori  University
of Pennsylvania, Philadelphia, Pennsylvania 19104, USA  J. Pilot  University
of California, Davis, Davis, California 95616, USA  K. Pitts  University of
Illinois, Urbana, Illinois 61801, USA  C. Plager  University of California,
Los Angeles, Los Angeles, California 90024, USA  L. Pondrom  University of
Wisconsin-Madison, Madison, Wisconsin 53706, USA  S. Poprockif Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  K. Potamianos  Ernest
Orlando Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
A. Pranko  Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley,
California 94720, USA  F. Prokoshinaa Joint Institute for Nuclear Research,
RU-141980 Dubna, Russia  F. Ptohosg Laboratori Nazionali di Frascati, Istituto
Nazionale di Fisica Nucleare, I-00044 Frascati, Italy  G. Punzimm Istituto
Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity of
Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100
Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  I. Redondo
Fernández  Centro de Investigaciones Energeticas Medioambientales y
Tecnologicas, E-28040 Madrid, Spain  P. Renton  University of Oxford, Oxford
OX1 3RH, United Kingdom  M. Rescigno  Istituto Nazionale di Fisica Nucleare,
Sezione di Roma 1, rrSapienza Università di Roma, I-00185 Roma, Italy  F.
Rimondi  Istituto Nazionale di Fisica Nucleare Bologna, kkUniversity of
Bologna, I-40127 Bologna, Italy  L. Ristori  Istituto Nazionale di Fisica
Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale
Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  Fermi National Accelerator
Laboratory, Batavia, Illinois 60510, USA  A. Robson  Glasgow University,
Glasgow G12 8QQ, United Kingdom  T. Rodriguez  University of Pennsylvania,
Philadelphia, Pennsylvania 19104, USA  S. Rollih Tufts University, Medford,
Massachusetts 02155, USA  M. Ronzanimm Istituto Nazionale di Fisica Nucleare
Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale Superiore,
I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy, qqUniversity of
Pavia, I-27100 Pavia, Italy  R. Roser  Fermi National Accelerator Laboratory,
Batavia, Illinois 60510, USA  J.L. Rosner  Enrico Fermi Institute, University
of Chicago, Chicago, Illinois 60637, USA  F. Ruffininn Istituto Nazionale di
Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola
Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  A. Ruiz  Instituto de Fisica de
Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain  J. Russ
Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA  V. Rusu
Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA  W.K.
Sakumoto  University of Rochester, Rochester, New York 14627, USA  Y. Sakurai
Waseda University, Tokyo 169, Japan  L. Santisstt Istituto Nazionale di Fisica
Nucleare Trieste, ssGruppo Collegato di Udine, ttUniversity of Udine, I-33100
Udine, Italy, uuUniversity of Trieste, I-34127 Trieste, Italy  K. Sato
University of Tsukuba, Tsukuba, Ibaraki 305, Japan  V. Savelievv Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  A. Savoy-
Navarroz Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
P. Schlabach  Fermi National Accelerator Laboratory, Batavia, Illinois 60510,
USA  E.E. Schmidt  Fermi National Accelerator Laboratory, Batavia, Illinois
60510, USA  T. Schwarz  University of Michigan, Ann Arbor, Michigan 48109, USA
L. Scodellaro  Instituto de Fisica de Cantabria, CSIC-University of Cantabria,
39005 Santander, Spain  F. Scuri  Istituto Nazionale di Fisica Nucleare Pisa,
mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale Superiore,
I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy, qqUniversity of
Pavia, I-27100 Pavia, Italy  S. Seidel  University of New Mexico, Albuquerque,
New Mexico 87131, USA  Y. Seiya  Osaka City University, Osaka 558-8585, Japan
A. Semenov  Joint Institute for Nuclear Research, RU-141980 Dubna, Russia  H.
Seo  Center for High Energy Physics: Kyungpook National University, Daegu
702-701, Korea; Seoul National University, Seoul 151-742, Korea; Sungkyunkwan
University, Suwon 440-746, Korea; Korea Institute of Science and Technology
Information, Daejeon 305-806, Korea; Chonnam National University, Gwangju
500-757, Korea; Chonbuk National University, Jeonju 561-756, Korea; Ewha
Womans University, Seoul, 120-750, Korea  F. Sforzamm Istituto Nazionale di
Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity of Siena, ooScuola
Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy,
qqUniversity of Pavia, I-27100 Pavia, Italy  S.Z. Shalhout  University of
California, Davis, Davis, California 95616, USA  T. Shears  University of
Liverpool, Liverpool L69 7ZE, United Kingdom  P.F. Shepard  University of
Pittsburgh, Pittsburgh, Pennsylvania 15260, USA  M. Shimojimau University of
Tsukuba, Tsukuba, Ibaraki 305, Japan  M. Shochet  Enrico Fermi Institute,
University of Chicago, Chicago, Illinois 60637, USA  I. Shreyber-Tecker
Institution for Theoretical and Experimental Physics, ITEP, Moscow 117259,
Russia  A. Simonenko  Joint Institute for Nuclear Research, RU-141980 Dubna,
Russia  K. Sliwa  Tufts University, Medford, Massachusetts 02155, USA  J.R.
Smith  University of California, Davis, Davis, California 95616, USA  F.D.
Snider  Fermi National Accelerator Laboratory, Batavia, Illinois 60510, USA
H. Song  University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA  V.
Sorin  Institut de Fisica d’Altes Energies, ICREA, Universitat Autonoma de
Barcelona, E-08193, Bellaterra (Barcelona), Spain  R. St. Denis  Glasgow
University, Glasgow G12 8QQ, United Kingdom  M. Stancari  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  D. Stentzw Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  J. Strologas
University of New Mexico, Albuquerque, New Mexico 87131, USA  Y. Sudo
University of Tsukuba, Tsukuba, Ibaraki 305, Japan  A. Sukhanov  Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  I. Suslov
Joint Institute for Nuclear Research, RU-141980 Dubna, Russia  K. Takemasa
University of Tsukuba, Tsukuba, Ibaraki 305, Japan  Y. Takeuchi  University of
Tsukuba, Tsukuba, Ibaraki 305, Japan  J. Tang  Enrico Fermi Institute,
University of Chicago, Chicago, Illinois 60637, USA  M. Tecchio  University of
Michigan, Ann Arbor, Michigan 48109, USA  P.K. Teng  Institute of Physics,
Academia Sinica, Taipei, Taiwan 11529, Republic of China  J. Thomf Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  E. Thomson
University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA  V. Thukral
Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M
University, College Station, Texas 77843, USA  D. Toback  Mitchell Institute
for Fundamental Physics and Astronomy, Texas A&M University, College Station,
Texas 77843, USA  S. Tokar  Comenius University, 842 48 Bratislava, Slovakia;
Institute of Experimental Physics, 040 01 Kosice, Slovakia  K. Tollefson
Michigan State University, East Lansing, Michigan 48824, USA  T. Tomura
University of Tsukuba, Tsukuba, Ibaraki 305, Japan  D. Tonellie Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  S. Torre  Laboratori
Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, I-00044
Frascati, Italy  D. Torretta  Fermi National Accelerator Laboratory, Batavia,
Illinois 60510, USA  P. Totaro  Istituto Nazionale di Fisica Nucleare, Sezione
di Padova, llUniversity of Padova, I-35131 Padova, Italy  M. Trovatooo
Istituto Nazionale di Fisica Nucleare Pisa, mmUniversity of Pisa, nnUniversity
of Siena, ooScuola Normale Superiore, I-56127 Pisa, Italy, ppINFN Pavia,
I-27100 Pavia, Italy, qqUniversity of Pavia, I-27100 Pavia, Italy  F. Ukegawa
University of Tsukuba, Tsukuba, Ibaraki 305, Japan  S. Uozumi  Center for High
Energy Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul
National University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon
440-746, Korea; Korea Institute of Science and Technology Information, Daejeon
305-806, Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk
National University, Jeonju 561-756, Korea; Ewha Womans University, Seoul,
120-750, Korea  F. Vázquezl University of Florida, Gainesville, Florida 32611,
USA  G. Velev  Fermi National Accelerator Laboratory, Batavia, Illinois 60510,
USA  C. Vellidis  Fermi National Accelerator Laboratory, Batavia, Illinois
60510, USA  C. Vernierioo Istituto Nazionale di Fisica Nucleare Pisa,
mmUniversity of Pisa, nnUniversity of Siena, ooScuola Normale Superiore,
I-56127 Pisa, Italy, ppINFN Pavia, I-27100 Pavia, Italy, qqUniversity of
Pavia, I-27100 Pavia, Italy  M. Vidal  Purdue University, West Lafayette,
Indiana 47907, USA  R. Vilar  Instituto de Fisica de Cantabria, CSIC-
University of Cantabria, 39005 Santander, Spain  J. Vizándd Instituto de
Fisica de Cantabria, CSIC-University of Cantabria, 39005 Santander, Spain  M.
Vogel  University of New Mexico, Albuquerque, New Mexico 87131, USA  G. Volpi
Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare,
I-00044 Frascati, Italy  P. Wagner  University of Pennsylvania, Philadelphia,
Pennsylvania 19104, USA  R. Wallnyj Fermi National Accelerator Laboratory,
Batavia, Illinois 60510, USA  S.M. Wang  Institute of Physics, Academia
Sinica, Taipei, Taiwan 11529, Republic of China  D. Waters  University College
London, London WC1E 6BT, United Kingdom  W.C. Wester III  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  D. Whitesonc University
of Pennsylvania, Philadelphia, Pennsylvania 19104, USA  A.B. Wicklund  Argonne
National Laboratory, Argonne, Illinois 60439, USA  S. Wilbur  University of
California, Davis, Davis, California 95616, USA  H.H. Williams  University of
Pennsylvania, Philadelphia, Pennsylvania 19104, USA  J.S. Wilson  University
of Michigan, Ann Arbor, Michigan 48109, USA  P. Wilson  Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  B.L. Winer  The Ohio
State University, Columbus, Ohio 43210, USA  P. Wittichf Fermi National
Accelerator Laboratory, Batavia, Illinois 60510, USA  S. Wolbers  Fermi
National Accelerator Laboratory, Batavia, Illinois 60510, USA  H. Wolfmeister
The Ohio State University, Columbus, Ohio 43210, USA  T. Wright  University of
Michigan, Ann Arbor, Michigan 48109, USA  X. Wu  University of Geneva, CH-1211
Geneva 4, Switzerland  Z. Wu  Baylor University, Waco, Texas 76798, USA  K.
Yamamoto  Osaka City University, Osaka 558-8585, Japan  D. Yamato  Osaka City
University, Osaka 558-8585, Japan  T. Yang  Fermi National Accelerator
Laboratory, Batavia, Illinois 60510, USA  U.K. Yang  Center for High Energy
Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul National
University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746,
Korea; Korea Institute of Science and Technology Information, Daejeon 305-806,
Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk National
University, Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750,
Korea  Y.C. Yang  Center for High Energy Physics: Kyungpook National
University, Daegu 702-701, Korea; Seoul National University, Seoul 151-742,
Korea; Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute of
Science and Technology Information, Daejeon 305-806, Korea; Chonnam National
University, Gwangju 500-757, Korea; Chonbuk National University, Jeonju
561-756, Korea; Ewha Womans University, Seoul, 120-750, Korea  W.-M. Yao
Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, California
94720, USA  G.P. Yeh  Fermi National Accelerator Laboratory, Batavia, Illinois
60510, USA  K. Yim Fermi National Accelerator Laboratory, Batavia, Illinois
60510, USA  J. Yoh  Fermi National Accelerator Laboratory, Batavia, Illinois
60510, USA  K. Yorita  Waseda University, Tokyo 169, Japan  T. Yoshidak Osaka
City University, Osaka 558-8585, Japan  G.B. Yu  Center for High Energy
Physics: Kyungpook National University, Daegu 702-701, Korea; Seoul National
University, Seoul 151-742, Korea; Sungkyunkwan University, Suwon 440-746,
Korea; Korea Institute of Science and Technology Information, Daejeon 305-806,
Korea; Chonnam National University, Gwangju 500-757, Korea; Chonbuk National
University, Jeonju 561-756, Korea; Ewha Womans University, Seoul, 120-750,
Korea  I. Yu  Center for High Energy Physics: Kyungpook National University,
Daegu 702-701, Korea; Seoul National University, Seoul 151-742, Korea;
Sungkyunkwan University, Suwon 440-746, Korea; Korea Institute of Science and
Technology Information, Daejeon 305-806, Korea; Chonnam National University,
Gwangju 500-757, Korea; Chonbuk National University, Jeonju 561-756, Korea;
Ewha Womans University, Seoul, 120-750, Korea  A.M. Zanetti  Istituto
Nazionale di Fisica Nucleare Trieste, ssGruppo Collegato di Udine,
ttUniversity of Udine, I-33100 Udine, Italy, uuUniversity of Trieste, I-34127
Trieste, Italy  Y. Zeng  Duke University, Durham, North Carolina 27708, USA
C. Zhou  Duke University, Durham, North Carolina 27708, USA  S. Zucchellikk
Istituto Nazionale di Fisica Nucleare Bologna, kkUniversity of Bologna,
I-40127 Bologna, Italy  [

