16854 2107.09593 10.1007/JHEP10(2021)060 60 60 Observation of a Λ b 0 $$ {\varLambda}_b^0 $$ − Λ ¯ b 0 $$ {\overline{\varLambda}}_b^0 $$ production asymmetry in proton-proton collisions at s $$ \sqrt{s} $$ = 7 and 8 TeV Regular Article - Experimental Physics 1 38 2021 10 7 2021 7 21 2021 9 13 2021 9 14 2021 10 7 The Author(s) 2021 Open Access. This article is distributed under the terms of the Creative Commons Attribution License ( CC-BY 4.0 ), which permits any use, distribution and reproduction in any medium, provided the original author(s) and source are credited. 13130 2021 2021 10 10 The LHCb collaboration R. Aaij A. S. W. Abdelmotteleb C. Abellán Beteta T. Ackernley B. Adeva M. Adinolfi H. Afsharnia C. A. Aidala S. Aiola Z. Ajaltouni S. Akar J. Albrecht F. Alessio M. Alexander A. Alfonso Albero Z. Aliouche G. Alkhazov P. Alvarez Cartelle S. Amato J. L. Amey Y. Amhis L. An L. Anderlini A. Andreianov M. Andreotti F. Archilli A. Artamonov M. Artuso K. Arzymatov E. Aslanides M. 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Zunica grid.418228.5 0000 0004 0643 8134 Centro Brasileiro de Pesquisas Físicas (CBPF) Rio de Janeiro Brazil grid.8536.8 0000 0001 2294 473X Universidade Federal do Rio de Janeiro (UFRJ) Rio de Janeiro Brazil grid.12527.33 0000 0001 0662 3178 Center for High Energy Physics Tsinghua University Beijing China grid.418741.f 0000 0004 0632 3097 Institute Of High Energy Physics (IHEP) Beijing China grid.11135.37 0000 0001 2256 9319 School of Physics State Key Laboratory of Nuclear Physics and Technology Peking University Beijing China grid.410726.6 0000 0004 1797 8419 University of Chinese Academy of Sciences Beijing China grid.411407.7 0000 0004 1760 2614 Institute of Particle Physics Central China Normal University Wuhan Hubei China grid.5388.6 Univ. 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Wills Physics Laboratory University of Bristol Bristol United Kingdom grid.5335.0 0000000121885934 Cavendish Laboratory University of Cambridge Cambridge United Kingdom grid.7372.1 0000 0000 8809 1613 Department of Physics University of Warwick Coventry United Kingdom grid.76978.37 0000 0001 2296 6998 STFC Rutherford Appleton Laboratory Didcot United Kingdom grid.4305.2 0000 0004 1936 7988 School of Physics and Astronomy University of Edinburgh Edinburgh United Kingdom grid.8756.c 0000 0001 2193 314X School of Physics and Astronomy University of Glasgow Glasgow United Kingdom grid.10025.36 0000 0004 1936 8470 Oliver Lodge Laboratory University of Liverpool Liverpool United Kingdom grid.7445.2 0000 0001 2113 8111 Imperial College London London United Kingdom grid.5379.8 0000000121662407 Department of Physics and Astronomy University of Manchester Manchester United Kingdom grid.4991.5 0000 0004 1936 8948 Department of Physics University of Oxford Oxford United Kingdom grid.116068.8 0000 0001 2341 2786 Massachusetts Institute of Technology Cambridge MA United States grid.24827.3b 0000 0001 2179 9593 University of Cincinnati Cincinnati OH United States grid.164295.d 0000 0001 0941 7177 University of Maryland College Park MD United States grid.148313.c 0000 0004 0428 3079 Los Alamos National Laboratory (LANL) Los Alamos United States grid.264484.8 0000 0001 2189 1568 Syracuse University Syracuse NY United States grid.1002.3 0000 0004 1936 7857 School of Physics and Astronomy Monash University Melbourne Australia grid.4839.6 0000 0001 2323 852X Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio) Rio