EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH (CERN)

 CERN-PH-EP-2014-033 LHCb-PAPER-2014-002 March,13 2014

Study of beauty hadron decays into pairs of charm hadrons

The LHCb collaboration†††Authors are listed on the following pages.

First observations of the decays
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D_{(s)}^{-}$ are reported
using data corresponding to an integrated luminosity of 3$\mbox{\,fb}^{-1}$
collected at 7 and 8$\mathrm{\,Te\kern-1.00006ptV}$ center-of-mass energy in
proton-proton collisions with the LHCb detector. In addition, the most precise
measurement of the branching fraction $\mathcal{B}(B_{s}^{0}\rightarrow
D^{+}D^{-}_{s})$ is made and a search is performed for the decays
$B^{0}_{(s)}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-}$. The results
obtained are

$\displaystyle\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-})/\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})$
$\displaystyle=$ $\displaystyle 0.042\pm 0.003\mathrm{\,(stat)}\pm
0.003\mathrm{\,(syst)},$
$\displaystyle\left[\frac{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})}{\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow
D^{+}D^{-}_{s})}\right]\big{/}\left[\frac{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}\pi^{-})}{\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}\pi^{-})}\right]$
$\displaystyle=$ $\displaystyle 0.96\pm 0.02\mathrm{\,(stat)}\pm
0.06\mathrm{\,(syst)},$ $\displaystyle\mathcal{B}(B_{s}^{0}\rightarrow
D^{+}D^{-}_{s})/\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})$
$\displaystyle=$ $\displaystyle 0.038\pm 0.004\mathrm{\,(stat)}\pm
0.003\mathrm{\,(syst)},$ $\displaystyle\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})/\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})$
$\displaystyle<$ $\displaystyle 0.0022\;[95\%\;{\rm C.L.}],$
$\displaystyle\mathcal{B}(B^{0}_{s}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})/\mathcal{B}(B_{s}^{0}\rightarrow
D^{+}D^{-}_{s})$ $\displaystyle<$ $\displaystyle 0.30\;[95\%\;{\rm C.L.}].$

Measurement of the mass of the ${\it\Lambda}_{b}^{0}$ baryon relative to the
${\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0}$ meson gives
${M({\it\Lambda}_{b}^{0})-M({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0})=339.72\pm
0.24\mathrm{\,(stat)}\pm
0.18\mathrm{\,(syst)}}$${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$. This result
provides the most precise measurement of the mass of the
${\it\Lambda}_{b}^{0}$ baryon to date.

Submitted to Physical Review Letters.

© CERN on behalf of the LHCb collaboration, license CC-BY-3.0.