(Received: date / Accepted: date)

###### Abstract

A study of initial-state gluon radiation (ISR) in hadron collisions is
presented using Drell-Yan (DY) events produced in proton-antiproton collisions
by the Tevatron collider at a center-of-mass energy of 1.96 TeV. This paper
adopts a novel approach which uses the mean value of the $Z/\gamma^{*}$
transverse momentum $\langle p_{T}^{\mathrm{DY}}\rangle$ in DY events as a
powerful observable to characterize the effect of ISR. In a data sample
corresponding to an integrated luminosity of 9.4 ${\mathrm{fb^{-1}}}$
collected with the CDF II detector, ${\langle p_{T}^{\mathrm{DY}}\rangle}$ is
measured as a function of the $Z/\gamma^{*}$ invariant mass. It is found that
these two observables have a dependence, ${\langle
p_{T}^{\mathrm{DY}}\rangle}=-8+2.2\ln{{m_{\mathrm{DY}}^{2}}}~{}[{\rm{GeV}/\it{c}}]$,
where $m_{\mathrm{DY}}$ is the value of the $Z/\gamma^{*}$ mass measured in
units of ${{\rm GeV}/c^{2}}$. This linear dependence is observed for the first
time in this analysis. It may be exploited to model the effect of ISR and
constrain its impact in other processes.

