Evidence for the Rare Decay B+ → Λ  ̄ pμ+μ

(LHCb Collaboration)

doi:10.1103/pl88-4435

Evidence for the Rare Decay B+ → Λ ̄ pμ+μ

(LHCb Collaboration)

Science Park 105
University of Warwick
Physik-Institut der Universität Zürich
University of Liverpool
Syracuse University
Universidade de Santiago de Compostela
University of Bristol
SUPA
University of Glasgow
Department of Physics and Astronomy
Uppsala University
Université Paris-Saclay
University of Michigan, Ann Arbor
Clermont-Auvergne University
Faculty of Physics and Applied Computer Science
Agh University of Science and Technology Faculty of Computer Science
LNF-INFN
Fakultät Physik
University of Dortmund
Lamarr Institute for Machine Learning and Artificial Intelligence
Physikalisches Institut
University of Freiburg
Vilnius University
European Organization for Nuclear Research
University of Cambridge
Sorbonne Université
Instituto de Biofisica da UFRJ
State Key Laboratory of Nuclear Physics and Technology
Istituto Nazionale di Fisica Nucleare, Sezione di Firenze
Sezione INFN di Ferrara
Universidade da Coruña
INFN Sezione di Milano-Bicocca
University of Milano-Bicocca
University of Chinese Academy of Sciences
INFN Roma Tor Vergata
Consejo Nacional de Rectores (CONARE)
Aix-Marseille Université
Institute of Physics
ENAC-IIC-GEL
Massachusetts Institute of Technology
Ip Paris
University of Oxford

Research output: Contribution to journal › Article › peer-review

Abstract

A search for the rare decay B+→Λ¯pμ+μ- is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of s=13 TeV, corresponding to an integrated luminosity of 5.4 fb-1. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of m(Λ¯p)<2.8 GeV/c2. The branching fraction is measured to be Blow(B+→Λ¯pμ+μ-)=(1.70-0.56+0.65(stat)±0.17(syst)±0.14(ext))×10-8, where the last uncertainty is due to external inputs on B(B+→J/ψΛ¯p)×B(J/ψ→μ+μ-). With no significant signal observed in the high m(Λ¯p) region above 2.8 GeV/c2, an upper limit is set to be Bhigh(B+→Λ¯pμ+μ-)<2.8(3.7)×10-9 at the 90% (95%) confidence level.

Original language	English
Article number	051801
Journal	Physical Review Letters
Volume	137
Issue number	5
DOIs	https://doi.org/10.1103/pl88-4435
Publication status	Published - 31 Jul 2026

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10.1103/pl88-4435

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@article{1e3f5dc38470404ca923827053ccc5e8,

title = "Evidence for the Rare Decay B+ → Λ{\= } pμ+μ",

abstract = "A search for the rare decay B+→Λ¯pμ+μ- is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of s=13 TeV, corresponding to an integrated luminosity of 5.4 fb-1. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of m(Λ¯p)<2.8 GeV/c2. The branching fraction is measured to be Blow(B+→Λ¯pμ+μ-)=(1.70-0.56+0.65(stat)±0.17(syst)±0.14(ext)){\texttimes}10-8, where the last uncertainty is due to external inputs on B(B+→J/ψΛ¯p){\texttimes}B(J/ψ→μ+μ-). With no significant signal observed in the high m(Λ¯p) region above 2.8 GeV/c2, an upper limit is set to be Bhigh(B+→Λ¯pμ+μ-)<2.8(3.7){\texttimes}10-9 at the 90\% (95\%) confidence level.",

author = "\{(LHCb Collaboration)\} and R. Aaij and Abdelmotteleb, \{A. S.W.\} and \{Abellan Beteta\}, C. and F. Abudin{\'e}n and T. Ackernley and Adefisoye, \{A. A.\} and B. Adeva and M. Adinolfi and P. Adlarson and C. Agapopoulou and Aidala, \{C. A.\} and Z. Ajaltouni and S. Akar and K. Akiba and M. Akthar and P. Albicocco and J. Albrecht and R. Aleksiejunas and F. Alessio and \{Alvarez Cartelle\}, P. and R. Amalric and S. Amato and Amey, \{J. L.\} and Y. Amhis and L. An and L. Anderlini and M. Andersson and P. Andreola and M. Andreotti and \{Andres Estrada\}, S. and A. Anelli and D. Ao and C. Arata and F. Archilli and Z. Areg and M. Argenton and \{Arguedas Cuendis\}, S. and L. Arnone and A. Artamonov and M. Artuso and E. Aslanides and \{Ata{\'i}de Da Silva\}, R. and M. Atzeni and B. Audurier and Authier, \{J. A.\} and D. Bacher and V. Balagura and F. Fleuret and E. Maurice and Niel, \{E. M.\}",