LHCb collaboration

R. Aaij41, A. Abba21,u, B. Adeva37, M. Adinolfi46, A. Affolder52, Z.
Ajaltouni5, J. Albrecht9, F. Alessio38, M. Alexander51, S. Ali41, G.
Alkhazov30, P. Alvarez Cartelle37, A.A. Alves Jr25,38, S. Amato2, S. Amerio22,
Y. Amhis7, L. An3, L. Anderlini17,g, J. Anderson40, R. Andreassen57, M.
Andreotti16,f, J.E. Andrews58, R.B. Appleby54, O. Aquines Gutierrez10, F.
Archilli38, A. Artamonov35, M. Artuso59, E. Aslanides6, G. Auriemma25,n, M.
Baalouch5, S. Bachmann11, J.J. Back48, A. Badalov36, V. Balagura31, W.
Baldini16, R.J. Barlow54, C. Barschel38, S. Barsuk7, W. Barter47, V.
Batozskaya28, Th. Bauer41, A. Bay39, J. Beddow51, F. Bedeschi23, I. Bediaga1,
S. Belogurov31, K. Belous35, I. Belyaev31, E. Ben-Haim8, G. Bencivenni18, S.
Benson50, J. Benton46, A. Berezhnoy32, R. Bernet40, M.-O. Bettler47, M. van
Beuzekom41, A. Bien11, S. Bifani45, T. Bird54, A. Bizzeti17,i, P.M.
Bjørnstad54, T. Blake48, F. Blanc39, J. Blouw10, S. Blusk59, V. Bocci25, A.
Bondar34, N. Bondar30,38, W. Bonivento15,38, S. Borghi54, A. Borgia59, M.
Borsato7, T.J.V. Bowcock52, E. Bowen40, C. Bozzi16, T. Brambach9, J. van den
Brand42, J. Bressieux39, D. Brett54, M. Britsch10, T. Britton59, N.H. Brook46,
H. Brown52, A. Bursche40, G. Busetto22,q, J. Buytaert38, S. Cadeddu15, R.
Calabrese16,f, O. Callot7, M. Calvi20,k, M. Calvo Gomez36,o, A. Camboni36, P.
Campana18,38, D. Campora Perez38, F. Caponio21,u, A. Carbone14,d, G.
Carboni24,l, R. Cardinale19,38,j, A. Cardini15, H. Carranza-Mejia50, L.
Carson50, K. Carvalho Akiba2, G. Casse52, L. Cassina20, L. Castillo Garcia38,
M. Cattaneo38, Ch. Cauet9, R. Cenci58, M. Charles8, Ph. Charpentier38, S.-F.
Cheung55, N. Chiapolini40, M. Chrzaszcz40,26, K. Ciba38, X. Cid Vidal38, G.
Ciezarek53, P.E.L. Clarke50, M. Clemencic38, H.V. Cliff47, J. Closier38, C.
Coca29, V. Coco38, J. Cogan6, E. Cogneras5, P. Collins38, A. Comerma-
Montells36, A. Contu15,38, A. Cook46, M. Coombes46, S. Coquereau8, G. Corti38,
M. Corvo16,f, I. Counts56, B. Couturier38, G.A. Cowan50, D.C. Craik48, M. Cruz
Torres60, A.R. Cukierman56, S. Cunliffe53, R. Currie50, C. D’Ambrosio38, J.
Dalseno46, P. David8, P.N.Y. David41, A. Davis57, K. De Bruyn41, S. De
Capua54, M. De Cian11, J.M. De Miranda1, L. De Paula2, W. De Silva57, P. De
Simone18, D. Decamp4, M. Deckenhoff9, L. Del Buono8, N. Déléage4, D.
Derkach55, O. Deschamps5, F. Dettori42, A. Di Canto38, H. Dijkstra38, S.
Donleavy52, F. Dordei11, M. Dorigo39, C. Dorothy56, A. Dosil Suárez37, D.
Dossett48, A. Dovbnya43, F. Dupertuis39, P. Durante38, R. Dzhelyadin35, A.
Dziurda26, A. Dzyuba30, S. Easo49, U. Egede53, V. Egorychev31, S. Eidelman34,
S. Eisenhardt50, U. Eitschberger9, R. Ekelhof9, L. Eklund51,38, I. El Rifai5,
Ch. Elsasser40, S. Esen11, T. Evans55, A. Falabella16,f, C. Färber11, C.
Farinelli41, S. Farry52, D. Ferguson50, V. Fernandez Albor37, F. Ferreira
Rodrigues1, M. Ferro-Luzzi38, S. Filippov33, M. Fiore16,f, M. Fiorini16,f, M.
Firlej27, C. Fitzpatrick38, T. Fiutowski27, M. Fontana10, F. Fontanelli19,j,
R. Forty38, O. Francisco2, M. Frank38, C. Frei38, M. Frosini17,38,g, J. Fu21,
E. Furfaro24,l, A. Gallas Torreira37, D. Galli14,d, S. Gambetta19,j, M.
Gandelman2, P. Gandini59, Y. Gao3, J. Garofoli59, J. Garra Tico47, L.
Garrido36, C. Gaspar38, R. Gauld55, L. Gavardi9, E. Gersabeck11, M.
Gersabeck54, T. Gershon48, Ph. Ghez4, A. Gianelle22, S. Giani’39, V. Gibson47,
L. Giubega29, V.V. Gligorov38, C. Göbel60, D. Golubkov31, A. Golutvin53,31,38,
A. Gomes1,a, H. Gordon38, C. Gotti20, M. Grabalosa Gándara5, R. Graciani
Diaz36, L.A. Granado Cardoso38, E. Graugés36, G. Graziani17, A. Grecu29, E.
Greening55, S. Gregson47, P. Griffith45, L. Grillo11, O. Grünberg62, B. Gui59,
E. Gushchin33, Yu. Guz35,38, T. Gys38, C. Hadjivasiliou59, G. Haefeli39, C.
Haen38, S.C. Haines47, S. Hall53, B. Hamilton58, T. Hampson46, X. Han11, S.
Hansmann-Menzemer11, N. Harnew55, S.T. Harnew46, J. Harrison54, T. Hartmann62,
J. He38, T. Head38, V. Heijne41, K. Hennessy52, P. Henrard5, L. Henry8, J.A.
Hernando Morata37, E. van Herwijnen38, M. Heß62, A. Hicheur1, D. Hill55, M.
Hoballah5, C. Hombach54, W. Hulsbergen41, P. Hunt55, N. Hussain55, D.
Hutchcroft52, D. Hynds51, M. Idzik27, P. Ilten56, R. Jacobsson38, A. Jaeger11,
J. Jalocha55, E. Jans41, P. Jaton39, A. Jawahery58, M. Jezabek26, F. Jing3, M.
John55, D. Johnson55, C.R. Jones47, C. Joram38, B. Jost38, N. Jurik59, M.
Kaballo9, S. Kandybei43, W. Kanso6, M. Karacson38, T.M. Karbach38, M.
Kelsey59, I.R. Kenyon45, T. Ketel42, B. Khanji20, C. Khurewathanakul39, S.
Klaver54, O. Kochebina7, M. Kolpin11, I. Komarov39, R.F. Koopman42, P.
Koppenburg41,38, M. Korolev32, A. Kozlinskiy41, L. Kravchuk33, K. Kreplin11,
M. Kreps48, G. Krocker11, P. Krokovny34, F. Kruse9, M. Kucharczyk20,26,38,k,
V. Kudryavtsev34, K. Kurek28, T. Kvaratskheliya31, V.N. La Thi39, D.
Lacarrere38, G. Lafferty54, A. Lai15, D. Lambert50, R.W. Lambert42, E.
Lanciotti38, G. Lanfranchi18, C. Langenbruch38, B. Langhans38, T. Latham48, C.
Lazzeroni45, R. Le Gac6, J. van Leerdam41, J.-P. Lees4, R. Lefèvre5, A.
Leflat32, J. Lefrançois7, S. Leo23, O. Leroy6, T. Lesiak26, B. Leverington11,
Y. Li3, M. Liles52, R. Lindner38, C. Linn38, F. Lionetto40, B. Liu15, G.