First keyword and Second keyword and More

##  I Introduction

Since the discovery of the Higgs boson [1, 2] in elementary particle physics,
the search for physics beyond the Standard Model (SM) has become the main
focus of attention. To identify small deviations from the SM expectations due
to beyond the SM (BSM) physics, a precise understanding of the SM processes is
required. At hadron colliders SM interactions are commonly accompanied by
clusters of final-state hadrons (jets) generated from initial-state gluon
radiation (ISR). A large fraction of these hadrons have low transverse
momemtum (${p_{T}}$) and are difficult to simulate and measure correctly. An
accurate modeling of ISR is essential in BSM searches at the LHC, since many
relevant models of BSM physics predict the production of undetectable
particles (such as those expected from dark-matter candidates) whose presence
can be inferred by triggering on single isolated jets produced by ISR. A
detailed understanding of ISR effects would also benefit a precise measurement
of the top-quark mass by enabling accurate modeling of the top-quark
transverse momentum distribution.

In hadron collisions, quantum-chromodynamics (QCD) gluon emissions from the
interacting partons are conventionally classified into two categories: hard
and soft/collinear emissions. The hard QCD emissions are approximately
described by perturbative QCD [3]. The soft/collinear QCD emissions are mostly
non-perturbative in nature and they are absorbed into the parton distribution
functions (PDFs). Parton-shower algorithms have been developed to approximate
the physics of the non-perturbative emissions using the DGLAP equations [4, 5,
6, 7]. The algorithms simulate the general features of non-perturbative QCD,
but their accuracy may be insufficient for high-precision analyses [8] or some
BSM particle searches. A systematic approach to study non-perturbative
emissions is required.

The PDFs and QCD radiation are closely associated. The DGLAP equations
describe the evolution of PDFs, which have been studied extensively in lepton-
nucleon inelastic-scattering experiments [9]. The DGLAP equations describe the
change in the quark density function of incoming quarks due to QCD processes:

$\frac{dq(x,Q^{2})}{d\ln{Q^{2}}}=\int_{x}^{1}\frac{dy}{y}\alpha_{s}(Q^{2})P_{q\rightarrow
qg}\left(\frac{x}{y},Q^{2}\right)q(y,Q^{2}).$ (1)

Here, $\alpha_{s}$ is the strong coupling constant which is a function of the
energy scale, $Q^{2}$. The term $q(y,Q^{2})$ is the quark density function
with momentum fraction $y~{}(>x)$ in the proton, and $P_{q\rightarrow qg}$ is
the QCD splitting function that gives the probability for the incoming quark
to split into a quark and a gluon. Since all of these QCD processes are
described by the DGLAP equations which have a logarithmic $Q^{2}$ dependence,
this study investigates the effects of QCD ISR as a function of $Q^{2}$.

The Drell-Yan (DY) production of lepton pairs $(p\bar{p}\to{Z/\gamma^{*}}\to
ee,{\mu\mu})$ is ideal to study QCD ISR. At the Born level, DY lepton pairs
are produced with zero transverse momentum. The emission of one or more gluons
from the initial-state quarks gives rise to a transverse momentum for these
quarks which then creates a non-zero transverse momentum for the DY lepton
pair. Thus, a transverse momomentum of the DY lepton pair is a good observable
to study the effect of QCD ISR. The final state of the DY lepton pair is free
from final-state QCD radiation. This simplifies the interpretation of the
measurements. In addition, the parton-parton energy scale $Q^{2}$ is
characterized by the squared dilepton mass $m_{{\ell\ell}}^{2}$.

Using Pythia8 [10] simulations, it is found that the truncated mean of
${p_{T}}$ distributions ${\langle p_{T}\rangle}$ for the DY process and other
DY-type process (such as $W$ boson or top-quark pair production) can be
described with a function linear in the logarithm of the energy scale of the
hard process with universal slope, as a consequence of the DGLAP evolution.
This universality is illustrated in Fig. 1, which shows the prediction for
${\langle p_{T}\rangle}$ of different processes, exhibiting a common
dependence on the energy scale $Q^{2}$. Since the recoil of the hard process
system due to ISR is the main factor of ${\langle p_{T}\rangle}$, it can be
used as a powerful observable to probe the effect of ISR.

Figure 1: Predicted ${\langle p_{T}\rangle}$ of the hard process system
(${Z/\gamma^{*}}$, $W$ or $t\bar{t}$) as a function of the energy scale
$Q^{2}$. Here, ${\langle p_{T}\rangle}$ is the truncated mean of the ${p_{T}}$
distribution with ${p_{T}}<100~{}{\rm{GeV}/\it{c}}$ and $Q^{2}$ is set as the
squared mass of ${Z/\gamma^{*}}$, $W$ or $t\bar{t}$, respectively. The values
shown are obtained from Pythia8 simulations of inclusive hadroproduction of
$Z/\gamma^{*}$, $W$ bosons, and top-antitop quark pairs.

This paper presents a novel approach to characterize the effect of ISR, which
can be observed in the average $p_{T}$ of DY lepton pairs as a function of the
energy scale $Q^{2}$. The measurements of the average $p_{T}$ at various
energy scales are performed using proton-antiproton ($p\bar{p}$) collision
data at center-of-mass energy $\sqrt{s}=$ 1.96 TeV produced by the Tevatron
collider and collected with the CDF II detector. The measured values are
corrected for QED final-state radiation (FSR) effects and the experimental
effects such as detector acceptance and resolution. Using such measurements a
relationship between the $p_{T}$ and mass-scale observables in the DY process
can be established. This may improve modeling of ISR phenomenology as well as
constrain its impact on the measurement of other processes in hadron
colliders.

##  II The Experimental Apparatus

The CDF II detector is a solenoidal magnetic spectrometer surrounded by
calorimeters and muon detectors, which operated at the Tevatron proton-
antiproton collider from 2001 until 2011. CDF II uses a cylindrical coordinate
system with the positive $z$-axis along the proton beam direction. For
particle trajectories, the polar angle $\theta$ is relative to the proton
direction and the azimuthal angle $\phi$ is oriented about the beamline axis
with $\pi/2$ being vertically upwards. Detector coordinates are specified as
($\eta,\phi$), where $\eta$ is the pseudorapidity defined as
$-\ln\tan(\theta/2)$. The detector is described in detail in Ref. [11].

The beam pipe is surrounded by a 2 m long silicon vertex-tracker covering a
pseudorapidity range of $|\eta|<2$ [12]. The central charged-particle tracking
detector, which is a 3.1 m long open-cell drift chamber, extends radially from
0.4 to 1.4 m covering the range $|\eta|<1.0$ [13]. Both trackers are
positioned in a 1.4 T axial magnetic field produced by a superconducting
solenoid surrounding the outer radius of the drift chamber. Outside the
solenoid is a central barrel calorimeter in the region $|\eta|<1.1$ [14, 15].
The forward end-cap regions are covered by plug calorimeters in the regions
$1.1<|\eta|<3.5$ [16]. Muon detectors are the outermost charged-particle
trackers and cover the region $|\eta|<1.5$ [17].

The data were collected using a three-level electronics system (trigger). The
first level, relying on special-purpose processors, and the second level,
using a mixture of dedicated processors and fast software algorithms, reduce
the event accept-rate to a level manageable by the data acquisition system.
The accepted events are processed online at the third-level trigger [18] with
fast reconstruction algorithms [19], and are recorded for offline analysis.

##  III Event Selection

The DY candidate muon-pairs were accepted online by a single-muon trigger [11]
with track ${p_{T}}$ threshold of 18 GeV/$c$. Electron candidate [11] pairs
were accepted online by single- and double-electron triggers [11, 20]. The
single-electron trigger requires at least one electron candidate with
transverse energy ${E_{T}}$ greater than 18 GeV and an associated track with
$p_{T}$ larger than 9 ${\rm{GeV}/\it{c}}$. For the double-electron trigger,
events are accepted when containing at least two electron candidates without
requiring an associated track.