de Janeiro Brazil grid.67293.39 Physics and Micro Electronic College Hunan University Changsha City China grid.263785.d 0000 0004 0368 7397 Guangdong Provincial Key Laboratory of Nuclear Science, Guangdong-Hong Kong Joint Laboratory of Quantum Matter, Institute of Quantum Matter South China Normal University Guangzhou China grid.49470.3e 0000 0001 2331 6153 School of Physics and Technology Wuhan University Wuhan China grid.10689.36 0000 0001 0286 3748 Departamento de Fisica Universidad Nacional de Colombia Bogota Colombia grid.10388.32 0000 0001 2240 3300 Universität Bonn — Helmholtz-Institut für Strahlen und Kernphysik Bonn Germany grid.10493.3f 0000000121858338 Institut für Physik Universität Rostock Rostock Germany grid.5591.8 0000 0001 2294 6276 Eotvos Lorand University Budapest Hungary grid.470215.5 INFN Sezione di Perugia Perugia Italy grid.4830.f 0000 0004 0407 1981 Van Swinderen Institute University of Groningen Groningen Netherlands grid.5012.6 0000 0001 0481 6099 Universiteit Maastricht Maastricht Netherlands grid.18919.38 0000000406204151 National Research Centre Kurchatov Institute Moscow Russia grid.410682.9 0000 0004 0578 2005 National Research University Higher School of Economics Moscow Russia grid.35043.31 0000 0001 0010 3972 National University of Science and Technology “MISIS” Moscow Russia grid.27736.37 0000 0000 9321 1499 National Research Tomsk Polytechnic University Tomsk Russia grid.6162.3 0000 0001 2174 6723 DS4DS, La Salle Universitat Ramon Llull Barcelona Spain grid.214458.e 0000000086837370 University of Michigan Ann Arbor United States grid.411281.f 0000 0004 0643 8003 Universidade Federal do Triângulo Mineiro (UFTM) Uberaba MG Brazil grid.410726.6 0000 0004 1797 8419 Hangzhou Institute for Advanced Study UCAS Hangzhou China grid.7644.1 0000 0001 0120 3326 Università di Bari Bari Italy grid.6292.f 0000 0004 1757 1758 Università di Bologna Bologna Italy grid.7763.5 0000 0004 1755 3242 Università di Cagliari Cagliari Italy grid.8484.0 0000 0004 1757 2064 Università di Ferrara Ferrara Italy grid.8404.8 0000 0004 1757 2304 Università di Firenze Firenze Italy grid.5606.5 0000 0001 2151 3065 Università di Genova Genova Italy grid.4708.b 0000 0004 1757 2822 Università degli Studi di Milano Milano Italy grid.7563.7 0000 0001 2174 1754 Università di Milano Bicocca Milano Italy grid.7548.e 0000000121697570 Università di Modena e Reggio Emilia Modena Italy grid.5608.b 0000 0004 1757 3470 Università di Padova Padova Italy grid.6093.c Scuola Normale Superiore Pisa Italy grid.5395.a 0000 0004 1757 3729 Università di Pisa Pisa Italy grid.7367.5 0000000119391302 Università della Basilicata Potenza Italy grid.6530.0 0000 0001 2300 0941 Università di Roma Tor Vergata Roma Italy grid.9024.f 0000 0004 1757 4641 Università di Siena Siena Italy grid.12711.34 0000 0001 2369 7670 Università di Urbino Urbino Italy grid.449125.f 0000 0001 0170 9976 MSU — Iligan Institute of Technology (MSU-IIT) Iligan Philippines grid.9922.0 0000 0000 9174 1488 AGH — University of Science and Technology, Faculty of Computer Science, Electronics and Telecommunications Kraków Poland grid.4886.2 0000 0001 2192 9124 P.N. Lebedev Physical Institute Russian Academy of Science (LPI RAS) Moscow Russia grid.4605.7 0000000121896553 Novosibirsk State University Novosibirsk Russia grid.8993.b 0000 0004 1936 9457 Department of Physics and Astronomy Uppsala University Uppsala Sweden grid.493130.c Hanoi University of Science Hanoi Vietnam Abstract