Liu38, S. Lohn38, I. Longstaff51, I. Longstaff51, J.H. Lopes2, N. Lopez-
March39, P. Lowdon40, H. Lu3, D. Lucchesi22,q, H. Luo50, A. Lupato22, E.
Luppi16,f, O. Lupton55, F. Machefert7, I.V. Machikhiliyan31, F. Maciuc29, O.
Maev30, S. Malde55, G. Manca15,e, G. Mancinelli6, M. Manzali16,f, J. Maratas5,
J.F. Marchand4, U. Marconi14, C. Marin Benito36, P. Marino23,s, R. Märki39, J.
Marks11, G. Martellotti25, A. Martens8, A. Martín Sánchez7, M. Martinelli41,
D. Martinez Santos42, F. Martinez Vidal64, D. Martins Tostes2, A.
Massafferri1, R. Matev38, Z. Mathe38, C. Matteuzzi20, A. Mazurov16,38,f, M.
McCann53, J. McCarthy45, A. McNab54, R. McNulty12, B. McSkelly52, B.
Meadows57,55, F. Meier9, M. Meissner11, M. Merk41, D.A. Milanes8, M.-N.
Minard4, J. Molina Rodriguez60, S. Monteil5, D. Moran54, M. Morandin22, P.
Morawski26, A. Mordà6, M.J. Morello23,s, J. Moron27, R. Mountain59, F.
Muheim50, K. Müller40, R. Muresan29, B. Muster39, P. Naik46, T. Nakada39, R.
Nandakumar49, I. Nasteva1, M. Needham50, N. Neri21, S. Neubert38, N.
Neufeld38, M. Neuner11, A.D. Nguyen39, T.D. Nguyen39, C. Nguyen-Mau39,p, M.
Nicol7, V. Niess5, R. Niet9, N. Nikitin32, T. Nikodem11, A. Novoselov35, A.
Oblakowska-Mucha27, V. Obraztsov35, S. Oggero41, S. Ogilvy51, O. Okhrimenko44,
R. Oldeman15,e, G. Onderwater65, M. Orlandea29, J.M. Otalora Goicochea2, P.
Owen53, A. Oyanguren64, B.K. Pal59, A. Palano13,c, F. Palombo21,t, M.
Palutan18, J. Panman38, A. Papanestis49,38, M. Pappagallo51, C. Parkes54, C.J.
Parkinson9, G. Passaleva17, G.D. Patel52, M. Patel53, C. Patrignani19,j, A.
Pazos Alvarez37, A. Pearce54, A. Pellegrino41, M. Pepe Altarelli38, S.
Perazzini14,d, E. Perez Trigo37, P. Perret5, M. Perrin-Terrin6, L.
Pescatore45, E. Pesen66, K. Petridis53, A. Petrolini19,j, E. Picatoste
Olloqui36, B. Pietrzyk4, T. Pilař48, D. Pinci25, A. Pistone19, S. Playfer50,
M. Plo Casasus37, F. Polci8, A. Poluektov48,34, E. Polycarpo2, A. Popov35, D.
Popov10, B. Popovici29, C. Potterat2, A. Powell55, J. Prisciandaro39, A.
Pritchard52, C. Prouve46, V. Pugatch44, A. Puig Navarro39, G. Punzi23,r, W.
Qian4, B. Rachwal26, J.H. Rademacker46, B. Rakotomiaramanana39, M. Rama18,
M.S. Rangel2, I. Raniuk43, N. Rauschmayr38, G. Raven42, S. Reichert54, M.M.
Reid48, A.C. dos Reis1, S. Ricciardi49, A. Richards53, K. Rinnert52, V. Rives
Molina36, D.A. Roa Romero5, P. Robbe7, A.B. Rodrigues1, E. Rodrigues54, P.
Rodriguez Perez54, S. Roiser38, V. Romanovsky35, A. Romero Vidal37, M.
Rotondo22, J. Rouvinet39, T. Ruf38, F. Ruffini23, H. Ruiz36, P. Ruiz Valls64,
G. Sabatino25,l, J.J. Saborido Silva37, N. Sagidova30, P. Sail51, B.
Saitta15,e, V. Salustino Guimaraes2, C. Sanchez Mayordomo64, B. Sanmartin
Sedes37, R. Santacesaria25, C. Santamarina Rios37, E. Santovetti24,l, M.
Sapunov6, A. Sarti18,m, C. Satriano25,n, A. Satta24, M. Savrie16,f, D.
Savrina31,32, M. Schiller42, H. Schindler38, M. Schlupp9, M. Schmelling10, B.
Schmidt38, O. Schneider39, A. Schopper38, M.-H. Schune7, R. Schwemmer38, B.
Sciascia18, A. Sciubba25, M. Seco37, A. Semennikov31, K. Senderowska27, I.
Sepp53, N. Serra40, J. Serrano6, L. Sestini22, P. Seyfert11, M. Shapkin35, I.
Shapoval16,43,f, Y. Shcheglov30, T. Shears52, L. Shekhtman34, V. Shevchenko63,
A. Shires9, R. Silva Coutinho48, G. Simi22, M. Sirendi47, N. Skidmore46, T.
Skwarnicki59, N.A. Smith52, E. Smith55,49, E. Smith53, J. Smith47, M. Smith54,
H. Snoek41, M.D. Sokoloff57, F.J.P. Soler51, F. Soomro39, D. Souza46, B. Souza
De Paula2, B. Spaan9, A. Sparkes50, F. Spinella23, P. Spradlin51, F. Stagni38,
S. Stahl11, O. Steinkamp40, O. Stenyakin35, S. Stevenson55, S. Stoica29, S.
Stone59, B. Storaci40, S. Stracka23,38, M. Straticiuc29, U. Straumann40, R.
Stroili22, V.K. Subbiah38, L. Sun57, W. Sutcliffe53, K. Swientek27, S.
Swientek9, V. Syropoulos42, M. Szczekowski28, P. Szczypka39,38, D. Szilard2,
T. Szumlak27, S. T’Jampens4, M. Teklishyn7, G. Tellarini16,f, E. Teodorescu29,
F. Teubert38, C. Thomas55, E. Thomas38, J. van Tilburg41, V. Tisserand4, M.
Tobin39, S. Tolk42, L. Tomassetti16,f, D. Tonelli38, S. Topp-Joergensen55, N.
Torr55, E. Tournefier4, S. Tourneur39, M.T. Tran39, M. Tresch40, A.
Tsaregorodtsev6, P. Tsopelas41, N. Tuning41, M. Ubeda Garcia38, A. Ukleja28,
A. Ustyuzhanin63, U. Uwer11, V. Vagnoni14, G. Valenti14, A. Vallier7, R.
Vazquez Gomez18, P. Vazquez Regueiro37, C. Vázquez Sierra37, S. Vecchi16, J.J.
Velthuis46, M. Veltri17,h, G. Veneziano39, M. Vesterinen11, B. Viaud7, D.
Vieira2, M. Vieites Diaz37, X. Vilasis-Cardona36,o, A. Vollhardt40, D.
Volyanskyy10, D. Voong46, A. Vorobyev30, V. Vorobyev34, C. Voß62, H. Voss10,
J.A. de Vries41, R. Waldi62, C. Wallace48, R. Wallace12, J. Walsh23, S.
Wandernoth11, J. Wang59, D.R. Ward47, N.K. Watson45, A.D. Webber54, D.
Websdale53, M. Whitehead48, J. Wicht38, D. Wiedner11, G. Wilkinson55, M.P.
Williams45, M. Williams56, F.F. Wilson49, J. Wimberley58, J. Wishahi9, W.
Wislicki28, M. Witek26, G. Wormser7, S.A. Wotton47, S. Wright47, S. Wu3, K.
Wyllie38, Y. Xie61, Z. Xing59, Z. Xu39, Z. Yang3, X. Yuan3, O. Yushchenko35,
M. Zangoli14, M. Zavertyaev10,b, F. Zhang3, L. Zhang59, W.C. Zhang12, Y.
Zhang3, A. Zhelezov11, A. Zhokhov31, L. Zhong3, A. Zvyagin38.

