BELLE2-CONF-PH-2020-003

Belle II Collaboration

# Measurement of the $B^{0}$ lifetime using fully reconstructed hadronic
decays in the 2019 Belle II dataset

F. Abudinén  INFN Sezione di Trieste, I-34127 Trieste, Italy  I. Adachi  High
Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The
Graduate University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan
R. Adak  Key Laboratory of Nuclear Physics and Ion-beam Application (MOE) and
Institute of Modern Physics, Fudan University, Shanghai 200443, China  K.
Adamczyk  H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342,
Poland  P. Ahlburg  University of Bonn, 53115 Bonn, Germany  J. K. Ahn  Korea
University, Seoul 02841, South Korea  H. Aihara  Department of Physics,
University of Tokyo, Tokyo 113-0033, Japan  N. Akopov  Alikhanyan National
Science Laboratory, Yerevan 0036, Armenia  A. Aloisio  Dipartimento di Scienze
Fisiche, Università di Napoli Federico II, I-80126 Napoli, Italy  INFN Sezione
di Napoli, I-80126 Napoli, Italy  F. Ameli  INFN Sezione di Roma, I-00185
Roma, Italy  L. Andricek  Semiconductor Laboratory of the Max Planck Society,
81739 München, Germany  N. Anh Ky  Institute of Physics, Vietnam Academy of
Science and Technology (VAST), Hanoi, Vietnam  D. M. Asner  Brookhaven
National Laboratory, Upton, New York 11973, U.S.A.  H. Atmacan  University of
Cincinnati, Cincinnati, Ohio 45221, U.S.A.  V. Aulchenko  Budker Institute of
Nuclear Physics SB RAS, Novosibirsk 630090, Russian Federation  Novosibirsk
State University, Novosibirsk 630090, Russian Federation  T. Aushev  Higher
School of Economics (HSE), Moscow 101000, Russian Federation  V. Aushev  Taras
Shevchenko National Univ. of Kiev, Kiev, Ukraine  T. Aziz  Tata Institute of
Fundamental Research, Mumbai 400005, India  V. Babu  Deutsches
Elektronen–Synchrotron, 22607 Hamburg, Germany  S. Bacher  H. Niewodniczanski
Institute of Nuclear Physics, Krakow 31-342, Poland  S. Baehr  Institut für
Experimentelle Teilchenphysik, Karlsruher Institut für Technologie, 76131
Karlsruhe, Germany  S. Bahinipati  Indian Institute of Technology Bhubaneswar,
Satya Nagar 751007, India  A. M. Bakich  School of Physics, University of
Sydney, New South Wales 2006, Australia  P. Bambade  Université Paris-Saclay,
CNRS/IN2P3, IJCLab, 91405 Orsay, France  Sw. Banerjee  University of
Louisville, Louisville, Kentucky 40292, U.S.A.  S. Bansal  Panjab University,
Chandigarh 160014, India  M. Barrett  High Energy Accelerator Research
Organization (KEK), Tsukuba 305-0801, Japan  W. Bartel  Deutsches
Elektronen–Synchrotron, 22607 Hamburg, Germany  G. Batignani  Dipartimento di
Fisica, Università di Pisa, I-56127 Pisa, Italy  INFN Sezione di Pisa, I-56127
Pisa, Italy  J. Baudot  Université de Strasbourg, CNRS, IPHC, UMR 7178, 67037
Strasbourg, France  A. Beaulieu  University of Victoria, Victoria, British
Columbia, V8W 3P6, Canada  J. Becker  Institut für Experimentelle
Teilchenphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
P. K. Behera  Indian Institute of Technology Madras, Chennai 600036, India  M.
Bender  Ludwig Maximilians University, 80539 Munich, Germany  J. V. Bennett
University of Mississippi, University, Mississippi 38677, U.S.A.  E. Bernieri
INFN Sezione di Roma Tre, I-00146 Roma, Italy  F. U. Bernlochner  University
of Bonn, 53115 Bonn, Germany  M. Bertemes  Institute of High Energy Physics,
Vienna 1050, Austria  M. Bessner  University of Hawaii, Honolulu, Hawaii
96822, U.S.A.  S. Bettarini  Dipartimento di Fisica, Università di Pisa,
I-56127 Pisa, Italy  INFN Sezione di Pisa, I-56127 Pisa, Italy  V. Bhardwaj
Indian Institute of Science Education and Research Mohali, SAS Nagar, 140306,
India  B. Bhuyan  Indian Institute of Technology Guwahati, Assam 781039, India
F. Bianchi  Dipartimento di Fisica, Università di Torino, I-10125 Torino,
Italy  INFN Sezione di Torino, I-10125 Torino, Italy  T. Bilka  Faculty of
Mathematics and Physics, Charles University, 121 16 Prague, Czech Republic  S.
Bilokin  Ludwig Maximilians University, 80539 Munich, Germany  D. Biswas
University of Louisville, Louisville, Kentucky 40292, U.S.A.  A. Bobrov
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090, Russian
Federation  Novosibirsk State University, Novosibirsk 630090, Russian
Federation  A. Bondar  Budker Institute of Nuclear Physics SB RAS, Novosibirsk
630090, Russian Federation  Novosibirsk State University, Novosibirsk 630090,
Russian Federation  G. Bonvicini  Wayne State University, Detroit, Michigan
48202, U.S.A.  A. Bozek  H. Niewodniczanski Institute of Nuclear Physics,
Krakow 31-342, Poland  M. Bračko  University of Maribor, 2000 Maribor,
Slovenia  J. Stefan Institute, 1000 Ljubljana, Slovenia  P. Branchini  INFN
Sezione di Roma Tre, I-00146 Roma, Italy  N. Braun  Institut für
Experimentelle Teilchenphysik, Karlsruher Institut für Technologie, 76131
Karlsruhe, Germany  R. A. Briere  Carnegie Mellon University, Pittsburgh,
Pennsylvania 15213, U.S.A.  T. E. Browder  University of Hawaii, Honolulu,
Hawaii 96822, U.S.A.  D. N. Brown  University of Louisville, Louisville,
Kentucky 40292, U.S.A.  A. Budano  INFN Sezione di Roma Tre, I-00146 Roma,
Italy  L. Burmistrov  Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405
Orsay, France  S. Bussino  Dipartimento di Matematica e Fisica, Università di
Roma Tre, I-00146 Roma, Italy  INFN Sezione di Roma Tre, I-00146 Roma, Italy
M. Campajola  Dipartimento di Scienze Fisiche, Università di Napoli Federico
II, I-80126 Napoli, Italy  INFN Sezione di Napoli, I-80126 Napoli, Italy  L.
Cao  University of Bonn, 53115 Bonn, Germany  G. Caria  School of Physics,
University of Melbourne, Victoria 3010, Australia  G. Casarosa  Dipartimento
di Fisica, Università di Pisa, I-56127 Pisa, Italy  INFN Sezione di Pisa,
I-56127 Pisa, Italy  C. Cecchi  Dipartimento di Fisica, Università di Perugia,
I-06123 Perugia, Italy  INFN Sezione di Perugia, I-06123 Perugia, Italy  D.
Červenkov  Faculty of Mathematics and Physics, Charles University, 121 16
Prague, Czech Republic  M.-C. Chang  Department of Physics, Fu Jen Catholic
University, Taipei 24205, Taiwan  P. Chang  Department of Physics, National
Taiwan University, Taipei 10617, Taiwan  R. Cheaib  University of British
Columbia, Vancouver, British Columbia, V6T 1Z1, Canada  V. Chekelian  Max-
Planck-Institut für Physik, 80805 München, Germany  Y. Q. Chen  University of
Science and Technology of China, Hefei 230026, China  Y.-T. Chen  Department
of Physics, National Taiwan University, Taipei 10617, Taiwan  B. G. Cheon
Department of Physics and Institute of Natural Sciences, Hanyang University,
Seoul 04763, South Korea  K. Chilikin  P.N. Lebedev Physical Institute of the
Russian Academy of Sciences, Moscow 119991, Russian Federation  H.-E. Cho
Department of Physics and Institute of Natural Sciences, Hanyang University,
Seoul 04763, South Korea  K. Cho  Korea Institute of Science and Technology
Information, Daejeon 34141, South Korea  S.-J. Cho  Yonsei University, Seoul
03722, South Korea  S.-K. Choi  Gyeongsang National University, Jinju 52828,
South Korea  S. Choudhury  Indian Institute of Technology Hyderabad, Telangana
502285, India  D. Cinabro  Wayne State University, Detroit, Michigan 48202,
U.S.A.  L. Corona  Dipartimento di Fisica, Università di Pisa, I-56127 Pisa,
Italy  INFN Sezione di Pisa, I-56127 Pisa, Italy  L. M. Cremaldi  University
of Mississippi, University, Mississippi 38677, U.S.A.  D. Cuesta  Université
de Strasbourg, CNRS, IPHC, UMR 7178, 67037 Strasbourg, France  S. Cunliffe
Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  T. Czank  Kavli
Institute for the Physics and Mathematics of the Universe (WPI), University of
Tokyo, Kashiwa 277-8583, Japan  N. Dash  Indian Institute of Technology
Madras, Chennai 600036, India  F. Dattola  Deutsches Elektronen–Synchrotron,
22607 Hamburg, Germany  E. De La Cruz-Burelo  Centro de Investigacion y de
Estudios Avanzados del Instituto Politecnico Nacional, Mexico City 07360,
Mexico  Consejo Nacional de Ciencia y Tecnología, Mexico City 03940, Mexico
G. De Nardo  Dipartimento di Scienze Fisiche, Università di Napoli Federico
II, I-80126 Napoli, Italy  INFN Sezione di Napoli, I-80126 Napoli, Italy  M.
De Nuccio  Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  G. De
Pietro  INFN Sezione di Roma Tre, I-00146 Roma, Italy  R. de Sangro  INFN
Laboratori Nazionali di Frascati, I-00044 Frascati, Italy  B. Deschamps
University of Bonn, 53115 Bonn, Germany  M. Destefanis  Dipartimento di
Fisica, Università di Torino, I-10125 Torino, Italy  INFN Sezione di Torino,
I-10125 Torino, Italy  S. Dey  Tel Aviv University, School of Physics and
Astronomy, Tel Aviv, 69978, Israel  A. De Yta-Hernandez  Centro de
Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional,
Mexico City 07360, Mexico  F. Di Capua  Dipartimento di Scienze Fisiche,
Università di Napoli Federico II, I-80126 Napoli, Italy  INFN Sezione di
Napoli, I-80126 Napoli, Italy  S. Di Carlo  Université Paris-Saclay,
CNRS/IN2P3, IJCLab, 91405 Orsay, France  J. Dingfelder  University of Bonn,
53115 Bonn, Germany  Z. Doležal  Faculty of Mathematics and Physics, Charles
University, 121 16 Prague, Czech Republic  I. Domínguez Jiménez  Universidad
Autonoma de Sinaloa, Sinaloa 80000, Mexico  T. V. Dong  Key Laboratory of
Nuclear Physics and Ion-beam Application (MOE) and Institute of Modern
Physics, Fudan University, Shanghai 200443, China  K. Dort  Justus-Liebig-
Universität Gießen, 35392 Gießen, Germany  D. Dossett  School of Physics,
University of Melbourne, Victoria 3010, Australia  S. Dubey  University of
Hawaii, Honolulu, Hawaii 96822, U.S.A.  S. Duell  University of Bonn, 53115
Bonn, Germany  G. Dujany  Université de Strasbourg, CNRS, IPHC, UMR 7178,
67037 Strasbourg, France  S. Eidelman  Budker Institute of Nuclear Physics SB