This article presents differential measurements of the asymmetry between Λ b 0 $$ {\varLambda}_b^0 $$ and Λ ¯ b 0 $$ {\overline{\varLambda}}_b^0 $$ baryon production rates in proton-proton collisions at centre-of-mass energies of s $$ \sqrt{s} $$ = 7 and 8 TeV collected with the LHCb experiment, corresponding to an integrated luminosity of 3 fb −1. The Λ b 0 $$ {\varLambda}_b^0 $$ baryons are reconstructed through the inclusive semileptonic decay Λ b 0 $$ {\varLambda}_b^0 $$ → Λ c + $$ {\varLambda}_c^{+} $$ μ − ν ¯ $$ \overline{\nu} $$ μ X. The production asymmetry is measured both in intervals of rapidity in the range 2.15 < y < 4.10 and transverse momentum in 2 < p T < 27 GeV/c. The results are found to be incompatible with symmetric production with a significance of 5.8 standard deviations for both s $$ \sqrt{s} $$ = 7 and 8 TeV data, assuming no CP violation in the decay. There is evidence for a trend as a function of rapidity with a significance of 4 standard deviations. Comparisons to predictions from hadronisation models in Pythia and heavy-quark recombination are provided. This result constitutes the first observation of a particle-antiparticle asymmetry in b-hadron production at LHC energies.

Keywords Hadron-Hadron scattering (experiments) Heavy quark production proton-proton scattering Hard scattering B physics ArXiv ePrint: 2107.09593 U. Egede and T. Hadavizadeh are associated to Department of Physics, University of Warwick, Coventry, United Kingdom C. Göbel is associated to Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil L. Dai, J. Yu and S. Zhang are associated to Institute of Particle Physics, Central China Normal University, Wuhan, Hubei, China A. Bursche, J. Hu, H. Li, G. Liu, L. Bian, H. Cai, B. Fang, X. Huang, L. Sun and J. Wang are associated to Center for High Energy Physics, Tsinghua University, Beijing, China D. A. Milanes, I. A. Monroy and J. A. Rodriguez Lopez are associated to LPNHE, Sorbonne Université, Paris Diderot Sorbonne Paris Cité, CNRS/IN2P3, Paris, France A. B. Morris, S. Neubert, M. Sarpis, N. Meinert and H. Viemann are associated to Physikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany B. Dey is associated to European Organization for Nuclear Research (CERN), Geneva, Switzerland V. Duk and M. Piccini are associated to INFN Sezione di Ferrara, Ferrara, Italy K. De Bruyn, C. J. G. Onderwater, M. van Veghel, J. A. de Vries, M. Merk, C. J. Pawley and K. Vos are associated to Nikhef National Institute for Subatomic Physics, Amsterdam, Netherlands A. Malinin, A. Petrov, V. Shevchenko, F. Baryshnikov, S. Dadabaev, S. Didenko, A. Golutvin, S. Gromov, A. Ishteev, A. Kondybayeva, O. Lantwin, S. Legotin, N. Polukhina, D. Saranin, I. Shchemerov, E. Shmanin, O. Steinkamp, D. Strekalina, A. Terentev, E. Trifonova, E. Ursov, E. van Herwijnen, A. Zharkova, A. Kharisova, G. Panshin and A. Vagner are associated to Institute of Theoretical and Experimental Physics NRC Kurchatov Institute (ITEP NRC KI), Moscow, Russia A. Boldyrev, D. Derkach, M. Hushchyn, M. Karpov, A. Maevskiy, F. Ratnikov, A. Ryzhikov and A. Ustyuzhanin are associated to Yandex School of Data Analysis, Moscow, Russia M. Calvo Gomez, E. Golobardes, N. Valls Canudas and X. Vilasis-Cardona are associated to ICCUB, Universitat de Barcelona, Barcelona, Spain C. A. Aidala, D. S. Fitzgerald, S. H. Lee, K. R. Mattioli, C. Nunez, J. D. Roth and D. M. Shangase are associated to Syracuse University, Syracuse, NY, United States