1Centro Brasileiro de Pesquisas Físicas (CBPF), Rio de Janeiro, Brazil
2Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil
3Center for High Energy Physics, Tsinghua University, Beijing, China
4LAPP, Université de Savoie, CNRS/IN2P3, Annecy-Le-Vieux, France
5Clermont Université, Université Blaise Pascal, CNRS/IN2P3, LPC, Clermont-
Ferrand, France
6CPPM, Aix-Marseille Université, CNRS/IN2P3, Marseille, France
7LAL, Université Paris-Sud, CNRS/IN2P3, Orsay, France
8LPNHE, Université Pierre et Marie Curie, Université Paris Diderot,
CNRS/IN2P3, Paris, France
9Fakultät Physik, Technische Universität Dortmund, Dortmund, Germany
10Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany
11Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg,
Germany
12School of Physics, University College Dublin, Dublin, Ireland
13Sezione INFN di Bari, Bari, Italy
14Sezione INFN di Bologna, Bologna, Italy
15Sezione INFN di Cagliari, Cagliari, Italy
16Sezione INFN di Ferrara, Ferrara, Italy
17Sezione INFN di Firenze, Firenze, Italy
18Laboratori Nazionali dell’INFN di Frascati, Frascati, Italy
19Sezione INFN di Genova, Genova, Italy
20Sezione INFN di Milano Bicocca, Milano, Italy
21Sezione INFN di Milano, Milano, Italy
22Sezione INFN di Padova, Padova, Italy
23Sezione INFN di Pisa, Pisa, Italy
24Sezione INFN di Roma Tor Vergata, Roma, Italy
25Sezione INFN di Roma La Sapienza, Roma, Italy
26Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of
Sciences, Kraków, Poland
27AGH - University of Science and Technology, Faculty of Physics and Applied
Computer Science, Kraków, Poland
28National Center for Nuclear Research (NCBJ), Warsaw, Poland
29Horia Hulubei National Institute of Physics and Nuclear Engineering,
Bucharest-Magurele, Romania
30Petersburg Nuclear Physics Institute (PNPI), Gatchina, Russia
31Institute of Theoretical and Experimental Physics (ITEP), Moscow, Russia
32Institute of Nuclear Physics, Moscow State University (SINP MSU), Moscow,
Russia
33Institute for Nuclear Research of the Russian Academy of Sciences (INR RAN),
Moscow, Russia
34Budker Institute of Nuclear Physics (SB RAS) and Novosibirsk State
University, Novosibirsk, Russia
35Institute for High Energy Physics (IHEP), Protvino, Russia
36Universitat de Barcelona, Barcelona, Spain
37Universidad de Santiago de Compostela, Santiago de Compostela, Spain
38European Organization for Nuclear Research (CERN), Geneva, Switzerland
39Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
40Physik-Institut, Universität Zürich, Zürich, Switzerland
41Nikhef National Institute for Subatomic Physics, Amsterdam, The Netherlands
42Nikhef National Institute for Subatomic Physics and VU University Amsterdam,
Amsterdam, The Netherlands
43NSC Kharkiv Institute of Physics and Technology (NSC KIPT), Kharkiv, Ukraine
44Institute for Nuclear Research of the National Academy of Sciences (KINR),
Kyiv, Ukraine
45University of Birmingham, Birmingham, United Kingdom
46H.H. Wills Physics Laboratory, University of Bristol, Bristol, United
Kingdom
47Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
48Department of Physics, University of Warwick, Coventry, United Kingdom
49STFC Rutherford Appleton Laboratory, Didcot, United Kingdom
50School of Physics and Astronomy, University of Edinburgh, Edinburgh, United
Kingdom
51School of Physics and Astronomy, University of Glasgow, Glasgow, United
Kingdom
52Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom
53Imperial College London, London, United Kingdom
54School of Physics and Astronomy, University of Manchester, Manchester,
United Kingdom
55Department of Physics, University of Oxford, Oxford, United Kingdom
56Massachusetts Institute of Technology, Cambridge, MA, United States
57University of Cincinnati, Cincinnati, OH, United States
58University of Maryland, College Park, MD, United States
59Syracuse University, Syracuse, NY, United States
60Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio), Rio de
Janeiro, Brazil, associated to 2
61Institute of Particle Physics, Central China Normal University, Wuhan,
Hubei, China, associated to 3
62Institut für Physik, Universität Rostock, Rostock, Germany, associated to 11
63National Research Centre Kurchatov Institute, Moscow, Russia, associated to
31
64Instituto de Fisica Corpuscular (IFIC), Universitat de Valencia-CSIC,
Valencia, Spain, associated to 36
65KVI - University of Groningen, Groningen, The Netherlands, associated to 41
66Celal Bayar University, Manisa, Turkey, associated to 38