RAS, Novosibirsk 630090, Russian Federation  P.N. Lebedev Physical Institute
of the Russian Academy of Sciences, Moscow 119991, Russian Federation
Novosibirsk State University, Novosibirsk 630090, Russian Federation  M.
Eliachevitch  University of Bonn, 53115 Bonn, Germany  D. Epifanov  Budker
Institute of Nuclear Physics SB RAS, Novosibirsk 630090, Russian Federation
Novosibirsk State University, Novosibirsk 630090, Russian Federation  J. E.
Fast  Pacific Northwest National Laboratory, Richland, Washington 99352,
U.S.A.  T. Ferber  Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany
D. Ferlewicz  School of Physics, University of Melbourne, Victoria 3010,
Australia  G. Finocchiaro  INFN Laboratori Nazionali di Frascati, I-00044
Frascati, Italy  S. Fiore  INFN Sezione di Roma, I-00185 Roma, Italy  P.
Fischer  University of Heidelberg, 68131 Mannheim, Germany  A. Fodor  McGill
University, Montréal, Québec, H3A 2T8, Canada  F. Forti  Dipartimento di
Fisica, Università di Pisa, I-56127 Pisa, Italy  INFN Sezione di Pisa, I-56127
Pisa, Italy  A. Frey  II. Physikalisches Institut, Georg-August-Universität
Göttingen, 37073 Göttingen, Germany  M. Friedl  Institute of High Energy
Physics, Vienna 1050, Austria  B. G. Fulsom  Pacific Northwest National
Laboratory, Richland, Washington 99352, U.S.A.  M. Gabriel  Max-Planck-
Institut für Physik, 80805 München, Germany  N. Gabyshev  Budker Institute of
Nuclear Physics SB RAS, Novosibirsk 630090, Russian Federation  Novosibirsk
State University, Novosibirsk 630090, Russian Federation  E. Ganiev
Dipartimento di Fisica, Università di Trieste, I-34127 Trieste, Italy  INFN
Sezione di Trieste, I-34127 Trieste, Italy  M. Garcia-Hernandez  Centro de
Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional,
Mexico City 07360, Mexico  R. Garg  Panjab University, Chandigarh 160014,
India  A. Garmash  Budker Institute of Nuclear Physics SB RAS, Novosibirsk
630090, Russian Federation  Novosibirsk State University, Novosibirsk 630090,
Russian Federation  V. Gaur  Virginia Polytechnic Institute and State
University, Blacksburg, Virginia 24061, U.S.A.  A. Gaz  Graduate School of
Science, Nagoya University, Nagoya 464-8602, Japan  Kobayashi-Maskawa
Institute, Nagoya University, Nagoya 464-8602, Japan  U. Gebauer  II.
Physikalisches Institut, Georg-August-Universität Göttingen, 37073 Göttingen,
Germany  M. Gelb  Institut für Experimentelle Teilchenphysik, Karlsruher
Institut für Technologie, 76131 Karlsruhe, Germany  A. Gellrich  Deutsches
Elektronen–Synchrotron, 22607 Hamburg, Germany  J. Gemmler  Institut für
Experimentelle Teilchenphysik, Karlsruher Institut für Technologie, 76131
Karlsruhe, Germany  T. Geßler  Justus-Liebig-Universität Gießen, 35392 Gießen,
Germany  D. Getzkow  Justus-Liebig-Universität Gießen, 35392 Gießen, Germany
R. Giordano  Dipartimento di Scienze Fisiche, Università di Napoli Federico
II, I-80126 Napoli, Italy  INFN Sezione di Napoli, I-80126 Napoli, Italy  A.
Giri  Indian Institute of Technology Hyderabad, Telangana 502285, India  A.
Glazov  Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  B. Gobbo
INFN Sezione di Trieste, I-34127 Trieste, Italy  R. Godang  University of
South Alabama, Mobile, Alabama 36688, U.S.A.  P. Goldenzweig  Institut für
Experimentelle Teilchenphysik, Karlsruher Institut für Technologie, 76131
Karlsruhe, Germany  B. Golob  Faculty of Mathematics and Physics, University
of Ljubljana, 1000 Ljubljana, Slovenia  J. Stefan Institute, 1000 Ljubljana,
Slovenia  P. Gomis  Instituto de Fisica Corpuscular, Paterna 46980, Spain  P.
Grace  Department of Physics, University of Adelaide, Adelaide, South
Australia 5005, Australia  W. Gradl  Johannes Gutenberg-Universität Mainz,
Institut für Kernphysik, D-55099 Mainz, Germany  E. Graziani  INFN Sezione di
Roma Tre, I-00146 Roma, Italy  D. Greenwald  Department of Physics, Technische
Universität München, 85748 Garching, Germany  Y. Guan  University of
Cincinnati, Cincinnati, Ohio 45221, U.S.A.  C. Hadjivasiliou  Pacific
Northwest National Laboratory, Richland, Washington 99352, U.S.A.  S. Halder
Tata Institute of Fundamental Research, Mumbai 400005, India  K. Hara  High
Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The
Graduate University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan
T. Hara  High Energy Accelerator Research Organization (KEK), Tsukuba
305-0801, Japan  The Graduate University for Advanced Studies (SOKENDAI),
Hayama 240-0193, Japan  O. Hartbrich  University of Hawaii, Honolulu, Hawaii
96822, U.S.A.  T. Hauth  Institut für Experimentelle Teilchenphysik,
Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany  K. Hayasaka
Niigata University, Niigata 950-2181, Japan  H. Hayashii  Nara Women’s
University, Nara 630-8506, Japan  C. Hearty  University of British Columbia,
Vancouver, British Columbia, V6T 1Z1, Canada  Institute of Particle Physics
(Canada), Victoria, British Columbia V8W 2Y2, Canada  M. Heck  Institut für
Experimentelle Teilchenphysik, Karlsruher Institut für Technologie, 76131
Karlsruhe, Germany  M. T. Hedges  University of Hawaii, Honolulu, Hawaii
96822, U.S.A.  I. Heredia de la Cruz  Centro de Investigacion y de Estudios
Avanzados del Instituto Politecnico Nacional, Mexico City 07360, Mexico
Consejo Nacional de Ciencia y Tecnología, Mexico City 03940, Mexico  M.
Hernández Villanueva  University of Mississippi, University, Mississippi
38677, U.S.A.  A. Hershenhorn  University of British Columbia, Vancouver,
British Columbia, V6T 1Z1, Canada  T. Higuchi  Kavli Institute for the Physics
and Mathematics of the Universe (WPI), University of Tokyo, Kashiwa 277-8583,
Japan  E. C. Hill  University of British Columbia, Vancouver, British
Columbia, V6T 1Z1, Canada  H. Hirata  Graduate School of Science, Nagoya
University, Nagoya 464-8602, Japan  S. Hirose  Graduate School of Science,
Nagoya University, Nagoya 464-8602, Japan  M. Hoek  Johannes Gutenberg-
Universität Mainz, Institut für Kernphysik, D-55099 Mainz, Germany  M. Hohmann
School of Physics, University of Melbourne, Victoria 3010, Australia  S.
Hollitt  Department of Physics, University of Adelaide, Adelaide, South
Australia 5005, Australia  T. Hotta  Research Center for Nuclear Physics,
Osaka University, Osaka 567-0047, Japan  C.-L. Hsu  School of Physics,
University of Sydney, New South Wales 2006, Australia  Y. Hu  Institute of
High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China  K.
Huang  Department of Physics, National Taiwan University, Taipei 10617, Taiwan
T. Iijima  Graduate School of Science, Nagoya University, Nagoya 464-8602,
Japan  Kobayashi-Maskawa Institute, Nagoya University, Nagoya 464-8602, Japan
K. Inami  Graduate School of Science, Nagoya University, Nagoya 464-8602,
Japan  G. Inguglia  Institute of High Energy Physics, Vienna 1050, Austria  J.
Irakkathil Jabbar  Institut für Experimentelle Teilchenphysik, Karlsruher
Institut für Technologie, 76131 Karlsruhe, Germany  A. Ishikawa  High Energy
Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The Graduate
University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan  R. Itoh
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
The Graduate University for Advanced Studies (SOKENDAI), Hayama 240-0193,
Japan  M. Iwasaki  Osaka City University, Osaka 558-8585, Japan  Y. Iwasaki
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
S. Iwata  Tokyo Metropolitan University, Tokyo 192-0397, Japan  P. Jackson
Department of Physics, University of Adelaide, Adelaide, South Australia 5005,
Australia  W. W. Jacobs  Indiana University, Bloomington, Indiana 47408,
U.S.A.  I. Jaegle  University of Florida, Gainesville, Florida 32611, U.S.A.
D. E. Jaffe  Brookhaven National Laboratory, Upton, New York 11973, U.S.A.
E.-J. Jang  Gyeongsang National University, Jinju 52828, South Korea  M.
Jeandron  University of Mississippi, University, Mississippi 38677, U.S.A.  H.
B. Jeon  Kyungpook National University, Daegu 41566, South Korea  S. Jia
Beihang University, Beijing 100191, China  Y. Jin  INFN Sezione di Trieste,
I-34127 Trieste, Italy  C. Joo  Kavli Institute for the Physics and
Mathematics of the Universe (WPI), University of Tokyo, Kashiwa 277-8583,
Japan  K. K. Joo  Chonnam National University, Gwangju 61186, South Korea  I.
Kadenko  Taras Shevchenko National Univ. of Kiev, Kiev, Ukraine  J. Kahn
Institut für Experimentelle Teilchenphysik, Karlsruher Institut für
Technologie, 76131 Karlsruhe, Germany  H. Kakuno  Tokyo Metropolitan
University, Tokyo 192-0397, Japan  A. B. Kaliyar  Tata Institute of
Fundamental Research, Mumbai 400005, India  J. Kandra  Faculty of Mathematics
and Physics, Charles University, 121 16 Prague, Czech Republic  K. H. Kang
Kyungpook National University, Daegu 41566, South Korea  P. Kapusta  H.
Niewodniczanski Institute of Nuclear Physics, Krakow 31-342, Poland  G. Karyan
Alikhanyan National Science Laboratory, Yerevan 0036, Armenia  Y. Kato
Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
Kobayashi-Maskawa Institute, Nagoya University, Nagoya 464-8602, Japan  H.
Kawai  Chiba University, Chiba 263-8522, Japan  T. Kawasaki  Kitasato
University, Sagamihara 252-0373, Japan  T. Keck  Institut für Experimentelle
Teilchenphysik, Karlsruher Institut für Technologie, 76131 Karlsruhe, Germany
C. Ketter  University of Hawaii, Honolulu, Hawaii 96822, U.S.A.  H. Kichimi
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
C. Kiesling  Max-Planck-Institut für Physik, 80805 München, Germany  B. H. Kim
Seoul National University, Seoul 08826, South Korea  C.-H. Kim  Department of
Physics and Institute of Natural Sciences, Hanyang University, Seoul 04763,
South Korea  D. Y. Kim  Soongsil University, Seoul 06978, South Korea  H. J.
Kim  Kyungpook National University, Daegu 41566, South Korea  J. B. Kim  Korea