Events collected are further required to pass the following offline-selection
criteria. Muon candidates are required to have matching track elements in the
muon chambers (except when the track extrapolates outward to an uninstrumented
region (gap) of the muon detector), and an energy deposition in the
calorimeters consistent with that for a minimum-ionizing particle [11]. Track-
quality selections are also imposed on the candidates. The selection of muon
pairs requires two oppositely-charged muon candidates with $|\eta|<$ 1.5. The
muon candidate with leading (sub-leading) $p_{T}$ is required to be larger
than 20 (12) ${\rm{GeV}/\it{c}}$.

Electron candidates are either reconstructed in the central electromagnetic
calorimeter or in the forward region covered by the plug electromagnetic
calorimeter [11]. Two levels of identification criteria are used for central-
electron candidates. High-quality criteria select ‘tight’ central electron
(TCE) candidates by requiring a matching good-quality track in the tracking
chamber and a shower profile consistent with that of an electron in the
electromagnetic calorimeter. Less stringent criteria select ’loose’ central
electron (LCE) candidates by relaxing some track- and shower-quality
requirements. Plug-electron identification uses plug electromagnetic
calorimeter information and requires an associated track reconstructed in the
silicon tracker.

Electron pairs are classified into three topologies depending on where each
electron candidate is reconstructed, central-central (CC, 40% of selected
candidates), central-plug (CP, 46%), and plug-plug (PP, 14%). For CC-topology
pairs, at least one electron candidate should pass TCE identification. The two
electron candidates are required to be oppositely charged, and the candidate
with leading (sub-leading) ${E_{T}}$ is required to have ${E_{T}}>$ 25 (15)
GeV. In the CP-topology, the central-electron candidate is required to pass
TCE criteria. Both electron candidates are required to have ${E_{T}}>$ 20 GeV.
The plug-electron pair candidates (PP-topology) are required to pass the plug-
electron identification criteria and to have ${E_{T}}>$ 25 GeV. In addition,
PP-topology pairs are requested to be contained in the same side plug detector
to reduce the QCD background, because the QCD multijet events tend to have
larger $\eta$ difference between the two leptons than DY events. The plug-
electron candidates have a poor charge identification because electron tracks
in the forward region are constructed only using silicon detector information
due to the small coverage of the drift chamber. Thus, the opposite-charge
requirement is not applied to CP- and PP-topology pairs. In order to reduce
misreconstructed events and contributions from background processes, the
transverse energy imbalance (${\not\\!\\!E_{T}}$) [21] associated to the
selected dielectron events is required to be lower than 40 GeV.

Dielectron events produced at the $Z$-mass peak may be reconstructed at much
lower masses if the electron loses a significant portion of its energy by
radiating photons. It is difficult to simulate photons from the QED FSR
process at small dielectron masses (${m_{ee}}$), where the effect is
comparatively more important due to this migration. To suppress the migration
effects, the following additional selection criteria are applied to the events
with dielectron invariant mass ${m_{ee}}<80~{}{{\rm GeV}/c^{2}}$ based on a
study using a DY simulated sample:

$\begin{array}[]{l}\begin{array}[]{l}\text{Reject\ if\
}|\Delta\phi(e_{1},e_{2})-\pi|<0.25\rm{\ and}\\\
\Big{\\{}\begin{array}[]{l}\Delta{p_{T}}(e_{1},e_{2})>15\
\text{\mbox{GeV/$\it{c}$} ,\ when}\ {\not\\!\\!E_{T}}<15\
\text{GeV}\\\\[4.30554pt] \Delta{p_{T}}(e_{1},e_{2})>10\
\text{\mbox{GeV/$\it{c}$} ,\ when}\ {\not\\!\\!E_{T}}>15\ \text{GeV}.\\\
\end{array}\end{array}\end{array}$

Here, $e_{1}$ and $e_{2}$ are the leading and the sub-leading electrons in
$p_{T}$ , $\Delta\phi(e_{1},e_{2})$ is the azimuthal opening angle of electron
pairs, and $\Delta{p_{T}}(e_{1},e_{2})$ is the scalar $p_{T}$ difference of
the two electrons.

Differences in acceptance and efficiency between simulation and data are
corrected by applying scale factors to the event yields reconstructed in
simulation. The trigger and identification scale factors for electrons are
obtained using unbiased electron samples in data as functions of
pseudorapidity, ${E_{T}}$, number of extra vertices in the event, and the time
when the events were collected. The scale factors for the muons depend on the
detector topology of the muon pair and data taking time. For the selected
electron- and muon-pair events of the simulation, the number of primary
vertices and the distribution of the vertices along the beamline are weighted
to match their corresponding distributions in data.

As this analysis focuses on QCD ISR mostly from non-perturbative QCD
emissions, all candidates are required to have the dilepton system transverse
momentum ${p_{T}^{\ell\ell}}<100~{}{\rm{GeV}/\it{c}}$. This selection also has
the benefit of removing events with poorly reconstructed muons, which tend to
have large measured ${p_{T}^{\ell\ell}}$ values.

##  IV Drell-Yan signal events and backgrounds

The selected dimuon events are dominated by the ${Z/\gamma^{*}}\to\mu\mu$
signal process, and there are also contributions from
${Z/\gamma^{*}}\to\tau\tau$, diboson (WW, WZ, ZZ), $t\bar{t}$, $W+$jets, and
QCD multijet processes, which are considered as backgrounds. They are all
estimated using simulation with the exception of the QCD multijet process. The
simulated samples are generated using Pythia6 [22] with tune AW [23] and
processed through the Geant3-based [24] CDF II detector simulation. The total
cross sections corresponding to the size of simulated samples are normalized
using NLO QCD calculations respectively [20, 25, 26]. Following the procedure
described in Ref. [27], the multijet background for dimuon events is
determined from the data using events with same-sign muon pairs assumed to
have same kinematics with opposite-sign events. Fig. 2 shows the distributions
of the dimuon mass, ${m_{\mu\mu}}$, for the SM processes considered and for
the experimental data. The dimuon event yields for the data and the expected
SM contributions are shown in Table 1 for various dimuon-mass ranges. Given
that only statistical uncertainties are considered, the predictions show good
agreement with the data.

Figure 2: Observed dimuon mass distribution in data (circles) compared with the distributions from expected SM contributions (stacked). The normalized residuals of the data and the SM prediction are shown in the lower panel. Only statistical uncertainties are considered in both panels. Table 1: The number of observed dimuon events and the number of estimated events with statistical uncertainties in the full CDF II sample, corresponding to 9.4 $\mathrm{fb^{-1}}$ of integrated luminosity, in five dimuon-mass ranges. The fractions for the individual SM processes are listed below the dashed line. $m_{\mu\mu}$ (${{\rm GeV}/c^{2}}$) | $[40,60]$ | $[60,80]$ | $[80,100]$ | $[100,200]$ | $[200,350]$
---|---|---|---|---|---
Data yield | $16754$ | $18471$ | $244729$ | $13089$ | $562$
Estimated yield | $15975\pm 36$ | $17786\pm 30$ | $244248\pm 100$ | $13184\pm 24$ | $580\pm 5$
${Z/\gamma^{*}}\to{\mu\mu}$ | 91.45% | 97.42% | 99.86% | 98.99% | 97.78%
QCD multijet | 2.82% | 0.54% | 0.01% | 0.09% | 0.04%
${Z/\gamma^{*}}\to\tau\tau$ | 4.85% | 1.40% | 0.01% | 0.06% | 0.02%
Diboson | 0.42% | 0.40% | 0.12% | 0.52% | 1.32%
$W$+jets | 0.29% | 0.07% | 0.00% | 0.04% | 0.00%
$t\bar{t}$ | 0.17% | 0.16% | 0.01% | 0.31% | 0.84%

For the electron channel, the ${Z/\gamma^{*}}\to ee$ signal process is the
main contribution, and ${Z/\gamma^{*}}\to\tau\tau$, diboson (WW, WZ, ZZ),
$t\bar{t}$, $W+$jets, $W\gamma$, and QCD multijet processes are considered as
backgrounds. As in the case of the dimuon final state, all processes are
modeled using simulation except for QCD multijet production, which is
estimated from data. The dielectron mass shape of QCD multijet events is
obtained from data selected through inverse electron isolation requirements
and normalized using a fit to the experimental dielectron mass distribution
following Ref. [20]. The sum of the expected SM processes agrees with the data
as shown in Fig. 3 and Table 2.