aUniversidade Federal do Triângulo Mineiro (UFTM), Uberaba-MG, Brazil
bP.N. Lebedev Physical Institute, Russian Academy of Science (LPI RAS),
Moscow, Russia
cUniversità di Bari, Bari, Italy
dUniversità di Bologna, Bologna, Italy
eUniversità di Cagliari, Cagliari, Italy
fUniversità di Ferrara, Ferrara, Italy
gUniversità di Firenze, Firenze, Italy
hUniversità di Urbino, Urbino, Italy
iUniversità di Modena e Reggio Emilia, Modena, Italy
jUniversità di Genova, Genova, Italy
kUniversità di Milano Bicocca, Milano, Italy
lUniversità di Roma Tor Vergata, Roma, Italy
mUniversità di Roma La Sapienza, Roma, Italy
nUniversità della Basilicata, Potenza, Italy
oLIFAELS, La Salle, Universitat Ramon Llull, Barcelona, Spain
pHanoi University of Science, Hanoi, Viet Nam
qUniversità di Padova, Padova, Italy
rUniversità di Pisa, Pisa, Italy
sScuola Normale Superiore, Pisa, Italy
tUniversità degli Studi di Milano, Milano, Italy
uPolitecnico di Milano, Milano, Italy

Hadrons are systems of quarks bound by the strong interaction, described at
the fundamental level by quantum chromodynamics (QCD). Low-energy phenomena,
such as the binding of quarks and gluons within hadrons, lie in the
nonperturbative regime of QCD and are difficult to calculate. Much progress
has been made in recent years in the study of beauty mesons[1]; however, many
aspects of beauty baryons are still largely unknown. Many decays of beauty
mesons into pairs of charm hadrons have branching fractions at the percent
level [2]. Decays of beauty baryons into pairs of charm hadrons are expected
to be of comparable size, yet none have been observed to date. If such decays
do have sizable branching fractions, they could be used to study beauty-baryon
properties. For example, a comparison of beauty meson and baryon branching
fractions can be used to test factorization in these decays.

Many models and techniques have been developed that attempt to reproduce the
spectrum of the measured hadron masses, such as constituent quark models or
lattice QCD calculations [3]. Precise measurements of ground-state beauty-
baryon masses are required to permit precision tests of a variety of QCD
models [4, 5, 6, 7, 8, 9, 10]. The ${\it\Lambda}_{b}^{0}$ baryon mass is
particularly interesting in this context since several ground-state beauty-
baryon masses are measured relative to that of the ${\it\Lambda}_{b}^{0}$
[11].

This Letter reports the first observation of the decays
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ and
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}$ made using data
corresponding to an integrated luminosity of 1 and 2$\mbox{\,fb}^{-1}$
collected at 7 and 8$\mathrm{\,Te\kern-1.00006ptV}$ center-of-mass energy in
$pp$ collisions, respectively, with the LHCb detector. The former is used to
make the most precise measurement to date of the mass of the
${\it\Lambda}_{b}^{0}$ baryon. Improved measurements of the branching fraction
$\mathcal{B}(B_{s}^{0}\rightarrow D^{+}D^{-}_{s})$ and stringent upper limits
on
$\mathcal{B}(B^{0}_{(s)}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})$
are also reported. Charge conjugated decay modes are implied throughout this
Letter.

The LHCb detector [12] is a single-arm forward spectrometer covering the
pseudorapidity range $2<\eta<5$, designed for the study of particles
containing $b$ or $c$ quarks. The detector includes a high-precision tracking
system consisting of a silicon-strip vertex detector surrounding the $pp$
interaction region, a large-area silicon-strip detector located upstream of a
dipole magnet with a bending power of about $4{\rm\,Tm}$, and three stations
of silicon-strip detectors and straw drift tubes [13] placed downstream. The
combined tracking system provides a momentum measurement with relative
uncertainty that varies from 0.4% at 5${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$
to 0.6% at 100${\mathrm{\,Ge\kern-1.00006ptV\\!/}c}$, and impact parameter
resolution of 20${\,\upmu\rm m}$ for tracks with large transverse momentum
($p_{\rm T}$). Different types of charged hadrons are distinguished by
information from two ring-imaging Cherenkov detectors [14]. The hardware stage
of the trigger uses information from calorimeter and muon systems [15]. The
calorimeter system consists of scintillating-pad and preshower detectors, an
electromagnetic calorimeter and a hadronic calorimeter. The muon system is
composed of alternating layers of iron and multiwire proportional chambers
[16]. The software stage of the trigger, which applies a full event
reconstruction, uses a boosted decision tree (BDT) [17] to identify secondary
vertices consistent with the decay of a beauty hadron [18].

Samples of simulated events are used to determine the signal selection
efficiency, to model signal event distributions and to investigate possible
background contributions. In the simulation, $pp$ collisions are generated
using Pythia [19, *Sjostrand:2007gs] with a specific LHCb configuration [21].
Decays of hadronic particles are described by EvtGen [22], in which final
state radiation is generated using Photos [23]. The interaction of the
generated particles with the detector and its response are implemented using
the Geant4 toolkit [24, *Agostinelli:2002hh] as described in Ref. [26].

In this analysis, signal beauty-hadron candidates are formed by combining
charm-hadron candidate pairs reconstructed in the following decay modes:
$D^{+}\rightarrow K^{-}\pi^{+}\pi^{+}$, $D_{s}^{+}\rightarrow
K^{-}K^{+}\pi^{+}$ and ${\it\Lambda}_{c}^{+}\rightarrow pK^{-}\pi^{+}$. The
measured invariant mass of each charm-hadron candidate, the resolution on
which is about $6-8$${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$, is required to
be within 25${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$ of the nominal value
[2]. To improve the resolution of the beauty-hadron mass, the decay chain is
fit imposing kinematic and vertex constraints [27]; this includes constraining
the charm-hadron masses to their nominal values. To suppress contributions
from non-charm decays, the reconstructed charm-hadron decay vertex is required
to be downstream of and significantly displaced from the reconstructed beauty-
hadron decay vertex.

A BDT is used to select each type of charm-hadron candidate. These BDTs use
five variables for the charm hadron and 23 for each of its decay products. The
variables include kinematic quantities, track and vertex qualities, and
particle identification (PID) information. The signal and background samples
used to train the BDTs are obtained from large samples of ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}\pi^{-}$, ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}_{s}\rightarrow D^{+}_{s}\pi^{-}$
and ${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}\pi^{-}$ decays. These
data samples are also used to validate selection efficiencies obtained from
simulation. The signal distributions are background subtracted using weights
[28] obtained from fits to the beauty-hadron invariant mass distributions. The
background distributions are taken from the charm-hadron and high-mass beauty-
hadron sidebands in the same data samples. To obtain the BDT efficiency in a
given signal decay mode, the kinematical properties and correlations between
the two charm hadrons are taken from simulation. The BDT response
distributions are obtained from validation data samples of the decays used in
the BDT training, weighted to match the kinematics of the signal.