University, Seoul 02841, South Korea  K.-H. Kim  Yonsei University, Seoul
03722, South Korea  K. Kim  Korea University, Seoul 02841, South Korea  S.-H.
Kim  Seoul National University, Seoul 08826, South Korea  Y.-K. Kim  Yonsei
University, Seoul 03722, South Korea  Y. Kim  Korea University, Seoul 02841,
South Korea  T. D. Kimmel  Virginia Polytechnic Institute and State
University, Blacksburg, Virginia 24061, U.S.A.  H. Kindo  High Energy
Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The Graduate
University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan  K.
Kinoshita  University of Cincinnati, Cincinnati, Ohio 45221, U.S.A.  B. Kirby
Brookhaven National Laboratory, Upton, New York 11973, U.S.A.  C. Kleinwort
Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  B. Knysh  Université
Paris-Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France  P. Kodyš  Faculty of
Mathematics and Physics, Charles University, 121 16 Prague, Czech Republic  T.
Koga  High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801,
Japan  S. Kohani  University of Hawaii, Honolulu, Hawaii 96822, U.S.A.  S.
Koirala  Department of Physics, National Taiwan University, Taipei 10617,
Taiwan  I. Komarov  Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany
T. Konno  Kitasato University, Sagamihara 252-0373, Japan  S. Korpar
University of Maribor, 2000 Maribor, Slovenia  J. Stefan Institute, 1000
Ljubljana, Slovenia  E. Kou  Université Paris-Saclay, CNRS/IN2P3, IJCLab,
91405 Orsay, France  N. Kovalchuk  Deutsches Elektronen–Synchrotron, 22607
Hamburg, Germany  T. M. G. Kraetzschmar  Max-Planck-Institut für Physik, 80805
München, Germany  P. Križan  Faculty of Mathematics and Physics, University of
Ljubljana, 1000 Ljubljana, Slovenia  J. Stefan Institute, 1000 Ljubljana,
Slovenia  R. Kroeger  University of Mississippi, University, Mississippi
38677, U.S.A.  J. F. Krohn  School of Physics, University of Melbourne,
Victoria 3010, Australia  P. Krokovny  Budker Institute of Nuclear Physics SB
RAS, Novosibirsk 630090, Russian Federation  Novosibirsk State University,
Novosibirsk 630090, Russian Federation  H. Krüger  University of Bonn, 53115
Bonn, Germany  W. Kuehn  Justus-Liebig-Universität Gießen, 35392 Gießen,
Germany  T. Kuhr  Ludwig Maximilians University, 80539 Munich, Germany  J.
Kumar  Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, U.S.A.  M.
Kumar  Malaviya National Institute of Technology Jaipur, Jaipur 302017, India
R. Kumar  Punjab Agricultural University, Ludhiana 141004, India  K. Kumara
Wayne State University, Detroit, Michigan 48202, U.S.A.  T. Kumita  Tokyo
Metropolitan University, Tokyo 192-0397, Japan  T. Kunigo  High Energy
Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  M. Künzel
Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  Ludwig Maximilians
University, 80539 Munich, Germany  S. Kurz  Deutsches Elektronen–Synchrotron,
22607 Hamburg, Germany  A. Kuzmin  Budker Institute of Nuclear Physics SB RAS,
Novosibirsk 630090, Russian Federation  Novosibirsk State University,
Novosibirsk 630090, Russian Federation  P. Kvasnička  Faculty of Mathematics
and Physics, Charles University, 121 16 Prague, Czech Republic  Y.-J. Kwon
Yonsei University, Seoul 03722, South Korea  S. Lacaprara  INFN Sezione di
Padova, I-35131 Padova, Italy  Y.-T. Lai  High Energy Accelerator Research
Organization (KEK), Tsukuba 305-0801, Japan  C. La Licata  Kavli Institute for
the Physics and Mathematics of the Universe (WPI), University of Tokyo,
Kashiwa 277-8583, Japan  K. Lalwani  Malaviya National Institute of Technology
Jaipur, Jaipur 302017, India  L. Lanceri  INFN Sezione di Trieste, I-34127
Trieste, Italy  J. S. Lange  Justus-Liebig-Universität Gießen, 35392 Gießen,
Germany  K. Lautenbach  Justus-Liebig-Universität Gießen, 35392 Gießen,
Germany  P. J. Laycock  Brookhaven National Laboratory, Upton, New York 11973,
U.S.A.  F. R. Le Diberder  Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405
Orsay, France  I.-S. Lee  Department of Physics and Institute of Natural
Sciences, Hanyang University, Seoul 04763, South Korea  S. C. Lee  Kyungpook
National University, Daegu 41566, South Korea  P. Leitl  Max-Planck-Institut
für Physik, 80805 München, Germany  D. Levit  Department of Physics,
Technische Universität München, 85748 Garching, Germany  P. M. Lewis
University of Bonn, 53115 Bonn, Germany  C. Li  Liaoning Normal University,
Dalian 116029, China  L. K. Li  University of Cincinnati, Cincinnati, Ohio
45221, U.S.A.  S. X. Li  Beihang University, Beijing 100191, China  Y. M. Li
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049,
China  Y. B. Li  Peking University, Beijing 100871, China  J. Libby  Indian
Institute of Technology Madras, Chennai 600036, India  K. Lieret  Ludwig
Maximilians University, 80539 Munich, Germany  L. Li Gioi  Max-Planck-Institut
für Physik, 80805 München, Germany  J. Lin  Department of Physics, National
Taiwan University, Taipei 10617, Taiwan  Z. Liptak  University of Hawaii,
Honolulu, Hawaii 96822, U.S.A.  Q. Y. Liu  Key Laboratory of Nuclear Physics
and Ion-beam Application (MOE) and Institute of Modern Physics, Fudan
University, Shanghai 200443, China  Z. A. Liu  Institute of High Energy
Physics, Chinese Academy of Sciences, Beijing 100049, China  D. Liventsev
Wayne State University, Detroit, Michigan 48202, U.S.A.  High Energy
Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  S. Longo
Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  A. Loos  University
of South Carolina, Columbia, South Carolina 29208, U.S.A.  P. Lu  Department
of Physics, National Taiwan University, Taipei 10617, Taiwan  M. Lubej  J.
Stefan Institute, 1000 Ljubljana, Slovenia  T. Lueck  Ludwig Maximilians
University, 80539 Munich, Germany  F. Luetticke  University of Bonn, 53115
Bonn, Germany  T. Luo  Key Laboratory of Nuclear Physics and Ion-beam
Application (MOE) and Institute of Modern Physics, Fudan University, Shanghai
200443, China  C. MacQueen  School of Physics, University of Melbourne,
Victoria 3010, Australia  Y. Maeda  Graduate School of Science, Nagoya
University, Nagoya 464-8602, Japan  Kobayashi-Maskawa Institute, Nagoya
University, Nagoya 464-8602, Japan  M. Maggiora  Dipartimento di Fisica,
Università di Torino, I-10125 Torino, Italy  INFN Sezione di Torino, I-10125
Torino, Italy  S. Maity  Indian Institute of Technology Bhubaneswar, Satya
Nagar 751007, India  R. Manfredi  Dipartimento di Fisica, Università di
Trieste, I-34127 Trieste, Italy  INFN Sezione di Trieste, I-34127 Trieste,
Italy  E. Manoni  INFN Sezione di Perugia, I-06123 Perugia, Italy  S. Marcello
Dipartimento di Fisica, Università di Torino, I-10125 Torino, Italy  INFN
Sezione di Torino, I-10125 Torino, Italy  C. Marinas  Instituto de Fisica
Corpuscular, Paterna 46980, Spain  A. Martini  Dipartimento di Matematica e
Fisica, Università di Roma Tre, I-00146 Roma, Italy  INFN Sezione di Roma Tre,
I-00146 Roma, Italy  M. Masuda  Earthquake Research Institute, University of
Tokyo, Tokyo 113-0032, Japan  Research Center for Nuclear Physics, Osaka
University, Osaka 567-0047, Japan  T. Matsuda  University of Miyazaki,
Miyazaki 889-2192, Japan  K. Matsuoka  Graduate School of Science, Nagoya
University, Nagoya 464-8602, Japan  Kobayashi-Maskawa Institute, Nagoya
University, Nagoya 464-8602, Japan  D. Matvienko  Budker Institute of Nuclear
Physics SB RAS, Novosibirsk 630090, Russian Federation  P.N. Lebedev Physical
Institute of the Russian Academy of Sciences, Moscow 119991, Russian
Federation  Novosibirsk State University, Novosibirsk 630090, Russian
Federation  J. McNeil  University of Florida, Gainesville, Florida 32611,
U.S.A.  F. Meggendorfer  Max-Planck-Institut für Physik, 80805 München,
Germany  J. C. Mei  Key Laboratory of Nuclear Physics and Ion-beam Application
(MOE) and Institute of Modern Physics, Fudan University, Shanghai 200443,
China  F. Meier  Duke University, Durham, North Carolina 27708, U.S.A.  M.
Merola  Dipartimento di Scienze Fisiche, Università di Napoli Federico II,
I-80126 Napoli, Italy  INFN Sezione di Napoli, I-80126 Napoli, Italy  F.
Metzner  Institut für Experimentelle Teilchenphysik, Karlsruher Institut für
Technologie, 76131 Karlsruhe, Germany  M. Milesi  School of Physics,
University of Melbourne, Victoria 3010, Australia  C. Miller  University of
Victoria, Victoria, British Columbia, V8W 3P6, Canada  K. Miyabayashi  Nara
Women’s University, Nara 630-8506, Japan  H. Miyake  High Energy Accelerator
Research Organization (KEK), Tsukuba 305-0801, Japan  The Graduate University
for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan  H. Miyata  Niigata
University, Niigata 950-2181, Japan  R. Mizuk  P.N. Lebedev Physical Institute
of the Russian Academy of Sciences, Moscow 119991, Russian Federation  Higher
School of Economics (HSE), Moscow 101000, Russian Federation  K. Azmi
National Centre for Particle Physics, University Malaya, 50603 Kuala Lumpur,
Malaysia  G. B. Mohanty  Tata Institute of Fundamental Research, Mumbai
400005, India  H. Moon  Korea University, Seoul 02841, South Korea  T. Moon
Seoul National University, Seoul 08826, South Korea  J. A. Mora Grimaldo
Department of Physics, University of Tokyo, Tokyo 113-0033, Japan  A. Morda
INFN Sezione di Padova, I-35131 Padova, Italy  T. Morii  Kavli Institute for
the Physics and Mathematics of the Universe (WPI), University of Tokyo,
Kashiwa 277-8583, Japan  H.-G. Moser  Max-Planck-Institut für Physik, 80805
München, Germany  M. Mrvar  Institute of High Energy Physics, Vienna 1050,
Austria  F. Mueller  Max-Planck-Institut für Physik, 80805 München, Germany
F. J. Müller  Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  Th.
Muller  Institut für Experimentelle Teilchenphysik, Karlsruher Institut für