Figure 3: Observed dielectron mass distribution in data (circles) compared with the distributions from expected SM contributions (stacked). The normalized residuals of the data and the SM prediction are shown in the lower panel. Only statistical uncertainties are considered in both panels. Table 2: The number of observed dielectron events and the number of estimated events with statistical uncertainties in the full CDF II sample, corresponding to 9.4 $\mathrm{fb^{-1}}$ of integrated luminosity, in five dielectron-mass ranges. The fractions for the individual SM processes are listed below the dashed line. $m_{ee}$ (${{\rm GeV}/c^{2}}$) | $[40,60]$ | $[60,80]$ | $[80,100]$ | $[100,200]$ | $[200,350]$
---|---|---|---|---|---
Data yield | $11590$ | $28856$ | $490211$ | $27956$ | $1357$
Estimated yield | $11416\pm 53$ | $28374\pm 54$ | $493391\pm 158$ | $27481\pm 51$ | $1307\pm 15$
${Z/\gamma^{*}}\to ee$ | 85.88% | 93.78% | 99.70% | 94.67% | 85.12%
QCD multijet | 7.58% | 3.45% | 0.18% | 3.96% | 10.98%
${Z/\gamma^{*}}\to\tau\tau$ | 4.70% | 1.95% | 0.01% | 0.06% | 0.12%
Diboson | 0.33% | 0.22% | 0.08% | 0.35% | 1.15%
$W$+jets | 1.03% | 0.43% | 0.02% | 0.62% | 1.48%
$W\gamma$ | 0.43% | 0.13% | 0.01% | 0.25% | 0.87%
$t\bar{t}$ | 0.07% | 0.03% | 0.00% | 0.09% | 0.28%

##  V ISR Measurement in Drell-Yan Events

The effect of the QCD ISR is probed by measuring the truncated mean of
$Z/\gamma^{*}$ $p_{T}$ distribution in bins of the lepton-pair mass. Several
corrections relevant for this measurement are described in this section.

First, the lepton energy and momentum are calibrated to correct for
instrumental effects. For the measurement using muon pairs, multiplicative and
additive corrections are applied to the muon-track curvature as functions of
the track pseudorapidity and azimuthal angle to correct inaccuracies of the
magnetic field description and misalignment [27, 28]. The curvature resolution
of the simulation is adjusted to match the data. For electron calibrations,
the method used is similar, and multiplicative and additive corrections are
applied to the electron energy as functions of data taking time, individual
calorimeter tower, and the number of primary vertices [20]. The calorimeter
resolution in simulation is also adjusted to agree with the data.

The simulated ${p_{T}^{\ell\ell}}$ distribution is sensitive to the chosen
model for the QCD ISR. The parton-shower algorithm in Pythia6 uses a soft-
collinear approximation, which is fast and efficient but is restricted in
precision to the leading logarithmic order in the approximation used. This
approach sums all emissions by evolving from large to small $Q^{2}$ by
reformulating the DGLAP equations. Uncertainties in this evolution and missing
higher-order effects may introduce a mismodeling of the ${p_{T}^{\ell\ell}}$
distribution. Mistuning of the intrinsic transverse momentum of the incoming
partons may also contribute to an inaccuracy. Consequently, the simulated
${p_{T}^{\ell\ell}}$ distribution is adjusted to agree with the data by
reweighting the $Z/\gamma^{*}$ boson $p_{T}$ at the generator level, where the
correction is assumed to be independent of the lepton flavor. This correction
is iteratively extracted from the reconstructed ${p_{T}^{\ell\ell}}$
distributions of both dielectron and dimuon events within the $Z$-peak mass
region of 66–116 ${{\rm GeV}/c^{2}}$. The correction is a function of the
$p_{T}$ and the rapidity of the boson. The $p_{T}$ dependence of the weight is
parametrized using a continuous piecewise polynomial function of
$\ln({p_{T}})$ and the rapidity dependence is parametrized using a linear
function.

Fig. 4 and Fig. 5 show the reconstructed ${p_{T}^{\ell\ell}}$ distribution of
the background-subtracted data and the simulated DY events after applying the
corrections described above. Good agreement is observed between simulation and
data for both $ee$ and ${\mu\mu}$ final states.

Figure 4: Distributions of the reconstructed dimuon ${p_{T}}$ in data (black
circle) compared with distributions from the DY simulation after applying the
${Z/\gamma^{*}}$ boson ${p_{T}}$ corrections in each dimuon mass bin: (a)
$[40~{}{{\rm GeV}/c^{2}},~{}60~{}{{\rm GeV}/c^{2}}]$, (b) $[60~{}{{\rm
GeV}/c^{2}},~{}80~{}{{\rm GeV}/c^{2}}]$, (c) $[80~{}{{\rm
GeV}/c^{2}},~{}100~{}{{\rm GeV}/c^{2}}]$, (d) $[100~{}{{\rm
GeV}/c^{2}},~{}200~{}{{\rm GeV}/c^{2}}]$, (e) $[200~{}{{\rm
GeV}/c^{2}},~{}350~{}{{\rm GeV}/c^{2}}]$. Other backgrounds are subtracted
from the data and the normalized residuals of the data and the DY simulation
are shown in the lower panels. Statistical uncertainties (black bar) and
systematic uncertainties (red shaded area) are shown.

Figure 5: Distributions of the reconstructed dielectron ${p_{T}}$ in data
(black circle) compared with distributions from the DY simulation after
applying the ${Z/\gamma^{*}}$ boson ${p_{T}}$ corrections in each dielectron
mass bin: (a) $[40~{}{{\rm GeV}/c^{2}},~{}60~{}{{\rm GeV}/c^{2}}]$, (b)
$[60~{}{{\rm GeV}/c^{2}},~{}80~{}{{\rm GeV}/c^{2}}]$, (c) $[80~{}{{\rm
GeV}/c^{2}},~{}100~{}{{\rm GeV}/c^{2}}]$, (d) $[100~{}{{\rm
GeV}/c^{2}},~{}200~{}{{\rm GeV}/c^{2}}]$, (e) $[200~{}{{\rm
GeV}/c^{2}},~{}350~{}{{\rm GeV}/c^{2}}]$. Other backgrounds are subtracted
from the data and the normalized residuals of the data and the DY simulation
are shown in the lower panels. Statistical uncertainties (black bar) and
systematic uncertainties (red shaded area) are shown.

