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

Science Park 105
University of Warwick
Physik-Institut der Universität Zürich
University of Liverpool
Syracuse University
Universidade de Santiago de Compostela
University of Bristol
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
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
NFN Sezione di Milano-Bicocca
University of Chinese Academy of Sciences
INFN Roma Tor Vergata
Consejo Nacional de Rectores (CONARE)
Kurchatov Institute
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

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
Publication status	Published - 1 Apr 2026

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 V. Balagura and F. Fleuret and E. Maurice and Niel, \{E. M.\}",

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

year = "2026",

month = apr,

day = "1",

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

language = "English",

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 - Balagura, V.

AU - Fleuret, F.

AU - Maurice, E.

AU - Niel, E. M.

PY - 2026/4/1

Y1 - 2026/4/1

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 - Article

AN - SCOPUS:105038107208

SN - 1126-6708

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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