Technologie, 76131 Karlsruhe, Germany  G. Muroyama  Graduate School of
Science, Nagoya University, Nagoya 464-8602, Japan  R. Mussa  INFN Sezione di
Torino, I-10125 Torino, Italy  K. Nakagiri  High Energy Accelerator Research
Organization (KEK), Tsukuba 305-0801, Japan  I. Nakamura  High Energy
Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The Graduate
University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan  K. R.
Nakamura  High Energy Accelerator Research Organization (KEK), Tsukuba
305-0801, Japan  The Graduate University for Advanced Studies (SOKENDAI),
Hayama 240-0193, Japan  E. Nakano  Osaka City University, Osaka 558-8585,
Japan  M. Nakao  High Energy Accelerator Research Organization (KEK), Tsukuba
305-0801, Japan  The Graduate University for Advanced Studies (SOKENDAI),
Hayama 240-0193, Japan  H. Nakayama  High Energy Accelerator Research
Organization (KEK), Tsukuba 305-0801, Japan  The Graduate University for
Advanced Studies (SOKENDAI), Hayama 240-0193, Japan  H. Nakazawa  Department
of Physics, National Taiwan University, Taipei 10617, Taiwan  T. Nanut  J.
Stefan Institute, 1000 Ljubljana, Slovenia  Z. Natkaniec  H. Niewodniczanski
Institute of Nuclear Physics, Krakow 31-342, Poland  M. Nayak  Tel Aviv
University, School of Physics and Astronomy, Tel Aviv, 69978, Israel  G.
Nazaryan  Alikhanyan National Science Laboratory, Yerevan 0036, Armenia  D.
Neverov  Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
C. Niebuhr  Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  M.
Niiyama  Kyoto Sangyo University, Kyoto 603-8555, Japan  J. Ninkovic
Semiconductor Laboratory of the Max Planck Society, 81739 München, Germany  N.
K. Nisar  Brookhaven National Laboratory, Upton, New York 11973, U.S.A.  S.
Nishida  High Energy Accelerator Research Organization (KEK), Tsukuba
305-0801, Japan  The Graduate University for Advanced Studies (SOKENDAI),
Hayama 240-0193, Japan  K. Nishimura  University of Hawaii, Honolulu, Hawaii
96822, U.S.A.  M. Nishimura  High Energy Accelerator Research Organization
(KEK), Tsukuba 305-0801, Japan  M. H. A. Nouxman  National Centre for Particle
Physics, University Malaya, 50603 Kuala Lumpur, Malaysia  B. Oberhof  INFN
Laboratori Nazionali di Frascati, I-00044 Frascati, Italy  K. Ogawa  Niigata
University, Niigata 950-2181, Japan  S. Ogawa  Toho University, Funabashi
274-8510, Japan  S. L. Olsen  Gyeongsang National University, Jinju 52828,
South Korea  Y. Onishchuk  Taras Shevchenko National Univ. of Kiev, Kiev,
Ukraine  H. Ono  Niigata University, Niigata 950-2181, Japan  Y. Onuki
Department of Physics, University of Tokyo, Tokyo 113-0033, Japan  P. Oskin
P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow
119991, Russian Federation  E. R. Oxford  Carnegie Mellon University,
Pittsburgh, Pennsylvania 15213, U.S.A.  H. Ozaki  High Energy Accelerator
Research Organization (KEK), Tsukuba 305-0801, Japan  The Graduate University
for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan  P. Pakhlov  P.N.
Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991,
Russian Federation  Moscow Physical Engineering Institute, Moscow 115409,
Russian Federation  G. Pakhlova  Higher School of Economics (HSE), Moscow
101000, Russian Federation  P.N. Lebedev Physical Institute of the Russian
Academy of Sciences, Moscow 119991, Russian Federation  A. Paladino
Dipartimento di Fisica, Università di Pisa, I-56127 Pisa, Italy  INFN Sezione
di Pisa, I-56127 Pisa, Italy  T. Pang  University of Pittsburgh, Pittsburgh,
Pennsylvania 15260, U.S.A.  A. Panta  University of Mississippi, University,
Mississippi 38677, U.S.A.  E. Paoloni  Dipartimento di Fisica, Università di
Pisa, I-56127 Pisa, Italy  INFN Sezione di Pisa, I-56127 Pisa, Italy  C. Park
Yonsei University, Seoul 03722, South Korea  H. Park  Kyungpook National
University, Daegu 41566, South Korea  S.-H. Park  Yonsei University, Seoul
03722, South Korea  B. Paschen  University of Bonn, 53115 Bonn, Germany  A.
Passeri  INFN Sezione di Roma Tre, I-00146 Roma, Italy  A. Pathak  University
of Louisville, Louisville, Kentucky 40292, U.S.A.  S. Patra  Indian Institute
of Science Education and Research Mohali, SAS Nagar, 140306, India  S. Paul
Department of Physics, Technische Universität München, 85748 Garching, Germany
T. K. Pedlar  Luther College, Decorah, Iowa 52101, U.S.A.  I. Peruzzi  INFN
Laboratori Nazionali di Frascati, I-00044 Frascati, Italy  R. Peschke
University of Hawaii, Honolulu, Hawaii 96822, U.S.A.  R. Pestotnik  J. Stefan
Institute, 1000 Ljubljana, Slovenia  M. Piccolo  INFN Laboratori Nazionali di
Frascati, I-00044 Frascati, Italy  L. E. Piilonen  Virginia Polytechnic
Institute and State University, Blacksburg, Virginia 24061, U.S.A.  P. L. M.
Podesta-Lerma  Universidad Autonoma de Sinaloa, Sinaloa 80000, Mexico  V.
Popov  Higher School of Economics (HSE), Moscow 101000, Russian Federation  C.
Praz  Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  E. Prencipe
Forschungszentrum Jülich, 52425 Jülich, Germany  M. T. Prim  Institut für
Experimentelle Teilchenphysik, Karlsruher Institut für Technologie, 76131
Karlsruhe, Germany  M. V. Purohit  Okinawa Institute of Science and
Technology, Okinawa 904-0495, Japan  P. Rados  Deutsches
Elektronen–Synchrotron, 22607 Hamburg, Germany  R. Rasheed  Université de
Strasbourg, CNRS, IPHC, UMR 7178, 67037 Strasbourg, France  M. Reif  Max-
Planck-Institut für Physik, 80805 München, Germany  S. Reiter  Justus-Liebig-
Universität Gießen, 35392 Gießen, Germany  M. Remnev  Budker Institute of
Nuclear Physics SB RAS, Novosibirsk 630090, Russian Federation  Novosibirsk
State University, Novosibirsk 630090, Russian Federation  P. K. Resmi  Indian
Institute of Technology Madras, Chennai 600036, India  I. Ripp-Baudot
Université de Strasbourg, CNRS, IPHC, UMR 7178, 67037 Strasbourg, France  M.
Ritter  Ludwig Maximilians University, 80539 Munich, Germany  M. Ritzert
University of Heidelberg, 68131 Mannheim, Germany  G. Rizzo  Dipartimento di
Fisica, Università di Pisa, I-56127 Pisa, Italy  INFN Sezione di Pisa, I-56127
Pisa, Italy  L. B. Rizzuto  J. Stefan Institute, 1000 Ljubljana, Slovenia  S.
H. Robertson  McGill University, Montréal, Québec, H3A 2T8, Canada  Institute
of Particle Physics (Canada), Victoria, British Columbia V8W 2Y2, Canada  D.
Rodríguez Pérez  Universidad Autonoma de Sinaloa, Sinaloa 80000, Mexico  J. M.
Roney  University of Victoria, Victoria, British Columbia, V8W 3P6, Canada
Institute of Particle Physics (Canada), Victoria, British Columbia V8W 2Y2,
Canada  C. Rosenfeld  University of South Carolina, Columbia, South Carolina
29208, U.S.A.  A. Rostomyan  Deutsches Elektronen–Synchrotron, 22607 Hamburg,
Germany  N. Rout  Indian Institute of Technology Madras, Chennai 600036, India
M. Rozanska  H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342,
Poland  S. Rummel  Ludwig Maximilians University, 80539 Munich, Germany  G.
Russo  Dipartimento di Scienze Fisiche, Università di Napoli Federico II,
I-80126 Napoli, Italy  INFN Sezione di Napoli, I-80126 Napoli, Italy  D. Sahoo
Tata Institute of Fundamental Research, Mumbai 400005, India  Y. Sakai  High
Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The
Graduate University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan
D. A. Sanders  University of Mississippi, University, Mississippi 38677,
U.S.A.  S. Sandilya  University of Cincinnati, Cincinnati, Ohio 45221, U.S.A.
A. Sangal  University of Cincinnati, Cincinnati, Ohio 45221, U.S.A.  L.
Santelj  Faculty of Mathematics and Physics, University of Ljubljana, 1000
Ljubljana, Slovenia  J. Stefan Institute, 1000 Ljubljana, Slovenia  P. Sartori
Dipartimento di Fisica e Astronomia, Università di Padova, I-35131 Padova,
Italy  INFN Sezione di Padova, I-35131 Padova, Italy  J. Sasaki  Department of
Physics, University of Tokyo, Tokyo 113-0033, Japan  Y. Sato  Department of
Physics, Tohoku University, Sendai 980-8578, Japan  V. Savinov  University of
Pittsburgh, Pittsburgh, Pennsylvania 15260, U.S.A.  B. Scavino  Johannes
Gutenberg-Universität Mainz, Institut für Kernphysik, D-55099 Mainz, Germany
M. Schram  Pacific Northwest National Laboratory, Richland, Washington 99352,
U.S.A.  H. Schreeck  II. Physikalisches Institut, Georg-August-Universität
Göttingen, 37073 Göttingen, Germany  J. Schueler  University of Hawaii,
Honolulu, Hawaii 96822, U.S.A.  C. Schwanda  Institute of High Energy Physics,
Vienna 1050, Austria  A. J. Schwartz  University of Cincinnati, Cincinnati,
Ohio 45221, U.S.A.  B. Schwenker  II. Physikalisches Institut, Georg-August-
Universität Göttingen, 37073 Göttingen, Germany  R. M. Seddon  McGill
University, Montréal, Québec, H3A 2T8, Canada  Y. Seino  Niigata University,
Niigata 950-2181, Japan  A. Selce  University of Bonn, 53115 Bonn, Germany  K.
Senyo  Yamagata University, Yamagata 990-8560, Japan  I. S. Seong  University
of Hawaii, Honolulu, Hawaii 96822, U.S.A.  M. E. Sevior  School of Physics,
University of Melbourne, Victoria 3010, Australia  C. Sfienti  Johannes
Gutenberg-Universität Mainz, Institut für Kernphysik, D-55099 Mainz, Germany
V. Shebalin  University of Hawaii, Honolulu, Hawaii 96822, U.S.A.  C. P. Shen
Beihang University, Beijing 100191, China  H. Shibuya  Toho University,
Funabashi 274-8510, Japan  J.-G. Shiu  Department of Physics, National Taiwan
University, Taipei 10617, Taiwan  B. Shwartz  Budker Institute of Nuclear
Physics SB RAS, Novosibirsk 630090, Russian Federation  Novosibirsk State
University, Novosibirsk 630090, Russian Federation  A. Sibidanov  University
of Victoria, Victoria, British Columbia, V8W 3P6, Canada  F. Simon  Max-
Planck-Institut für Physik, 80805 München, Germany  J. B. Singh  Panjab
University, Chandigarh 160014, India  S. Skambraks  Max-Planck-Institut für