note = "Publisher Copyright: {\textcopyright} 2026 CERN. ",

year = "2026",

month = jul,

day = "31",

doi = "10.1103/pl88-4435",

language = "English",

volume = "137",

journal = "Physical Review Letters",

issn = "0031-9007",

publisher = "American Physical Society",

number = "5",

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TY - JOUR

T1 - Evidence for the Rare Decay B+ → Λ ̄ pμ+μ

AU - (LHCb Collaboration)

AU - Aaij, R.

AU - Abdelmotteleb, A. S.W.

AU - Abellan Beteta, C.

AU - Abudinén, F.

AU - Ackernley, T.

AU - Adefisoye, A. A.

AU - Adeva, B.

AU - Adinolfi, M.

AU - Adlarson, P.

AU - Agapopoulou, C.

AU - Aidala, C. A.

AU - Ajaltouni, Z.

AU - Akar, S.

AU - Akiba, K.

AU - Akthar, M.

AU - Albicocco, P.

AU - Albrecht, J.

AU - Aleksiejunas, R.

AU - Alessio, F.

AU - Alvarez Cartelle, P.

AU - Amalric, R.

AU - Amato, S.

AU - Amey, J. L.

AU - Amhis, Y.

AU - An, L.

AU - Anderlini, L.

AU - Andersson, M.

AU - Andreola, P.

AU - Andreotti, M.

AU - Andres Estrada, S.

AU - Anelli, A.

AU - Ao, D.

AU - Arata, C.

AU - Archilli, F.

AU - Areg, Z.

AU - Argenton, M.

AU - Arguedas Cuendis, S.

AU - Arnone, L.

AU - Artamonov, A.

AU - Artuso, M.

AU - Aslanides, E.

AU - Ataíde Da Silva, R.

AU - Atzeni, M.

AU - Audurier, B.

AU - Authier, J. A.

AU - Bacher, D.

AU - Balagura, V.

AU - Fleuret, F.

AU - Maurice, E.

AU - Niel, E. M.

PY - 2026/7/31

Y1 - 2026/7/31

N2 - A search for the rare decay B+→Λ¯pμ+μ- is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of s=13 TeV, corresponding to an integrated luminosity of 5.4 fb-1. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of m(Λ¯p)<2.8 GeV/c2. The branching fraction is measured to be Blow(B+→Λ¯pμ+μ-)=(1.70-0.56+0.65(stat)±0.17(syst)±0.14(ext))×10-8, where the last uncertainty is due to external inputs on B(B+→J/ψΛ¯p)×B(J/ψ→μ+μ-). With no significant signal observed in the high m(Λ¯p) region above 2.8 GeV/c2, an upper limit is set to be Bhigh(B+→Λ¯pμ+μ-)<2.8(3.7)×10-9 at the 90% (95%) confidence level.

AB - A search for the rare decay B+→Λ¯pμ+μ- is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of s=13 TeV, corresponding to an integrated luminosity of 5.4 fb-1. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of m(Λ¯p)<2.8 GeV/c2. The branching fraction is measured to be Blow(B+→Λ¯pμ+μ-)=(1.70-0.56+0.65(stat)±0.17(syst)±0.14(ext))×10-8, where the last uncertainty is due to external inputs on B(B+→J/ψΛ¯p)×B(J/ψ→μ+μ-). With no significant signal observed in the high m(Λ¯p) region above 2.8 GeV/c2, an upper limit is set to be Bhigh(B+→Λ¯pμ+μ-)<2.8(3.7)×10-9 at the 90% (95%) confidence level.

UR - https://www.scopus.com/pages/publications/105047163186

U2 - 10.1103/pl88-4435

DO - 10.1103/pl88-4435

M3 - Article

C2 - 42606492

AN - SCOPUS:105047163186

SN - 0031-9007

VL - 137

JO - Physical Review Letters

JF - Physical Review Letters

IS - 5

M1 - 051801

ER -

Evidence for the Rare Decay B+ → Λ ̄ pμ+μ

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