Due to the kinematic similarity of the decays $D^{+}\rightarrow
K^{-}\pi^{+}\pi^{+}$, $D_{s}^{+}\rightarrow K^{-}K^{+}\pi^{+}$ and
${\it\Lambda}_{c}^{+}\rightarrow pK^{-}\pi^{+}$, cross-feed may occur among
beauty-hadron decays into pairs of charm hadrons. For example, cross-feed
between $D^{+}$ and $D^{+}_{s}$ mesons occurs when a $K^{-}h^{+}\pi^{+}$
candidate is reconstructed in the $D^{+}$ mass region under the
$h^{+}=\pi^{+}$ hypothesis and the $D^{+}_{s}$ mass region under the
$h^{+}=K^{+}$ hypothesis. In such situations, an arbitration is performed: if
the ambiguous track ($h^{+}$) can be associated to an oppositely-charged track
to form a $\phi(1020)\rightarrow K^{+}K^{-}$ candidate, the kaon hypothesis is
taken resulting in a $D_{s}^{+}$ assignment to the charm-hadron candidate;
otherwise, stringent PID requirements are applied to $h^{+}$. The efficiency
of these arbitrations is obtained using simulated signal decays to model the
kinematical properties and $D^{*+}\rightarrow D^{0}\pi^{+}$ calibration data
for the PID efficiencies.

Signal yields are determined by performing unbinned extended likelihood fits
to the beauty-hadron invariant mass spectra observed in the data. The signal
distributions are modeled using a so-called Apollonios function, which is the
exponential of a hyperbola combined with a power-law low-mass tail [29]. The
peak position and resolution parameters are allowed to vary while fitting the
data, while the low-mass tail parameters are taken from simulation and fixed
in the fits. The measurements reported in this paper are not sensitive to the
specific choice of the signal model.

Four categories of background contributions are considered: partially
reconstructed decays of beauty hadrons where at least one final-state particle
is not reconstructed; decays into a single charm hadron and three light
hadrons; reflections where the cross-feed arbitration fails to remove a
misidentified particle; and combinatorial background. The only partially
reconstructed decays that contribute in the mass region studied are those
where a single pion or photon is not reconstructed; thus, only final states
comprised of $D^{*+}_{(s)}$ or ${\it\Sigma}_{c}^{+}$ and another charm hadron
are considered (e.g.,
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{*-}_{s}$). These
background contributions are modeled using kernel probability density
functions (PDFs) [30] obtained from simulation. Single-charm backgrounds are
studied using data that are reconstructed outside of a given charm-hadron mass
region and are found to be $\mathcal{O}(1\%)$ for decays containing a
$D_{s}^{-}$ (e.g., $\overline{\kern-1.99997ptB}{}^{0}\rightarrow
D^{+}K^{-}K^{+}\pi^{-}$) and negligible otherwise. The only non-negligible
reflection is found to be
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ decays
misidentified as ${\it\Lambda}_{c}^{+}D^{-}$ candidates. The shape is obtained
from simulation, while the normalization is fixed using simulation and the
aforementioned PID calibration sample to determine the fraction of
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ decays that are
not removed by the cross-feed criteria. Reflections of ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s}$ decays
misidentified as final states containing ${\it\Lambda}_{c}^{+}$ particles do
not have a peaking structure and, therefore, are absorbed into the
combinatorial backgrounds, which are modeled using exponential distributions.

Figure 1 shows the invariant mass spectra for the
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ and
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}$ candidates. The
signal yields obtained are $4633\pm 69$ and $262\pm 19$ for
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ and
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}$, respectively. This
is the first observation of each of these decays. The ratio of branching
fractions determined using the nominal $D_{s}^{-}$ [2] and $D^{-}$ [31] meson
branching fractions and the ratio of efficiencies is

$\frac{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-})}{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})}=0.042\pm
0.003\mathrm{\,(stat)}\pm 0.003\mathrm{\,(syst)}.$

The similarity of the final states and the shared parent particle result in
many cancelations of uncertainties in the determination of the ratio of
branching fractions. The remaining uncertainties include roughly equivalent
contributions from determining the efficiency-corrected yields and from the
ratio of charm-hadron branching fractions (see Table 1). The dominant
contribution to the uncertainty of the fit PDF is due to the low-mass
background contributions, which are varied in size and shape to determine the
effect on the signal yield. The efficiencies of the cross-feed and BDT
criteria are determined in a data-driven manner that produces small
uncertainties. The observed ratio is approximately the ratio of the relevant
quark-mixing factors and meson decay constants,
$|V_{cd}/V_{cs}|^{2}\times(f_{D}/f_{D_{s}})^{2}\approx 0.034$, as expected
assuming nonfactorizable effects are small.

Figure 1:  Invariant mass distributions for (left) ${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ and (right) ${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}$ candidates with the fits described in the text overlaid.  Table 1: Relative systematic uncertainties on branching fraction measurements (%). The production ratio $\sigma(B^{0}_{s})/\sigma({\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0})$ is taken from Ref. [32]. Numbers in brackets in the last column are for the $B^{0}_{s}$ decay mode.  Source | $\frac{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-})}{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})}$ | $\left[\frac{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})}{\mathcal{B}({\kern 1.39998pt}\overline{\kern-1.39998ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})}\right]\big{/}\left[\frac{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}\pi^{-})}{\mathcal{B}({\kern 1.39998pt}\overline{\kern-1.39998ptB}{}^{0}\rightarrow D^{+}\pi^{-})}\right]$ | $\frac{\mathcal{B}(B_{s}^{0}\rightarrow D^{+}D^{-}_{s})}{\mathcal{B}({\kern 1.39998pt}\overline{\kern-1.39998ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})}$ | $\frac{\mathcal{B}(B^{0}_{(s)}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})}{\mathcal{B}(B_{(s)}^{0}\rightarrow D^{+}D^{-}_{s})}$
---|---|---|---|---
Efficiency | 3.5 | 5.2 | 1.0 | 3.9 (5.0)
Fit model | 3.0 | 2.6 | 3.0 | $-$
$\mathcal{B}(D^{+}_{(s)},{\it\Lambda}_{c}^{+})$ | 5.2 | $-$ | $-$ | 8.8
$\sigma(B^{0}_{s})/\sigma({\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0})$ | $-$ | $-$ | 5.8 | $-$
Total | 6.9 | 5.8 | 6.6 | 9.6 (10.1)

