Search for the Lepton-Flavor Violating Decays B+ →π+μ±e∓

LHCb Collaboration

doi:10.1103/ln8k-mlhr

Search for the Lepton-Flavor Violating Decays B+ →π+μ±e∓

LHCb Collaboration

Science Park 105
Syracuse University
University of Warwick
Physik-Institut der Universität Zürich
University of Edinburgh
University of Liverpool
Universidade de Santiago de Compostela
University of Bristol
National Centre for Nuclear Research (NCBJ)
Department of Physics and Astronomy
Uppsala University
Université Paris-Saclay
University of Michigan, Ann Arbor
Clermont-Auvergne University
LNF-INFN
Fakultät Physik
University of Dortmund
Lamarr Institute for Machine Learning and Artificial Intelligence
Vilnius University
European Organization for Nuclear Research
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
University of Heidelberg

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Abstract

The first search for the lepton-flavor violating decays B+→π+μ±e∓ in proton-proton collisions is presented, using data collected by the LHCb experiment between 2011 and 2018, corresponding to an integrated luminosity of 9 fb-1. No significant signal is observed and an upper limit on the branching fraction is set at B(B+→π+μ±e∓)<1.8×10-9 at the 90% confidence level, 2 orders of magnitude more restrictive than the most stringent upper limit to date. This is the first constraint on lepton-flavor violating b→d quark transitions at the LHC and also sets the most stringent upper limits to date on b→dμ±e∓ transitions. Limits on left-handed and scalar scenarios beyond the standard model are also reported.

Original language	English
Article number	061802
Journal	Physical Review Letters
Volume	137
Issue number	6
DOIs	https://doi.org/10.1103/ln8k-mlhr
Publication status	Published - 7 Aug 2026

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@article{b0f232dbd7d442acb67eacdc5adc1800,

title = "Search for the Lepton-Flavor Violating Decays B+ →π+μ±e∓",

abstract = "The first search for the lepton-flavor violating decays B+→π+μ±e∓ in proton-proton collisions is presented, using data collected by the LHCb experiment between 2011 and 2018, corresponding to an integrated luminosity of 9 fb-1. No significant signal is observed and an upper limit on the branching fraction is set at B(B+→π+μ±e∓)<1.8{\texttimes}10-9 at the 90\% confidence level, 2 orders of magnitude more restrictive than the most stringent upper limit to date. This is the first constraint on lepton-flavor violating b→d quark transitions at the LHC and also sets the most stringent upper limits to date on b→dμ±e∓ transitions. Limits on left-handed and scalar scenarios beyond the standard model are also reported.",

author = "\{LHCb Collaboration\} and R. Aaij and M. Abdelfatah 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 S. Akar and K. Akiba and P. Albicocco and J. Albrecht and R. Aleksiejunas and F. Alessio and \{Alvarez Cartelle\}, P. 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 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 \{Bachiller Perea\}, I. and S. Bachmann and M. Bachmayer and V. Balagura and F. Fleuret and E. Maurice and Niel, \{E. M.\}",

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

year = "2026",

month = aug,

day = "7",

doi = "10.1103/ln8k-mlhr",

language = "English",

volume = "137",

journal = "Physical Review Letters",

issn = "0031-9007",

publisher = "American Physical Society",

number = "6",

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TY - JOUR

T1 - Search for the Lepton-Flavor Violating Decays B+ →π+μ±e∓

AU - LHCb Collaboration

AU - Aaij, R.

AU - Abdelfatah, M.

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 - Akar, S.

AU - Akiba, K.

AU - Albicocco, P.

AU - Albrecht, J.

AU - Aleksiejunas, R.

AU - Alessio, F.

AU - Alvarez Cartelle, P.

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 - Artuso, M.

AU - Aslanides, E.

AU - Ataíde Da Silva, R.

AU - Atzeni, M.

AU - Audurier, B.

AU - Authier, J. A.

AU - Bacher, D.

AU - Bachiller Perea, I.

AU - Bachmann, S.

AU - Bachmayer, M.

AU - Balagura, V.

AU - Fleuret, F.

AU - Maurice, E.

AU - Niel, E. M.

PY - 2026/8/7

Y1 - 2026/8/7

N2 - The first search for the lepton-flavor violating decays B+→π+μ±e∓ in proton-proton collisions is presented, using data collected by the LHCb experiment between 2011 and 2018, corresponding to an integrated luminosity of 9 fb-1. No significant signal is observed and an upper limit on the branching fraction is set at B(B+→π+μ±e∓)<1.8×10-9 at the 90% confidence level, 2 orders of magnitude more restrictive than the most stringent upper limit to date. This is the first constraint on lepton-flavor violating b→d quark transitions at the LHC and also sets the most stringent upper limits to date on b→dμ±e∓ transitions. Limits on left-handed and scalar scenarios beyond the standard model are also reported.

AB - The first search for the lepton-flavor violating decays B+→π+μ±e∓ in proton-proton collisions is presented, using data collected by the LHCb experiment between 2011 and 2018, corresponding to an integrated luminosity of 9 fb-1. No significant signal is observed and an upper limit on the branching fraction is set at B(B+→π+μ±e∓)<1.8×10-9 at the 90% confidence level, 2 orders of magnitude more restrictive than the most stringent upper limit to date. This is the first constraint on lepton-flavor violating b→d quark transitions at the LHC and also sets the most stringent upper limits to date on b→dμ±e∓ transitions. Limits on left-handed and scalar scenarios beyond the standard model are also reported.

UR - https://www.scopus.com/pages/publications/105047863716

U2 - 10.1103/ln8k-mlhr

DO - 10.1103/ln8k-mlhr

M3 - Article

C2 - 42628049

AN - SCOPUS:105047863716

SN - 0031-9007

VL - 137

JO - Physical Review Letters

JF - Physical Review Letters

IS - 6

M1 - 061802

ER -

Search for the Lepton-Flavor Violating Decays B+ →π+μ±e∓

Abstract

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