Differential decay rate of B+→ J/ψK+ with the LHCb Upgrade I experiment

The LHCb collaboration

doi:10.1007/JHEP04(2026)170

Differential decay rate of B⁺→ J/ψK⁺ with the LHCb Upgrade I experiment

The LHCb collaboration

National Institute for Subatomic Physics
University of Warwick
University of Zurich
University of Liverpool
Syracuse University
Instituto Galego de Física de Altas Enerxías (IGFAE)
University of Bristol
Uppsala University
Université Paris-Saclay
University of Michigan, Ann Arbor
Université Clermont Auvergne
AGH University of Krakow
National Institute for Nuclear Physics
TU Dortmund University
Vilnius University
CERN
University of Cambridge
Sorbonne Université
Universidade Federal do Rio de Janeiro
Peking University
University of A Coruna
NFN Sezione di Milano-Bicocca
University of Chinese Academy of Sciences
Consejo Nacional de Rectores (CONARE)
Institute for High Energy Physics
CPPM
Swiss Federal Institute of Technology Lausanne
Massachusetts Institute of Technology
Laboratoire Leprince-Ringuet
University of Oxford
Heidelberg University
Ruhr University Bochum
Centro Brasileiro de Pesquisas Físicas
Pontifícia Universidade Católica do Rio de Janeiro
University of Manchester
University of Edinburgh
CAS - Institute of High Energy Physics
Lomonosov Moscow State University
Ramon Llull University
Kyiv National Taras Shevchenko University
Eötvös Loránd University
Henryk Niewodniczanski Institute of Nuclear Physics of the Polish Academy of Sciences
University of Bonn
Imperial College London
Université Savoie Mont Blanc
Higher School of Economics
Los Alamos National Laboratory
Maastricht University
Monash University
RAS - Saint Petersburg Nuclear Physics Institute
Cracow University of Technology
Ohio State University
Wuhan University
University of Barcelona
Tsinghua University
NASU - Institute of Nuclear Research
Horia Hulubei National Institute of Physics and Nuclear Engineering
University of Glasgow
University of Cincinnati
National University of Science and Technology "MISiS"
Hunan University
University of Groningen
Central China Normal University
University College Dublin
South China Normal University
Rutherford Appleton Laboratory
Alikhanov Institute for Theoretical and Experimental Physics
University of Valencia
University of Maryland, College Park
RAS - Institute for Nuclear Research
NASU - Kharkov Institute of Physics and Technology
University of Freiburg
National Centre for Nuclear Research
RWTH Aachen University
Universidad Nacional de Colombia
Czech Academy of Sciences
University of Birmingham
Tomsk Polytechnic University
Vrije Universiteit Amsterdam
RAS - Budker Institute of Nuclear Physics
Yandex School of Data Analysis
Henan Normal University
Lanzhou University
Russian Research Centre Kurchatov Institute
Max Planck Institute for Nuclear Physics
Universidad Andrés Bello

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

Abstract

The normalised decay rate of B⁺ → J/ψ(→ μ⁺μ⁻)K⁺ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb⁻¹ collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, A_FB, and the flatness parameter, F_H, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ⁺μ⁻ and b → dμ⁺μ⁻ transitions, which are particularly sensitive to physics beyond the Standard Model.

Original language	English
Article number	170
Journal	Journal of High Energy Physics
Volume	2026
Issue number	4
DOIs	https://doi.org/10.1007/JHEP04(2026)170
State	Published - Apr 2026
Externally published	Yes

Keywords

B Physics
Flavour Physics
Hadron-Hadron Scattering
Rare Decay

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10.1007/JHEP04(2026)170

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title = "Differential decay rate of B+→ J/ψK+ with the LHCb Upgrade I experiment",

abstract = "The normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb−1 collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, AFB, and the flatness parameter, FH, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ+μ− and b → dμ+μ− transitions, which are particularly sensitive to physics beyond the Standard Model.",

keywords = "B Physics, Flavour Physics, Hadron-Hadron Scattering, Rare Decay",

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 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 \{Bachiller Perea\}, I. and S. Bachmann and M. Bachmayer and \{Calderon Ramirez\}, S.",

note = "Publisher Copyright: {\textcopyright} The Author(s) 2026.",

year = "2026",

month = apr,

doi = "10.1007/JHEP04(2026)170",

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

volume = "2026",

journal = "Journal of High Energy Physics",

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T1 - Differential decay rate of B+→ J/ψK+ with the LHCb Upgrade I experiment

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 - 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 - Bachiller Perea, I.

AU - Bachmann, S.

AU - Bachmayer, M.

AU - Calderon Ramirez, S.

PY - 2026/4

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N2 - The normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb−1 collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, AFB, and the flatness parameter, FH, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ+μ− and b → dμ+μ− transitions, which are particularly sensitive to physics beyond the Standard Model.

AB - The normalised decay rate of B+ → J/ψ(→ μ+μ−)K+ is measured as a function of the lepton helicity angle using a data sample corresponding to an integrated luminosity of 1.1 fb−1 collected during October 2024 with the upgraded (Upgrade I) LHCb detector. This angular distribution can be parameterised by two coefficients, the forward-backward asymmetry, AFB, and the flatness parameter, FH, whose values are constrained by conservation of angular momentum. These coefficients are measured both integrated and differentially across various kinematic and detector-response variables, and the results are found to be in good agreement with expectations. These measurements show that the detector response of the LHCb Upgrade I experiment is understood to the precision required to reliably extract the angular coefficients associated with rare b → sμ+μ− and b → dμ+μ− transitions, which are particularly sensitive to physics beyond the Standard Model.

KW - B Physics

KW - Flavour Physics

KW - Hadron-Hadron Scattering

KW - Rare Decay

UR - https://www.scopus.com/pages/publications/105038107208

U2 - 10.1007/JHEP04(2026)170

DO - 10.1007/JHEP04(2026)170

M3 - Artículo

AN - SCOPUS:105038107208

SN - 1029-8479

VL - 2026

JO - Journal of High Energy Physics

JF - Journal of High Energy Physics

IS - 4

M1 - 170

ER -

Differential decay rate of B⁺→ J/ψK⁺ with the LHCb Upgrade I experiment

Abstract

Keywords

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