The branching fraction of the decay
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ is determined
relative to that of the ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s}$ decay.
Using $D^{+}D_{s}^{-}$ BDT criteria, optimized to maximize the expected
${\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0}$ significance, $19\,395\pm
145$ ${\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow
D^{+}D^{-}_{s}$ decays are observed (see Fig. 2). The measurement of
$\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})/\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})$ is
complicated by the fact that the ratio of the ${\it\Lambda}_{b}^{0}$ and
${\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0}$ production cross
sections, $\sigma({\it\Lambda}_{b}^{0})/\sigma({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0})$, depends on the $p_{\rm T}$ of
the beauty hadrons[33]. Figure 3 shows the ratio of efficiency-corrected
yields,
$N({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})/N({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})$, as a
function of beauty-hadron $p_{\rm T}$. The ratio of branching-fraction ratios
is obtained using a fit with the shape of the $p_{\rm T}$ dependence measured
in
$\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}\pi^{-})/\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}\pi^{-})$ [34] and
found to be

$\left[\frac{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})}{\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow
D^{+}D^{-}_{s})}\right]\big{/}\left[\frac{\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}\pi^{-})}{\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow
D^{+}\pi^{-})}\right]=0.96\pm 0.02\mathrm{\,(stat)}\pm 0.06\mathrm{\,(syst)}.$

This result does not depend on the absolute ratio of production cross sections
or on any charm-hadron branching fractions. The systematic uncertainties on
this result are listed in Table 1. The uncertainty in the fit model is largely
due to the sizable single-charm contributions to these modes and due to
contributions from the fits described in Ref. [34]. The ratio
$N({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})/N({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})$ is
observed to be consistent in data collected at $\sqrt{s}=7$ and
8$\mathrm{\,Te\kern-1.00006ptV}$; thus, it is assumed that the production
fractions of the ${\it\Lambda}_{b}^{0}$ and ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}$ are the same for all data
analyzed and no systematic uncertainty is assigned. The ratio of branching
ratios is consistent with unity as expected assuming small nonfactorizable
effects.

Figure 2:  Invariant mass distributions for $D^{+}D_{s}^{-}$ candidates
selected using BDT criteria optimized for the (left) ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s}$ and
(right) $B_{s}^{0}\rightarrow D^{+}D^{-}_{s}$ decay modes with the fits
described in the text overlaid.

The kinematic similarity of the decay modes
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ and ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s}$ permits
a precision measurement of the mass difference of the ${\it\Lambda}_{b}^{0}$
and ${\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0}$ hadrons to be made.
The relatively small value of
$\left[M({\it\Lambda}_{b}^{0})-M({\it\Lambda}_{c}^{+})-M(D_{s}^{-})\right]-\left[M({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0})-M(D^{+})-M(D_{s}^{-})\right]$
means that the uncertainty due to momentum scale, the dominant uncertainty in
absolute mass measurements, mostly cancels; however, it is still important to
determine accurately the momenta of the final state particles. The momentum
scale calibration of the spectrometer, which accounts for imperfect knowledge
of the magnetic field and alignment, is discussed in detail in Refs. [11, 35].
The uncertainty on the calibrated momentum scale is estimated to be 0.03% by
comparing various particle masses measured at LHCb to their nominal values
[35].

The kinematic and vertex constraints used in the fits described previously
reduce the statistical uncertainty on $M({\it\Lambda}_{b}^{0})-M({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0})$ by improving the resolution.
These constraints also increase the systematic uncertainty by introducing a
dependence on the precision of the nominal charm-hadron masses. For this
reason, these constraints are not imposed in the mass measurement. The mass
difference obtained is

$M({\it\Lambda}_{b}^{0})-M({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0})=339.72\pm
0.24\mathrm{\,(stat)}\pm
0.18\mathrm{\,(syst)}{\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}.$

The dominant systematic uncertainty (see Table 2) arises due to a correlation
between the reconstructed beauty-hadron mass and charm-hadron flight distance.
The large difference in the ${\it\Lambda}_{c}^{+}$ and $D^{+}$ hadron
lifetimes[2] causes only a partial cancelation of the biases induced by the
charm-lifetime selection criteria. This effect is studied in simulation and a
0.16${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$ uncertainty is assigned. The
0.03% uncertainty in the momentum scale results in an uncertainty on the mass
difference of 0.08${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$. Many variations
in the fit model are considered and none produce a significant shift in the
mass difference. The systematic uncertainty in the mass difference due to the
uncertainty in the amount of detector material in which charged particles lose
energy is negligible [35]. Furthermore, the uncertainty on
$M({\it\Lambda}_{b}^{0})-M({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0})$ due to differences in beauty-
hadron production kinematics, as seen in Fig. 3, is also found to be
negligible.

Using the nominal value for $M({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0})$[2] gives
$M({\it\Lambda}_{b}^{0})=5619.30\pm
0.34$${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$, where the uncertainty
includes both statistical and systematic contributions. This is the most
precise result to date. The total uncertainty is dominated by statistics and
charm-hadron lifetime effects; thus, this result can be treated as being
uncorrelated with the previous LHCb result obtained using the
${\it\Lambda}_{b}^{0}\rightarrow J/\psi{\it\Lambda}^{0}$ decay [36]. A
weighted average of the LHCb results gives $M({\it\Lambda}_{b}^{0})=5619.36\pm
0.26$${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$. This value may then be used
to improve the precision of the ${\it\Xi}_{b}^{-}$ and ${\it\Omega}_{b}^{-}$
baryon masses using their mass differences with respect to the
${\it\Lambda}_{b}^{0}$ baryon as reported in Ref. [36].

