Measurement of the branching fraction ratio RK at large dilepton invariant mass

The LHCb collaboration

doi:10.1007/JHEP07(2025)198

Measurement of the branching fraction ratio R_K at large dilepton invariant mass

The LHCb collaboration

National Institute for Subatomic Physics
University of Warwick
University of Zurich
University of Liverpool
Syracuse University
University of Santiago de Compostela
University of Bristol
Department of Physics and Astronomy
Uppsala University
Université Paris-Saclay
University of Michigan, Ann Arbor
Université Clermont Auvergne
National Institute for Nuclear Physics
Fakultät Physik
TU Dortmund University
Lamarr Institute for Machine Learning and Artificial Intelligence
CERN
Department of Physics and Astronomy
University of Manchester
University of Cambridge
Sorbonne Université
Universidade Federal do Rio de Janeiro
Peking University
University of Milan - Bicocca
University of Chinese Academy of Sciences
University of Rome Tor Vergata
Consejo Nacional de Rectores (CONARE)
CPPM
Institute of Physics
Swiss Federal Institute of Technology Lausanne
Massachusetts Institute of Technology
University of Oxford
Université Savoie Mont Blanc
Heidelberg University
Laboratoire Leprince-Ringuet

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

6 Scopus citations

Abstract

A test of lepton universality between muons and electrons is performed using B⁺ → K⁺ℓ⁺ℓ⁻ decays (where ℓ = e, μ), in the dilepton invariant-mass-squared region above 14.3 GeV²/c⁴. The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 fb⁻¹, collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for B⁺→ K⁺μ⁺μ⁻ and B⁺→ K⁺e⁺e⁻ decays is measured to be RK=1.08−0.09+0.11stat−0.04+0.04syst, which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using B⁺ → K⁺ℓ⁺ℓ⁻ decays with dilepton invariant-mass-squared above the ψ(2S) mass, whilst being the first of its kind at a hadron collider.

Original language	English
Article number	198
Journal	Journal of High Energy Physics
Volume	2025
Issue number	7
DOIs	https://doi.org/10.1007/JHEP07(2025)198
State	Published - Jul 2025
Externally published	Yes

Keywords

B Physics
Flavour Changing Neutral Currents
Flavour Physics
Hadron-Hadron Scattering

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10.1007/JHEP07(2025)198

Cite this

@article{f289a7b481004864a57aa817299384cf,

title = "Measurement of the branching fraction ratio RK at large dilepton invariant mass",

abstract = "A test of lepton universality between muons and electrons is performed using B+ → K+ℓ+ℓ− decays (where ℓ = e, μ), in the dilepton invariant-mass-squared region above 14.3 GeV2/c4. The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1, collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for B+→ K+μ+μ− and B+→ K+e+e− decays is measured to be RK=1.08−0.09+0.11stat−0.04+0.04syst, which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using B+ → K+ℓ+ℓ− decays with dilepton invariant-mass-squared above the ψ(2S) mass, whilst being the first of its kind at a hadron collider.",

keywords = "B Physics, Flavour Changing Neutral Currents, Flavour Physics, Hadron-Hadron Scattering",

author = "\{The 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 P. Albicocco and J. Albrecht and F. Alessio and Z. Aliouche 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 A. Andreianov and P. Andreola and M. Andreotti and D. Andreou and A. Anelli and D. Ao and F. Archilli and M. Argenton and \{Arguedas Cuendis\}, S. and A. Artamonov and M. Artuso and E. Aslanides and \{Ata{\'i}de Da Silva\}, R. and M. Atzeni and B. Audurier and D. Bacher and \{Bachiller Perea\}, I. and S. Bachmann and M. Bachmayer and Back, \{J. J.\} and \{Baladron Rodriguez\}, P. and V. Balagura and A. Balboni and \{Calderon Ramirez\}, S.",

note = "Publisher Copyright: {\textcopyright} The Author(s) 2025.",

year = "2025",

month = jul,

doi = "10.1007/JHEP07(2025)198",

language = "Ingl{\'e}s",

volume = "2025",

journal = "Journal of High Energy Physics",

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T1 - Measurement of the branching fraction ratio RK at large dilepton invariant mass

AU - The 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 - Albicocco, P.

AU - Albrecht, J.

AU - Alessio, F.

AU - Aliouche, Z.

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 - Andreianov, A.

AU - Andreola, P.

AU - Andreotti, M.

AU - Andreou, D.

AU - Anelli, A.

AU - Ao, D.

AU - Archilli, F.

AU - Argenton, M.

AU - Arguedas Cuendis, S.

AU - Artamonov, A.

AU - Artuso, M.

AU - Aslanides, E.

AU - Ataíde Da Silva, R.

AU - Atzeni, M.

AU - Audurier, B.

AU - Bacher, D.

AU - Bachiller Perea, I.

AU - Bachmann, S.

AU - Bachmayer, M.

AU - Back, J. J.

AU - Baladron Rodriguez, P.

AU - Balagura, V.

AU - Balboni, A.

AU - Calderon Ramirez, S.

PY - 2025/7

Y1 - 2025/7

N2 - A test of lepton universality between muons and electrons is performed using B+ → K+ℓ+ℓ− decays (where ℓ = e, μ), in the dilepton invariant-mass-squared region above 14.3 GeV2/c4. The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1, collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for B+→ K+μ+μ− and B+→ K+e+e− decays is measured to be RK=1.08−0.09+0.11stat−0.04+0.04syst, which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using B+ → K+ℓ+ℓ− decays with dilepton invariant-mass-squared above the ψ(2S) mass, whilst being the first of its kind at a hadron collider.

AB - A test of lepton universality between muons and electrons is performed using B+ → K+ℓ+ℓ− decays (where ℓ = e, μ), in the dilepton invariant-mass-squared region above 14.3 GeV2/c4. The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1, collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for B+→ K+μ+μ− and B+→ K+e+e− decays is measured to be RK=1.08−0.09+0.11stat−0.04+0.04syst, which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using B+ → K+ℓ+ℓ− decays with dilepton invariant-mass-squared above the ψ(2S) mass, whilst being the first of its kind at a hadron collider.

KW - B Physics

KW - Flavour Changing Neutral Currents

KW - Flavour Physics

KW - Hadron-Hadron Scattering

UR - https://www.scopus.com/pages/publications/105018455053

U2 - 10.1007/JHEP07(2025)198

DO - 10.1007/JHEP07(2025)198

M3 - Artículo

AN - SCOPUS:105018455053

SN - 1029-8479

VL - 2025

JO - Journal of High Energy Physics

JF - Journal of High Energy Physics

IS - 7

M1 - 198

ER -

Measurement of the branching fraction ratio R_K at large dilepton invariant mass

Abstract

Keywords

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