Physik, 80805 München, Germany  K. Smith  School of Physics, University of
Melbourne, Victoria 3010, Australia  R. J. Sobie  University of Victoria,
Victoria, British Columbia, V8W 3P6, Canada  Institute of Particle Physics
(Canada), Victoria, British Columbia V8W 2Y2, Canada  A. Soffer  Tel Aviv
University, School of Physics and Astronomy, Tel Aviv, 69978, Israel  A.
Sokolov  Institute for High Energy Physics, Protvino 142281, Russian
Federation  Y. Soloviev  Deutsches Elektronen–Synchrotron, 22607 Hamburg,
Germany  E. Solovieva  P.N. Lebedev Physical Institute of the Russian Academy
of Sciences, Moscow 119991, Russian Federation  S. Spataro  Dipartimento di
Fisica, Università di Torino, I-10125 Torino, Italy  INFN Sezione di Torino,
I-10125 Torino, Italy  B. Spruck  Johannes Gutenberg-Universität Mainz,
Institut für Kernphysik, D-55099 Mainz, Germany  M. Starič  J. Stefan
Institute, 1000 Ljubljana, Slovenia  S. Stefkova  Deutsches
Elektronen–Synchrotron, 22607 Hamburg, Germany  Z. S. Stottler  Virginia
Polytechnic Institute and State University, Blacksburg, Virginia 24061, U.S.A.
R. Stroili  Dipartimento di Fisica e Astronomia, Università di Padova, I-35131
Padova, Italy  INFN Sezione di Padova, I-35131 Padova, Italy  J. Strube
Pacific Northwest National Laboratory, Richland, Washington 99352, U.S.A.  J.
Stypula  H. Niewodniczanski Institute of Nuclear Physics, Krakow 31-342,
Poland  M. Sumihama  Gifu University, Gifu 501-1193, Japan  Research Center
for Nuclear Physics, Osaka University, Osaka 567-0047, Japan  K. Sumisawa
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
The Graduate University for Advanced Studies (SOKENDAI), Hayama 240-0193,
Japan  T. Sumiyoshi  Tokyo Metropolitan University, Tokyo 192-0397, Japan  D.
J. Summers  University of Mississippi, University, Mississippi 38677, U.S.A.
W. Sutcliffe  University of Bonn, 53115 Bonn, Germany  K. Suzuki  Graduate
School of Science, Nagoya University, Nagoya 464-8602, Japan  S. Y. Suzuki
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
The Graduate University for Advanced Studies (SOKENDAI), Hayama 240-0193,
Japan  M. Tabata  Chiba University, Chiba 263-8522, Japan  M. Takahashi
Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  M. Takizawa
Theoretical Research Division, Nishina Center, RIKEN, Saitama 351-0198, Japan
J-PARC Branch, KEK Theory Center, High Energy Accelerator Research
Organization (KEK), Tsukuba 305-0801, Japan  Showa Pharmaceutical University,
Tokyo 194-8543, Japan  U. Tamponi  INFN Sezione di Torino, I-10125 Torino,
Italy  S. Tanaka  High Energy Accelerator Research Organization (KEK), Tsukuba
305-0801, Japan  The Graduate University for Advanced Studies (SOKENDAI),
Hayama 240-0193, Japan  K. Tanida  Advanced Science Research Center, Japan
Atomic Energy Agency, Naka 319-1195, Japan  H. Tanigawa  Department of
Physics, University of Tokyo, Tokyo 113-0033, Japan  N. Taniguchi  High Energy
Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  Y. Tao
University of Florida, Gainesville, Florida 32611, U.S.A.  P. Taras
Université de Montréal, Physique des Particules, Montréal, Québec, H3C 3J7,
Canada  F. Tenchini  Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany
D. Tonelli  INFN Sezione di Trieste, I-34127 Trieste, Italy  E. Torassa  INFN
Sezione di Padova, I-35131 Padova, Italy  K. Trabelsi  Université Paris-
Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France  T. Tsuboyama  High Energy
Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The Graduate
University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan  N. Tsuzuki
Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan  M.
Uchida  Tokyo Institute of Technology, Tokyo 152-8550, Japan  I. Ueda  High
Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The
Graduate University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan
S. Uehara  High Energy Accelerator Research Organization (KEK), Tsukuba
305-0801, Japan  The Graduate University for Advanced Studies (SOKENDAI),
Hayama 240-0193, Japan  T. Ueno  Department of Physics, Tohoku University,
Sendai 980-8578, Japan  T. Uglov  P.N. Lebedev Physical Institute of the
Russian Academy of Sciences, Moscow 119991, Russian Federation  Higher School
of Economics (HSE), Moscow 101000, Russian Federation  K. Unger  Institut für
Experimentelle Teilchenphysik, Karlsruher Institut für Technologie, 76131
Karlsruhe, Germany  Y. Unno  Department of Physics and Institute of Natural
Sciences, Hanyang University, Seoul 04763, South Korea  S. Uno  High Energy
Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  The Graduate
University for Advanced Studies (SOKENDAI), Hayama 240-0193, Japan  P. Urquijo
School of Physics, University of Melbourne, Victoria 3010, Australia  Y.
Ushiroda  High Energy Accelerator Research Organization (KEK), Tsukuba
305-0801, Japan  The Graduate University for Advanced Studies (SOKENDAI),
Hayama 240-0193, Japan  Department of Physics, University of Tokyo, Tokyo
113-0033, Japan  Y. Usov  Budker Institute of Nuclear Physics SB RAS,
Novosibirsk 630090, Russian Federation  Novosibirsk State University,
Novosibirsk 630090, Russian Federation  S. E. Vahsen  University of Hawaii,
Honolulu, Hawaii 96822, U.S.A.  R. van Tonder  University of Bonn, 53115 Bonn,
Germany  G. S. Varner  University of Hawaii, Honolulu, Hawaii 96822, U.S.A.
K. E. Varvell  School of Physics, University of Sydney, New South Wales 2006,
Australia  A. Vinokurova  Budker Institute of Nuclear Physics SB RAS,
Novosibirsk 630090, Russian Federation  Novosibirsk State University,
Novosibirsk 630090, Russian Federation  L. Vitale  Dipartimento di Fisica,
Università di Trieste, I-34127 Trieste, Italy  INFN Sezione di Trieste,
I-34127 Trieste, Italy  V. Vorobyev  Budker Institute of Nuclear Physics SB
RAS, Novosibirsk 630090, Russian Federation  P.N. Lebedev Physical Institute
of the Russian Academy of Sciences, Moscow 119991, Russian Federation
Novosibirsk State University, Novosibirsk 630090, Russian Federation  A.
Vossen  Duke University, Durham, North Carolina 27708, U.S.A.  E. Waheed  High
Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan  H. M.
Wakeling  McGill University, Montréal, Québec, H3A 2T8, Canada  K. Wan
Department of Physics, University of Tokyo, Tokyo 113-0033, Japan  W. Wan
Abdullah  National Centre for Particle Physics, University Malaya, 50603 Kuala
Lumpur, Malaysia  B. Wang  Max-Planck-Institut für Physik, 80805 München,
Germany  C. H. Wang  National United University, Miao Li 36003, Taiwan  M.-Z.
Wang  Department of Physics, National Taiwan University, Taipei 10617, Taiwan
X. L. Wang  Key Laboratory of Nuclear Physics and Ion-beam Application (MOE)
and Institute of Modern Physics, Fudan University, Shanghai 200443, China  A.
Warburton  McGill University, Montréal, Québec, H3A 2T8, Canada  M. Watanabe
Niigata University, Niigata 950-2181, Japan  S. Watanuki  Université Paris-
Saclay, CNRS/IN2P3, IJCLab, 91405 Orsay, France  I. Watson  Department of
Physics, University of Tokyo, Tokyo 113-0033, Japan  J. Webb  School of
Physics, University of Melbourne, Victoria 3010, Australia  S. Wehle
Deutsches Elektronen–Synchrotron, 22607 Hamburg, Germany  M. Welsch
University of Bonn, 53115 Bonn, Germany  C. Wessel  University of Bonn, 53115
Bonn, Germany  J. Wiechczynski  INFN Sezione di Pisa, I-56127 Pisa, Italy  P.
Wieduwilt  II. Physikalisches Institut, Georg-August-Universität Göttingen,
37073 Göttingen, Germany  H. Windel  Max-Planck-Institut für Physik, 80805
München, Germany  E. Won  Korea University, Seoul 02841, South Korea  L. J. Wu
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049,
China  X. P. Xu  Soochow University, Suzhou 215006, China  B. Yabsley  School
of Physics, University of Sydney, New South Wales 2006, Australia  S. Yamada
High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan
W. Yan  University of Science and Technology of China, Hefei 230026, China  S.
B. Yang  Korea University, Seoul 02841, South Korea  H. Ye  Deutsches
Elektronen–Synchrotron, 22607 Hamburg, Germany  J. Yelton  University of
Florida, Gainesville, Florida 32611, U.S.A.  I. Yeo  Korea Institute of
Science and Technology Information, Daejeon 34141, South Korea  J. H. Yin
Korea University, Seoul 02841, South Korea  M. Yonenaga  Tokyo Metropolitan
University, Tokyo 192-0397, Japan  Y. M. Yook  Institute of High Energy
Physics, Chinese Academy of Sciences, Beijing 100049, China  T. Yoshinobu
Niigata University, Niigata 950-2181, Japan  C. Z. Yuan  Institute of High
Energy Physics, Chinese Academy of Sciences, Beijing 100049, China  G. Yuan
University of Science and Technology of China, Hefei 230026, China  W. Yuan
INFN Sezione di Padova, I-35131 Padova, Italy  Y. Yusa  Niigata University,
Niigata 950-2181, Japan  L. Zani  Centre de Physique des Particules de
Marseille, 13288 Marseille, France  J. Z. Zhang  Institute of High Energy
Physics, Chinese Academy of Sciences, Beijing 100049, China  Y. Zhang
University of Science and Technology of China, Hefei 230026, China  Z. Zhang
University of Science and Technology of China, Hefei 230026, China  V. Zhilich
Budker Institute of Nuclear Physics SB RAS, Novosibirsk 630090, Russian
Federation  Novosibirsk State University, Novosibirsk 630090, Russian
Federation  Q. D. Zhou  Graduate School of Science, Nagoya University, Nagoya
464-8602, Japan  X. Y. Zhou  Beihang University, Beijing 100191, China  V. I.
Zhukova  P.N. Lebedev Physical Institute of the Russian Academy of Sciences,
Moscow 119991, Russian Federation  V. Zhulanov  Budker Institute of Nuclear
Physics SB RAS, Novosibirsk 630090, Russian Federation  Novosibirsk State
University, Novosibirsk 630090, Russian Federation  A. Zupanc  J. Stefan
Institute, 1000 Ljubljana, Slovenia  The Belle II Collaboration