Table 2:  Systematic uncertainties for $M({\it\Lambda}_{b}^{0})-M({\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0})$.  Description | Value (${\mathrm{\,Me\kern-1.00006ptV\\!/}c^{2}}$)
---|---
${\it\Lambda}_{c}^{+}-D^{+}$ lifetime difference | 0.16
Momentum scale | 0.08
Fit model | 0.02
Total | 0.18

Using BDT criteria optimized for maximizing the expected significance of
${B_{s}^{0}\rightarrow D^{+}D^{-}_{s}}$, $14\,608\pm 121$ ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}$ and $143\pm 14$ $B_{s}^{0}$
decays are observed (see Fig. 2), from which the ratio extracted is

$\frac{\mathcal{B}(B_{s}^{0}\rightarrow D^{+}D^{-}_{s})}{\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow
D^{+}D^{-}_{s})}=0.038\pm 0.004\mathrm{\,(stat)}\pm 0.003\mathrm{\,(syst)}.$

This yields the most precise measurement to date of
$\mathcal{B}(B_{s}^{0}\rightarrow D^{+}D^{-}_{s})$ and supersedes Ref. [37].
The systematic uncertainty is dominated by the contribution from beauty-hadron
production fractions since the two decay modes share the same final state. The
additional small efficiency uncertainty is due to the uncertainty on the
$B_{s}^{0}$ lifetime. The fit model uncertainty is largely due to the size of
the combinatorial background near the $B_{s}^{0}$ peak. The ratio of branching
fractions is approximately the ratio of quark-mixing factors as expected
assuming nonfactorizable effects are small.

Figure 3:  Efficiency-corrected yield ratio of
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s}$ to ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s}$ vs
$p_{\rm T}$. The points are located at the mean $p_{\rm T}$ value of the
${\it\Lambda}_{b}^{0}$ in each bin. The curve shows the data fit with the
shape of the $p_{\rm T}$ dependence measured in Ref. [34].

A search is also performed for the decay modes
$B^{0}_{(s)}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-}$. Regions
centered around the nominal beauty-meson masses with boundaries defined such
that each region contains 95% of the corresponding signal are determined using
simulation. The expected background contribution in each of these regions is
obtained from the charm-hadron mass sidebands. Applying this technique to the
${\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s}$
and ${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{(s)}$ decays
produces background estimates consistent with those obtained by fitting the
invariant mass spectra for those modes. No significant excess is observed in
either ${\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-}$ signal region. The limits
obtained using the method of Ref. [38] and the known $D_{s}^{-}$ [2], $D^{-}$
[31] and ${\it\Lambda}_{c}^{+}$ [39] hadron branching fractions are

$\displaystyle\frac{\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})}{\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})}$
$\displaystyle<$ $\displaystyle 0.0022\;[95\%\;{\rm C.L.}],$
$\displaystyle\frac{\mathcal{B}(B^{0}_{s}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})}{\mathcal{B}(B_{s}^{0}\rightarrow
D^{+}D^{-}_{s})}$ $\displaystyle<$ $\displaystyle 0.30\;[95\%\;{\rm C.L.}].$

For these results the lifetime of the light-mass $B^{0}_{s}$ eigenstate is
assumed as this produces the most conservative limits[1]. This is the best
limit to date for the ${\kern 1.99997pt}\overline{\kern-1.99997ptB}{}^{0}$
decay mode and the first limit for the $B_{s}^{0}$ decay mode.

In summary, first observations and relative branching fraction measurements
have been made for the decays
${\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{(s)}$. The most
precise measurement of the ${\it\Lambda}_{b}^{0}$ baryon mass has been made
via its mass difference relative to the ${\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}$ meson. The most precise
measurement of $\mathcal{B}(B_{s}^{0}\rightarrow D^{+}D^{-}_{s})$ has been
presented and the most stringent upper limits have been placed on
$\mathcal{B}(B^{0}_{(s)}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})$.
Using the PDG value $\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}D^{-}_{s})=(7.2\pm
0.8)\times 10^{-3}$ [2] and the LHCb result for
${\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}\pi^{-})}/{\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow D^{+}\pi^{-})}$ [34],
the absolute branching fractions obtained are

$\displaystyle\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-}_{s})$
$\displaystyle=$ $\displaystyle(1.1\pm 0.1)\times 10^{-2},$
$\displaystyle\mathcal{B}({\it\Lambda}_{b}^{0}\rightarrow{\it\Lambda}_{c}^{+}D^{-})$
$\displaystyle=$ $\displaystyle(4.7\pm 0.6)\times 10^{-4},$
$\displaystyle\mathcal{B}(B_{s}^{0}\rightarrow D^{+}D^{-}_{s})$
$\displaystyle=$ $\displaystyle(2.7\pm 0.5)\times 10^{-4},$
$\displaystyle\mathcal{B}({\kern
1.99997pt}\overline{\kern-1.99997ptB}{}^{0}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})$
$\displaystyle<$ $\displaystyle 1.6\times 10^{-5}\,[95\%\,{\rm C.L.}],$
$\displaystyle\mathcal{B}(B^{0}_{s}\rightarrow{\it\Lambda}_{c}^{+}{\it\Lambda}_{c}^{-})$
$\displaystyle<$ $\displaystyle 8.0\times 10^{-5}\,[95\%\,{\rm C.L.}].$

These results are all consistent with expectations that assume small
nonfactorizable effects.

## Acknowledgements

We express our gratitude to our colleagues in the CERN accelerator departments
for the excellent performance of the LHC. We thank the technical and
administrative staff at the LHCb institutes. We acknowledge support from CERN
and from the national agencies: CAPES, CNPq, FAPERJ and FINEP (Brazil); NSFC
(China); CNRS/IN2P3 and Region Auvergne (France); BMBF, DFG, HGF and MPG
(Germany); SFI (Ireland); INFN (Italy); FOM and NWO (The Netherlands); SCSR
(Poland); MEN/IFA (Romania); MinES, Rosatom, RFBR and NRC “Kurchatov
Institute” (Russia); MinECo, XuntaGal and GENCAT (Spain); SNSF and SER
(Switzerland); NAS Ukraine (Ukraine); STFC (United Kingdom); NSF (USA). We
also acknowledge the support received from EPLANET and the ERC under FP7. The
Tier1 computing centres are supported by IN2P3 (France), KIT and BMBF
(Germany), INFN (Italy), NWO and SURF (The Netherlands), PIC (Spain), GridPP
(United Kingdom). We are indebted to the communities behind the multiple open
source software packages we depend on. We are also thankful for the computing
resources and the access to software R&D tools provided by Yandex LLC
(Russia).

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