The mean values of the $Z/\gamma^{*}$ transverse momentum $\langle
p_{T}^{\mathrm{DY}}\rangle$ in DY events are obtained from the average values
of the reconstructed $p_{T}^{\ell\ell}$ distribution $\langle
p_{T}^{\ell\ell}\rangle$ by multiplying corrections for acceptance, detector
and QED FSR effects. The mean values of the $Z/\gamma^{*}$ mass ${\langle
m_{\mathrm{DY}}\rangle}$ are also obtained from the average values of the
reconstructed lepton-pair mass ${\langle{m_{{\ell\ell}}}\rangle}$ by the same
procedure. Combined corrections for the average $p_{T}$ and mass of the lepton
pairs within a mass bin, denoted by $\mathcal{R}_{{p_{T}}}$ and
$\mathcal{R}_{\rm m}$ respectively, are derived from the simulated DY sample
and applied as shown below,

$\displaystyle{\langle p_{T}^{\mathrm{DY}}\rangle}_{\mathrm{data}}$
$\displaystyle=\mathcal{R}_{{p_{T}}}\times{\langle
p_{T}^{\ell\ell}\rangle}_{\mathrm{data}}$ (2) $\displaystyle\text{where
}\mathcal{R}_{{p_{T}}}$ $\displaystyle\equiv\frac{{\langle
p_{T}^{\mathrm{DY}}\rangle}^{\mathrm{gen}}_{\mathrm{MC}}}{{\langle
p_{T}^{\ell\ell}\rangle}^{\mathrm{det}}_{\mathrm{MC}}},$
$\displaystyle{\langle{m_{\mathrm{DY}}}\rangle}_{\mathrm{data}}$
$\displaystyle=\mathcal{R}_{\rm
m}\times{\langle{m_{{\ell\ell}}}\rangle}_{\mathrm{data}}$ (3)
$\displaystyle\text{where }\mathcal{R}_{\rm m}$
$\displaystyle\equiv\frac{{\langle{m_{\mathrm{DY}}}\rangle}^{\mathrm{gen}}_{\mathrm{MC}}}{{\langle{m_{{\ell\ell}}}\rangle}^{\mathrm{det}}_{\mathrm{MC}}}.$

Here, ${\langle p_{T}^{\mathrm{DY}}\rangle}^{\mathrm{gen}}_{\mathrm{MC}}$ and
$\langle{m_{\mathrm{DY}}}\rangle^{\mathrm{gen}}_{\mathrm{MC}}$ are generator-
level averages over the full phase space within a mass bin, and ${\langle
p_{T}^{\ell\ell}\rangle}^{\mathrm{det}}_{\mathrm{MC}}$ and
$\langle{m_{{\ell\ell}}}\rangle^{\mathrm{det}}_{\mathrm{MC}}$ are detector-
level averages corresponding to the data. The corrections for $p_{T}$
($\mathcal{R}_{{p_{T}}}$) range from 0.75 to 1.00 and the corrections for $m$
($\mathcal{R}_{\rm m}$) range from 0.82 to 1.01.

##  VI Systematic Uncertainties

The QCD ISR model, QED FSR model, energy and momentum corrections on leptons,
and background normalizations are sources of systematic uncertainty of the
measurements of ${\langle p_{T}^{\mathrm{DY}}\rangle}$ and ${\langle
m_{\mathrm{DY}}\rangle}$. The uncertainties of ${\langle
p_{T}^{\mathrm{DY}}\rangle}$ for the dimuon and dielectron final states are
listed in Tables 3 and 4, respectively. The QCD ISR model and QED FSR model
uncertainties dominate.

The QCD ISR uncertainty is defined to be the uncertainty of the underlying
${Z/\gamma^{*}}$-boson $p_{T}$ distribution used in the DY simulation. The
simulated $Z/\gamma^{*}$ boson $p_{T}^{\ell\ell}$ distribution is improved by
reweighting the $p_{T}$ distribution so as to agree with the data. Two sources
of uncertainty of this correction are considered: the correction derived from
events in the $Z$-mass region to mass values away from the $Z$ peak, and the
statistical uncertainty to the correction. The QCD ISR uncertainty is
estimated using a set of simulated experiments in which the input values are
varied within uncertainties from both sources.

The reconstructed ${Z/\gamma^{*}}$ mass and $p_{T}$ can be affected by the
presence of QED FSR which is not fully contained in the reconstructed event
products. The simulation accounts for this in the correction factors
$\mathcal{R}_{{p_{T}}}$ and $\mathcal{R}_{\rm m}$. The default model of QED
FSR in Pythia6 is augmented with a QED shower algorithm which could be
inaccurate for hard QED emissions. The Photos QED generator [29] calculates
single-photon radiation in the leading order of the electromagnetic
interaction and simulates multiphoton radiation by iterating the single-photon
calculation. To estimate the QED FSR uncertainty to the correction factors,
the generator-level results for ${\langle p_{T}^{\mathrm{DY}}\rangle}$ and
${\langle m_{\mathrm{DY}}\rangle}$ before and after QED FSR are evaluated for
Pythia6 and Photos. The difference is taken as the QED FSR uncertainty.

The systematic uncertainty due to the electron energy and muon momentum scales
is estimated using simulated samples by varying the scales within their
uncertainties. The systematic uncertainty due to simulation inaccuracies in
the energy and momentum resolution is evaluated by varying the simulation
parameters that control the resolution smearing.

The uncertainties from the simulation-based description of the background
processes are estimated by changing each cross section by its uncertainty,
where the factorization, renormalization, and PDF uncertainties are
considered. The 6% uncertainty on the determination of the integrated
luminosity [20] is included. The background normalizations are treated as 100%
correlated.

Using averages of ${m_{\mathrm{DY}}}$ over large bins may lead to biased
results when representing ${\langle p_{T}^{\mathrm{DY}}\rangle}$ as a function
of ${m_{\mathrm{DY}}}$ [30]. The additional systematic uncertainties
accounting for this binning effect are considered for $\langle
m_{\mathrm{DY}}\rangle$ measurement by taking the difference between
$\ln{{\langle m_{\mathrm{DY}}\rangle}^{2}}$ and
$\langle\ln{m_{\mathrm{DY}}^{2}}\rangle$. This is the dominant systematic
uncertainty for the ${\langle m_{\mathrm{DY}}\rangle}$ measurement, and ranges
from 0.04% to 1.13%.

Table 3: Fractional statistical and systematic uncertainties of $\langle p_{T}^{\mathrm{DY}}\rangle$ (in %) for each dimuon mass bin. Individual sources of systematic uncertainties are listed below the dashed line. Mass bin (${{\rm GeV}/c^{2}}$) | $[40,60]$ | $[60,80]$ | $[80,100]$ | $[100,200]$ | $[200,350]$
---|---|---|---|---|---
Statistical uncertainty (%) | 0.96 | 0.73 | 0.22 | 0.95 | 3.79
Systematic uncertainty (%) | 1.29 | 1.33 | 0.26 | 0.90 | 2.76
ISR model (%) | 0.90 | 0.93 | 0.24 | 0.50 | 2.28
QED FSR model (%) | 0.87 | 0.93 | 0.03 | 0.18 | 0.41
Momentum scale (%) | 0.12 | 0.13 | 0.04 | 0.20 | 0.86
Momentum resolution (%) | 0.07 | 0.06 | 0.08 | 0.68 | 1.20
Background normalization (%) | 0.28 | 0.10 | 0.03 | 0.16 | 0.25
Table 4: Fractional statistical and systematic uncertainties of $\langle p_{T}^{\mathrm{DY}}\rangle$ (in %) for each dielectron mass bin. Individual sources of systematic uncertainties are listed below the dashed line. Mass bin (${{\rm GeV}/c^{2}}$) | $[40,60]$ | $[60,80]$ | $[80,100]$ | $[100,200]$ | $[200,350]$
---|---|---|---|---|---
Statistical uncertainty (%) | 1.38 | 0.70 | 0.16 | 0.72 | 3.44
Systematic uncertainty (%) | 2.03 | 0.89 | 0.12 | 0.69 | 2.11
ISR model (%) | 1.37 | 0.47 | 0.06 | 0.33 | 1.68
QED FSR model (%) | 1.39 | 0.72 | 0.05 | 0.22 | 0.67
Energy scale (%) | 0.13 | 0.08 | 0.02 | 0.07 | 0.19
Energy resolution (%) | 0.02 | 0.02 | 0.08 | 0.10 | 0.15
Background normalization (%) | 0.57 | 0.21 | 0.03 | 0.56 | 1.06