###### Abstract

This document presents the measurement of $B^{0}$ meson lifetimes using the
2019 Belle II dataset that corresponds to an integrated luminosity of $8.7\pm
0.2$ $\mbox{\,fb}^{-1}$. Each candidate is fully reconstructed with hadronic
decay final states on the signal side, while the rest-of-event technique
allows to infer the decay vertex position on the other (tag) side. $B^{0}$
lifetime is extracted from an unbinned maximum likelihood fit to the
distribution of the difference between the signal side $B^{0}$ candidate and
the tag side decay times. The measured lifetime is $\tau_{B^{0}}=1.48\pm
0.28\pm 0.06$ ps, where the first uncertainty is statistical and the second is
systematic.

Belle II, lifetime, time resolution

##  I Introduction

This document summarizes the $B^{0}$ lifetime measurement from hadronic decays
using the Belle II experiment early dataset. The analysis demonstrates the use
of vertex fitting tools and time resolution modeling. We describe the data
sets used, the selection of signal candidates and the fit strategy to extract
the lifetime parameter $\tau_{B^{0}}$. Finally, we present the results along
with an evaluation of the systematic uncertainties.

##  II Belle II detector and data sets used

The Belle II detector Abe  _et al._ (2010); Altmannshofer  _et al._ (2019a)
operates at the SuperKEKB asymmetric-energy electron-positron collider Akai
_et al._ (2018), located at the KEK laboratory in Tsukuba, Japan. The detector
consists of several subdetectors arranged around the beam pipe in a
cylindrical geometry. The innermost subdetector is the vertex detector (VXD),
which includes two layers of silicon pixel detectors Luetticke (2017) and four
outer layers of silicon strip detectors Adamczyk  _et al._ (2016). Currently,
the second pixel layer is installed in only a small part of the solid angle,
and the remaining VXD layers are fully installed. Most of the tracking volume
is consists of a helium-based, small-cell central drift chamber (CDC). Outside
the CDC, a Cherenkov-light angle and time-of-propagation detector (TOP)
provides charged-particle identification in the barrel region. In the forward
endcap, this function is provided by a proximity-focusing, aerogel ring
imaging Cherenkov detector (ARICH). An electromagnetic calorimeter (ECL)
consists of a barrel and two endcap sections made of CsI(Tl) crystals. A
uniform 1.5 T magnetic field is provided by a solenoid situated outside the
ECL. Multiple layers of scintillators and resistive plate chambers, inserted
between the magnetic flux-return iron plates, constitute the $K_{L}$ and muon
(KLM) identification system.

The data used in this analysis were collected at a center-of-mass energy of
10.58 GeV, corresponding to the mass of the $\mathchar 28935\relax{(4S)}$
resonance. The energies of the electron and positron beams are 7 GeV and 4
GeV, respectively, resulting in a boost of $\beta\gamma=0.28$ of the
$\mathchar 28935\relax{(4S)}$ relative to the lab frame. The integrated
luminosity used in this analysis is $8.7\pm 0.2$ $\mbox{\,fb}^{-1}$ Abudinén
_et al._ (2020).

We use also a generic simulated Monte Carlo (MC) sample that includes
$e^{+}e^{-}$ $\rightarrow$ $B^{0}{\kern-1.60004pt\kern
1.79993pt\overline{\kern-1.79993ptB}{}^{0}}$, $B^{+}{\kern-1.60004ptB^{-}}$,
$u\overline{u}$, $d\overline{d}$, $c\overline{c}$, $s\overline{s}$, and
$\tau^{+}\tau^{-}$ processes in adequate proportions and also beam background.
This sample corresponds to an integrated luminosity of $100$
$\mbox{\,fb}^{-1}$. All data and simulated samples are analysed with the Belle
II software Kuhr  _et al._ (2019).

##  III Event selection

Decay | Selection Criteria
---|---
$B^{0}$ decays
$B^{0}\rightarrow D^{-}\pi^{+}$ | $M_{bc}>5.2\>{\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ and $-0.2<\Delta E<0.2\>\mathrm{\,Ge\kern-1.00006ptV}$
$B^{0}\rightarrow D^{-}\rho^{+}$
$B^{0}\rightarrow D^{*-}\pi^{+}$
$B^{0}\rightarrow D^{*-}\rho^{+}$
$D$ decays
$D^{*+}\rightarrow D^{0}\pi^{-}$ | $0.143<m_{D^{*+}}-m_{D^{0}}<0.147\>{\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$
$D^{-}\rightarrow K^{+}\pi^{-}\pi^{-}$ | $|m-m_{PDG}|<0.015\>{\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$
$D^{0}\rightarrow K^{-}\pi^{+}$ | $|m-m_{PDG}|<0.015\>{\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$
$D^{0}\rightarrow K^{-}\pi^{+}\pi^{0}$
$D^{0}\rightarrow K^{-}\pi^{+}\pi^{+}\pi^{-}$
$\rho$ decay
$\rho^{+}\rightarrow\pi^{+}\pi^{0}$ | $|m-m_{PDG}|<0.10\>{\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$
Table 1: List of hadronic final states used to reconstruct $B$-meson decays.

The _signal side_ $B^{0}$ meson candidates are reconstructed as detailed in
Table 1, where $M_{bc}$ refers to the beam-energy-constrained mass, $\Delta E$
to the beam-energy difference Altmannshofer  _et al._ (2019b), $m$ is the
invariant mass of a particle and $m_{PDG}$ is its known mass. Charge
conjugation is implied throughout this document. The vertex position of the
_tag side_ $B$, the other $B$ daughter of the $\mathchar 28935\relax{(4S)}$
decay, is determined from the tracks not used to reconstruct the signal
candidate; the number of such tracks is required to be two or greater.

Pions and kaons are identified as follows:

  * •

The distance from the charged particle track to the interaction point in the
$r-\phi$ plane transverse to the beam is required to be less than 0.50 cm, and
the track’s $z$ position from the interaction point is less than 3.0 cm. A
selection based on particle identification likelihoods is used to identify
$\pi^{\pm}$ and $K^{\pm}$.

  * •

Charged pions coming from the $\rho^{\pm}$ or directly from the $B^{0}$ meson
have an additional requirement: the momentum in the $\mathchar
28935\relax{(4S)}$ center-of-mass frame of the mother particle must be larger
than $0.20\>{\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$.

  * •

$\pi^{0}$ candidates are formed from pairs of photons, with each photon having
an energy greater than 30 MeV, 80 MeV, or 120 MeV if reconstructed in the
barrel region, backward end-cap region, or forward end-cap region,
respectively. The angle difference between the momenta of the two photons is
required to be less than $0.90$ radians and less than $1$ radian for the angle
in the $r-\phi$ plane. The $\pi^{0}$ mass is required to be between $121$ and
$142$ ${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$; subsequently, a mass
constrained fit is then performed and only candidates surviving the fit pass
through the selection.

Suppression of continuum background ($e^{+}e^{-}$ $\rightarrow$
$u\overline{u}$, $d\overline{d}$, $s\overline{s}$, $c\overline{c}$) is
achieved by requiring the following:

  * •

Reduced Fox-Wolfram moment $R_{2}<$ 0.3 Altmannshofer  _et al._ (2019b),

  * •

Cosine of angle between the thrust axis Altmannshofer  _et al._ (2019b) of the
signal $B^{0}$ and the thrust axis of rest of event
$\cos{\theta_{\rm{thrust}}}<0.8$.

The fitted region, signal region, and sideband region are defined as follows:

  * •

Fit region $M_{bc}\in[5.20,5.29]\,\mathrm{\,Ge\kern-1.00006ptV}/c^{2}$ and
$\Delta E\in[-0.20,0.15]\,\mathrm{\,Ge\kern-1.00006ptV}$

  * •

Signal region: $M_{bc}\in[5.27,5.29]\,\mathrm{\,Ge\kern-1.00006ptV}/c^{2}$ and
$\Delta E\in[-0.07,0.05]\,\mathrm{\,Ge\kern-1.00006ptV}$

  * •

Sideband region: $M_{bc}\in[5.20,5.26]\,\mathrm{\,Ge\kern-1.00006ptV}/c^{2}$
and $\Delta E\in[-0.20,-0.10]\cup[0.10,1.50]\,\mathrm{\,Ge\kern-1.00006ptV}$
and $R_{2}>0.4$ and $\cos{\theta_{\rm{thrust}}}<0.8$

The fraction of events with multiple candidates in the signal region used for
the final fit to extract $B^{0}$ lifetime is 5%. No best candidate selection
is required and all candidates are kept.

The fit to the signal and tag side vertices is performed as follows. The
_signal side_ vertex is reconstructed from the hadronic decays listed in Table
1 using a kinematic fit of the whole signal decay chain Krohn  _et al._
(2019). The _tag side_ vertex position is determined from the tracks not used
to reconstruct the signal side with an adaptive vertex fitter that accounts
for the bias due to secondary decays Waltenberger (2011).

##  IV Time difference between the two $B$ mesons

The proper time difference $\Delta t=t_{\rm sgn}-t_{\rm tag}$ between the two
$B$ meson candidates (signal and tag) is approximated from the distance
$\Delta z_{boost}$ between the two reconstructed vertices along the collision
boost direction $\vec{\beta}$ as follows;

$\Delta t=\frac{\Delta z_{\rm{boost}}}{\beta\gamma\,c}.$ (1)

For each event, the uncertainty $\sigma_{\Delta t}$ on the calculated $\Delta
t$ is computed. Candidates are required to pass two additional cuts:

  * •

$|\Delta t|<8{\rm\,ps}$,

  * •

$\sigma_{\Delta t}<3.5{\rm\,ps}$.

##  V Fit strategy

In order to estimate the $B^{0}$ lifetime from the selected candidates, an
unbinned maximum likelihood fit is performed on the overall $\Delta t$
distribution. The $\Delta t$ function used in the fit is the sum of three
components,

$\displaystyle\mathrm{\textit{P}}_{\rm all}(\Delta t)=n_{\rm
sgn}\>\mathrm{\textit{P}}_{\rm sgn}(\Delta t,\tau_{B^{0}})+n_{\rm
b\overline{b}}\>\mathrm{\textit{P}}_{\rm b\overline{b}}(\Delta
t,\tau_{\textrm{eff}})+n_{\rm cont}\>\mathrm{\textit{P}}_{\rm cont}(\Delta
t),$ (2)

where $n_{\rm sgn},n_{\rm b\overline{b}}$, and $n_{\rm cont}$ are the yields,
respectively, of signal events ($B^{0}$ decaying in one of the hadronic decays
listed in Table 1 and correctly reconstruced), $b\overline{b}$ events
($B^{0}{\kern-1.60004pt\kern 1.79993pt\overline{\kern-1.79993ptB}{}^{0}}$ or
$B^{+}{\kern-1.60004ptB^{-}}$ wrongly reconstructed as signal decays) and
continuum events $(u\bar{u},c\bar{c},d\bar{d},s\bar{s}$ wrongly reconstructed
as signal decays). $\>\mathrm{\textit{P}}_{\rm sgn},\>\mathrm{\textit{P}}_{\rm
b\overline{b}},\>\mathrm{\textit{P}}_{\rm cont}$ are consequently the signal,
$b\overline{b}$, and continuum probability density functions, respectively,
used in the unbinned likelihood fit.

An important ingredient of the fit to extract the $B^{0}$ lifetime
$\tau_{B^{0}}$ is the resolution function ${\cal R}$ that describes the
smearing impacting the $\Delta t$ measurement due to various experimental
effects. In this analysis ${\cal R}$ is modeled by the sum of three Gaussian
distributions:

$\displaystyle\begin{aligned} \mathrm{{\cal R}}(\delta_{\Delta
t})=f_{1}\>{\cal{G}}(\delta_{\Delta
t};\mu_{1},\sigma_{1})+f_{2}\>{\cal{G}}(\delta_{\Delta
t};\mu_{1}+\Delta\mu,s_{2}\times\sigma_{1})\\\
+(1-f_{1}-f_{2})\>{\cal{G}}(\delta_{\Delta t};\mu_{1},s_{2}\times
s_{3}\times\sigma_{1}),\end{aligned}$ (3)

where $\>{\cal{G}}(x;\mu,\sigma)$ denotes a Gaussian distribution with mean
$\mu$ and width $\sigma$ and $\delta_{\Delta t}$ is the difference between the
reconstructed and the generated $\Delta t$.