##  VII Results

The measurements of ${\langle p_{T}^{\mathrm{DY}}\rangle}$ and
${\langle{m_{\mathrm{DY}}}\rangle}$ in DY events are obtained for dimuon and
dielectron final states. The dimuon and dielectron results are in good
agreement as shown in Table 5 and Table 6. The results are combined using the
best linear unbiased estimation [31] and are given in Table 7. Systematic
uncertainties are combined accounting for all the correlations between final
states and are listed in Table 8. Fig. 6 shows the dependence of ${\langle
p_{T}^{\mathrm{DY}}\rangle}$ as a function of $\ln{m_{\mathrm{DY}}^{2}}$,
which is modeled by the linear function

${\langle p_{T}^{\mathrm{DY}}\rangle}=(-7.56\pm 0.83)+(2.15\mp
0.09)\ln{m_{\mathrm{DY}}^{2}}~{}[{\rm{GeV}/\it{c}}],$ (4)

where $m_{\mathrm{DY}}$ is the value of the $Z/\gamma^{*}$ mass measured in
units of ${{\rm GeV}/c^{2}}$. The average symbol for $m_{\mathrm{DY}}$ is
omitted as the additional systematic uncertainty for the binning effect is
included. The two fitted parameters are found to be strongly anti-correlated
(-99.97%)111One can reduce the correlation between the two parameters for
easier interpretation by using a modified fitting function ${\langle
p_{T}^{\mathrm{DY}}\rangle}=(11.82\pm 0.02)+(2.15\pm
0.09)\ln{{m_{\mathrm{DY}}^{2}}\over{m^{2}_{Z\mathrm{,pole}}}}~{}[{\rm{GeV}/\it{c}}]$,
where $m_{Z\mathrm{,pole}}$ is 91.19 ${{\rm GeV}/c^{2}}$. In this case, the
two parameters are positively correlated by approximately 12%..

Table 5: Average values and their uncertainties of the dimuon mass and ${p_{T}}$ for ${\mu\mu}$ events. Mass bin (${{\rm GeV}/c^{2}}$) |  |  ${\langle m_{\mathrm{DY}}\rangle}{\pm}{\rm stat}{\pm}{\rm syst}$ (${{\rm GeV}/c^{2}}$) |  |  ${\langle p_{T}^{\mathrm{DY}}\rangle}{\pm}{\rm stat}{\pm}{\rm syst}$ (${{\rm GeV}/c^{2}}$)
---|---|---|---|---
$[40,60]$ |  | $47.72\pm 0.05\pm 0.31$ |  | $9.12\pm 0.09\pm 0.12$
$[60,80]$ |  | $70.66\pm 0.04\pm 0.27$ |  | $10.81\pm 0.08\pm 0.14$
$[80,100]$ |  | $90.99\pm 0.01\pm 0.08$ |  | $11.84\pm 0.03\pm 0.03$
$[100,200]$ |  | $115.29\pm 0.18\pm 1.30$ |  | $13.17\pm 0.12\pm 0.12$
$[200,350]$ |  | $243.33\pm 1.63\pm 2.52$ |  | $16.18\pm 0.61\pm 0.45$
Table 6: Average values and their uncertainties of the dielectron mass and ${p_{T}}$ for $ee$ events. Mass bin (${{\rm GeV}/c^{2}}$) |  |  ${\langle m_{\mathrm{DY}}\rangle}{\pm}{\rm stat}{\pm}{\rm syst}$ (${{\rm GeV}/c^{2}}$) |  |  ${\langle p_{T}^{\mathrm{DY}}\rangle}{\pm}{\rm stat}{\pm}{\rm syst}$ (${{\rm GeV}/c^{2}}$)
---|---|---|---|---
$[40,60]$ |  | $47.83\pm 0.05\pm 0.31$ |  | $9.10\pm 0.13\pm 0.18$
$[60,80]$ |  | $70.76\pm 0.04\pm 0.26$ |  | $10.84\pm 0.08\pm 0.10$
$[80,100]$ |  | $90.98\pm 0.01\pm 0.08$ |  | $11.79\pm 0.02\pm 0.01$
$[100,200]$ |  | $115.11\pm 0.13\pm 1.31$ |  | $12.93\pm 0.09\pm 0.09$
$[200,350]$ |  | $245.46\pm 1.29\pm 2.61$ |  | $16.41\pm 0.56\pm 0.35$
Table 7: Average values and their uncertainties of the lepton-pair mass and ${p_{T}}$, combining $ee$ and ${\mu\mu}$ events. Mass bin (${{\rm GeV}/c^{2}}$) |  |  ${\langle m_{\mathrm{DY}}\rangle}{\pm}{\rm stat}{\pm}{\rm syst}$ (${{\rm GeV}/c^{2}}$) |  |  ${\langle p_{T}^{\mathrm{DY}}\rangle}{\pm}{\rm stat}{\pm}{\rm syst}$ (${{\rm GeV}/c^{2}}$)
---|---|---|---|---
$[40,60]$ |  | $47.77\pm 0.04\pm 0.31$ |  | $9.12\pm 0.09\pm 0.12$
$[60,80]$ |  | $70.75\pm 0.03\pm 0.26$ |  | $10.84\pm 0.07\pm 0.10$
$[80,100]$ |  | $90.98\pm 0.00\pm 0.08$ |  | $11.80\pm 0.02\pm 0.02$
$[100,200]$ |  | $115.19\pm 0.11\pm 1.30$ |  | $13.01\pm 0.07\pm 0.09$
$[200,350]$ |  | $244.49\pm 1.02\pm 2.56$ |  | $16.32\pm 0.42\pm 0.36$
Table 8: Statistical and systematic uncertainties of $\langle p_{T}^{\mathrm{DY}}\rangle$ in the combined dielectron and dimuon final states. Fractional uncertainties are shown for the various dilepton mass bins and each systematic source. Mass bin (${{\rm GeV}/c^{2}}$) | [40,60] | [60,80] | [80,100] | [100,200] | [200,350]
---|---|---|---|---|---
Statistical uncertainty (%) | 0.96 | 0.62 | 0.14 | 0.57 | 2.56
Systematic uncertainty (%) | 1.29 | 0.93 | 0.13 | 0.66 | 2.23
ISR model (%) | 0.90 | 0.52 | 0.09 | 0.39 | 1.93
QED FSR model (%) | 0.87 | 0.74 | 0.05 | 0.20 | 0.56
Muon momentum scale (%) | 0.12 | 0.01 | 0.01 | 0.07 | 0.35
Electron energy scale (%) | 0.00 | 0.07 | 0.01 | 0.05 | 0.11
Muon momentum resolution (%) | 0.07 | 0.01 | 0.02 | 0.22 | 0.49
Electron energy resolution (%) | 0.00 | 0.02 | 0.07 | 0.07 | 0.09
Background normalization (%) | 0.28 | 0.20 | 0.03 | 0.43 | 0.73
Figure 6: Average transverse momentum of $Z/\gamma^{*}$
(${p_{T}^{\mathrm{DY}}}$) as a function of $\ln{m_{\mathrm{DY}}^{2}}$ fitted
with a linear function. Statistical and systematic uncertainties are included
in the results of the fit.

##  VIII Conclusions

This analysis presents a novel approach to characterize the effect of QCD ISR
and a measurement of the ISR activity in DY events produced in proton-
antiproton collisions at $\sqrt{s}~{}=~{}1.96$ TeV, corresponding to an
integrated luminosity of 9.4 fb-1. The measurement of the average lepton-pair
$p_{T}$ distribution is performed as a function of the dilepton invariant mass
to quantify the effect of ISR activity. The average value of the lepton-pair
${p_{T}}$ is found to have a linear dependence on $\ln{m_{\mathrm{DY}}^{2}}$.
The dependence is described by the function, ${\langle
p_{T}^{\mathrm{DY}}\rangle}=A+B\ln{m_{\mathrm{DY}}^{2}}$, where the parameters
A and B are obtained by a linear fit to be $-7.56\pm 0.83~{}{\rm{GeV}/\it{c}}$
and $2.15\mp 0.09~{}{\rm{GeV}/\it{c}}$, respectievly. The linear dependence is
an original finding of this work and may be exploited to improve the modeling
of ISR. Since there is no theoretical prediction of this measurement,
theorists may usefully make calculations of this measurement under various
models of ISR. In addition, by means of a linear extrapolation this finding
can be used to estimate the expected ISR activity at higher masses and is
relevant to searches for BSM particles.

###### Acknowledgements.

This document was prepared by the CDF collaboration using the resources of the
Fermi National Accelerator Laboratory (Fermilab), a U.S. Department of Energy,
Office of Science, HEP User Facility. Fermilab is managed by Fermi Research
Alliance, LLC (FRA), acting under Contract No. DE-AC02-07CH11359. We thank the
Fermilab staff and the technical staffs of the participating institutions for
their vital contributions. This work was supported by the U.S. Department of
Energy and National Science Foundation; the Italian Istituto Nazionale di
Fisica Nucleare; the Ministry of Education, Culture, Sports, Science and
Technology of Japan; the Natural Sciences and Engineering Research Council of
Canada; the National Science Council of the Republic of China; the Swiss
National Science Foundation; the A.P. Sloan Foundation; the Bundesministerium
für Bildung und Forschung, Germany; the National Research Foundation of Korea
and the Promising-Pioneering Researcher Program through Seoul National
University; the Science and Technology Facilities Council and the Royal
Society, United Kingdom; the Russian Foundation for Basic Research; the
Ministerio de Ciencia e Innovación, and Programa Consolider-Ingenio 2010,
Spain; the Slovak R&D Agency; the Academy of Finland; and the Australian
Research Council (ARC).

## References

  * [1] G. Aad et al. (ATLAS Collaboration), Phys. Lett. B 716 1 (2012).
  * [2] S. Chatrchyan et al. (CMS Collaboration), Phys. Lett. B 716 30 (2012).
  * [3] T. Aaltonen et al. (CDF Collaboration), Phys. Rev. D 91, 012002 (2015).
  * [4] Y.L. Dokshitzer, Sov. Phys. JETP, 46, 641 (1977).
  * [5] V.N. Gribov and L.N. Lipatov, Sov. J. Nucl. Phys. 15, 438 (1972).
  * [6] L.N. Lipatov, Sov. J. Nucl. Phys. 20, 93 (1975).
  * [7] G. Altarelli and G. Parisi, Nucl. Phys. B126, 298 (1977).
  * [8] T. Aaltonen et al. (CDF Collaboration), Phys. Rev. Lett. 107, 232002 (2011).
  * [9] H. Abramowicz et al. (H1 and ZEUS Collaborations), Eur. Phys. J. C 75, 580 (2015).
  * [10] T. Sjöstrand, S. Ask, J.R. Christiansen, R. Corke, N. Desai, P. Ilten, S. Mrenna, S. Prestel, C.O. Rasmussen, and P.Z. Skands, Comput. Phys. Commun. 191, 159 (2015).
  * [11] A. Abulencia et al. (CDF Collaboration), J. Phys. G 34, 2457 (2007).
  * [12] T. Aaltonen et al., Nucl. Instrum. Meth. A 729, 153 (2013).
  * [13] T. Affolder et al., Nucl. Instrum. Meth. A 526, 249 (2004).
  * [14] T. Affolder et al., Nucl. Instrum. Meth. A 267, 272 (1988).
  * [15] S. Bertolucci et al., Nucl. Instrum. Meth. A 267, 301 (1988).
  * [16] M. Albrow et al., Nucl. Instrum. Meth. A 480, 524 (2002).
  * [17] A. Artikov et al., Nucl. Instrum. Meth. A 538, 358 (2005).
  * [18] Y. S. Chung et al., IEEE Trans. Nucl. Sci. 52, 1212 (2005).
  * [19] G. Gomez-Ceballos et al., Nucl. Instrum. Meth. A 518, 522 (2004).
  * [20] T. Aaltonen et al. (CDF Collaboration), Phys. Rev. D 93, 112016 (2016).
  * [21] The calorimeters have a tower-geometry segmentation with towers pointing to the center of the detector. Transverse energy imbalance ${\not\\!\\!E_{T}}$ is the magnitude of $-\sum_{i}E_{T}^{i}\hat{n}_{i}$, where the sum is over calorimeter towers, $\hat{n}_{i}$ is the unit vector normal to beam direction and pointing to a given tower, and $E_{T}^{i}$ is the transverse energy measured in that tower.
  * [22] T. Sjöstrand, P. Eden, C. Friberg, L. Lönnblad, G. Miu, S. Mrenna, and E. Norrbin, Comput. Phys. Commun. 135, 238 (2001).
  * [23] M. Albrow et al. (Tev4LHC QCD Working Group), arXiv:hep-ph/0610012.
  * [24] R. Brun, R. Hagelberg, M. Hansroul, and J. C. Lassalle, CERN Reports No. CERN-DD-78-2-REV and No. CERN-DD-78-2.
  * [25] J. M. Campbell and R. K. Ellis, Phys. Rev. D 60, 113006 (1999).
  * [26] N. Kidonakis and R. Vogt, Eur. Phys. J. C 33, S466 (2004).
  * [27] T. Aaltonen et al. (CDF Collaboration), Phys. Rev. D 89, 072005 (2014).
  * [28] A. Bodek, A. van Dyne, J.Y. Han, W. Sakumoto, and A. Strelnikov, Eur. Phys. J. C 72, 2194 (2012).
  * [29] N. Davidson, T. Przedzinski, and Z. Was, Comput. Phys. Commun. 199, 86 (2016).
  * [30] G.D. Lafferty and T.R. Wyatt, Nucl. Instrum. Meth. A 355, 541 (1995).
  * [31] L. Lyons et al., Nucl. Instrum. Meth. A 270, 110 (1988).