${\cal R}$ is also used to describe the $z$-vertex residual, the distribution
of the difference between reconstructed and generated signal or tag vertex $z$
position, shown in Figure 4. The weighted sigma obtained from this latter fits
is $\sim 30\,\mu$m for the _signal side_ $B$ and $\sim 80\,\mu$m for the _tag
side_ $B$. These values correspond to an expected $\Delta t$ resolution of
$\sim 1$ ps. The bias toward positive values observed for the residual on the
tag side is due to the contribution from secondary decays.

The different contributions to Equation (2) are obtained from three separate
fits as follows.

  * $\bullet$ Fit 1

$n_{\rm sgn},n_{\rm b\overline{b}}$, and $n_{\rm cont}$ are obtained from a
two-dimensional extended maximum likelihood fit to the unbinned
$M_{bc}$–$\Delta E$ distributions (Figure 1). The yields in the signal region
are obtained with an integral of the probability density functions in the
signal region.

  * $\bullet$ Fit 2

$\mathrm{\textit{P}}_{\rm cont}(\Delta t)$ is the sum of three Gaussian
distributions having the same functional form as $\cal R$; this assumes no
lifetime for the continuum component. In the final fit to extract the $B^{0}$
lifetime, its shape is fixed using the parameters obtained from the fits to
the data side-band $\Delta t$ distributions shown in Figure 2, from simulated
and data samples.

  * $\bullet$ Fit 3

$\mathrm{\textit{P}}_{\rm b\overline{b}}(\Delta t,\tau_{\textrm{eff}})$ and
$\mathrm{\textit{P}}_{\rm sgn}(\Delta t,\tau_{B^{0}})$ are both modeled as an
exponential function convolved with the resolution model $\cal R$ described in
equation 3. The $b\overline{b}$ effective lifetime ($\tau_{\textrm{eff}}$) is
fixed from a separate fit to only the simulated $b\overline{b}$ contribution.
$\cal R$ is shared between $\mathrm{\textit{P}}_{\rm b\overline{b}}(\Delta
t,\tau_{\textrm{eff}})$ and $\mathrm{\textit{P}}_{\rm sgn}(\Delta
t,\tau_{B^{0}})$ in the $B^{0}$ lifetime fit. Its parameters, except
$\mu_{1res}$ and $\sigma_{1res}$, are fixed from a fit to the $\Delta t$
signal residuals obtained with the simulated sample and shown in Figure 3.

The final fit using Equation (2) to extract the $B^{0}$ lifetime from the
$\Delta t$ distribution of all the selected candidates is shown in Figure 5.
In this fit, only three parameters are left floating:
$\mu_{1res},\sigma_{1res}$ and $\tau_{B^{0}}$. The obtained lifetime is
$\tau_{B^{0}}$ = $1.48\pm 0.28$ ps and the corresponding reduced $\chi^{2}$
for this fit is 0.83. Table 2 enumerates the values of the parameters obtained
from fits to the simulated sample and that are fixed in the final fit extract
the $B^{0}$ lifetime on data. All parameters extracted from fits to the data
are summarized in Table 3. To avoid experimenters’ bias, the fit to the
$\Delta t$ distribution on data was performed after the analysis procedure was
finalized using simulated samples.

Figure 1: Projections of the $M_{bc}$–$\Delta E$ fit to the data sample to
extract the yields of the different components, see Table 3: (left) $M_{bc}$,
(right) $\Delta E$. The yellow, dark blue, and red lines present the fit
contributions corresponding to continuum, $b\overline{b}$, and signal
components, respectively. The sum of all fit components is presented in light
blue. The distributions refer to all $B^{0}\rightarrow D^{(*)}h$ decay
candidates selected as described in Section III.

Figure 2: Fit to the $\Delta t$ distribution of the sideband events in (left)
simulation and (right) data. The shape extracted from these fits, with
parameters listed in Tables 2 and 3, is used to describe the $\Delta t$
distribution of the continuum component. The distributions refer to all
$B^{0}\rightarrow D^{(*)}h$ decay candidates selected as described in Section
III. Figure 3: Fit to the $\Delta t$ residual for the signal contribution of
the simulated sample leaving all the parameters free. These parameters listed
in Table 2, except $\mu_{1_{res}}$and $\sigma_{1_{res}}$, are fixed for $\cal
R$ in the $B^{0}$ lifetime fit. The distributions refer to the true simulated
$B^{0}\rightarrow D^{(*)}h$ decays reconstructed and selected as described in
Section III.

Figure 4: Fit to the $z$-vertex residual for (left) the signal $B$ and (right)
the tag $B$, as obtained from the simulated signal sample. The distributions
refer to the true simulated $B^{0}\rightarrow D^{(*)}h$ decays reconstructed
and selected as described in Section III.

Figure 5: Fit to $\Delta t$ distribution for all $B^{0}\rightarrow D^{(*)}h$ selected decay candidates in the 2019 Belle II data set (logarithmic scale on top and linear scale on bottom). The yellow, dark blue, and red lines present the fit contributions corresponding to continuum, $b\overline{b}$ and signal components, respectively. The sum of all fit components is presented in light blue. See Sections III and V for explanations on the selection and fit procedures, respectively. | Fit parameter | value
---|---|---
Fit 2 |  $\Delta\mu_{cont}$ [${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ ] | $-0.0846\pm 0.026$
$f_{1cont}$ | $0.468\pm 0.021$
$f_{2cont}$ | $0.357\pm 0.017$
$s_{2cont}$ | $2.88\pm 0.096$
$s_{3cont}$ | $3.02\pm 0.11$
Fit 3 |  $\Delta\mu_{res}$ [${\mathrm{\,Ge\kern-1.00006ptV\\!/}c^{2}}$ ] | $-0.360\pm 0.031$
$f_{1res}$ | $0.561\pm 0.016$
$f_{2res}$ | $0.336\pm 0.014$
$s_{2res}$ | $2.84\pm 0.079$
$s_{3res}$ | $2.99\pm 0.13$
$\tau_{\textrm{eff}}$ [ps] | $1.31\pm 0.03$
Table 2: Values of the parameters obtained from unbinned maximum likelihood fits to the simulated sample: Fit 2 on $\Delta t$ distribution for the side-band and Fit 3 on the $\Delta t$ distribution for the signal contribution. | Fit parameter | value
---|---|---
Fit 1 |  $n_{sgn}$ fit region | $\left(1.22\pm 0.04\right)\times 10^{3}$
$n_{b\overline{b}}$ fit region | $\left(1.29\pm 0.07\right)\times 10^{3}$
$n_{cont}$ fit region | $\left(1.14\pm 0.06\right)\times 10^{3}$
$n_{sgn}$ signal region | $\left(1.10\pm 0.04\right)\times 10^{3}$
$n_{b\overline{b}}$ signal region | $270\pm 32$
$n_{cont}$ signal region | $140\pm 21$
Fit 2 |  $\mu_{1cont}$ [ps] | $0.021\pm 0.021$
$\sigma_{1cont}$ [ps] | $0.429\pm 0.015$
Final fit |  $\mu_{1res}$ [ps] | $-0.03\pm 0.06$
$\sigma_{1res}$ [ps] | $0.56\pm 0.18$
$\tau_{B^{0}}$ [ps] | $1.48\pm 0.28$
Table 3: Parameters extracted from unbinned maximum likelihood fits to the
data: Fit 1 on $M_{bc}$–$\Delta E$ 2D distribution, Fit 2 on $\Delta t$
distribution for the side-band and the Final fit on the $\Delta t$
distribution in the signal region.

##  VI Systematic studies

The limited size of the early data set on which this measurement is based,
from Section II, yields a statistical uncertainty of about 20%, while the
$B^{0}$ lifetime is known with a 0.3% relative uncertainty. Consequently,
systematic studies focused on the two main expected uncertainty sources: the
parametrizations used in the fits described in Section V (partly fixed from
simulated data) and the vertices reconstruction (embedding potential alignment
and calibration effects).

The first study relies on the reproduction of the full fit strategy for data
described in Section V over ten thousand simulated data samples with sizes
equivalent to the recorded data sample. Those samples were obtained with the
bootstrapping technique from a fully simulated sample ten times larger. From
the distribution of the ten thousand fitted lifetimes, a systematic
uncertainty of $0.05$ ps is obtained. Moreover, the final fit is repeated
leaving also $\tau_{\textrm{eff}}$ free, resulting in a further systematic
uncertainty of $0.01$ ps due to the difference with respect to the nominal fit
of the $B^{0}$ lifetime.

In a second step, the complete analysis is reproduced on a subset of the real
data, which was processed with two different calibration and alignment
constants to mimic the effect of the residual misalignment and miscalibration.
A systematic uncertainty of $0.03$ ps is extracted from the difference between
the lifetime values obtained.

The overall systematic uncertainty is obtained as the quadratic sum of these
contributions and amount to $0.06$ ps or 4% relative uncertainty.

##  VII Conclusion

A first measurement of the $B^{0}$ lifetime was performed with the 2019 Belle
II data set, which amounts to an integrated luminosity of $8.7\pm 0.2$
$\mbox{\,fb}^{-1}$. The estimated lifetime is $\tau_{B^{0}}=1.48\pm 0.28\pm
0.06$ ps, where the first uncertainty is statistical and the second is
systematic. This value is compatible with the world average of $1.519\pm
0.004$ ps Tanabashi  _et al._ (2018).

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