Branching fraction measurement of the Λ → p μ − ν ¯ μ decay

Journal article

A measurement of the branching fraction for the decay Λ→pμ−ν¯μ is presented using pp collision data collected by the LHCb experiment at a centre-of-mass energy of 13 TeV. The analysis is based on data recorded between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb−1. The result is obtained using Λ → pμ− decays as a normalisation channel. The measured branching fraction is BΛ→pμ−ν¯μ=1.462±0.016±0.100±0.011×10−4, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalisation mode branching fraction, respectively. This result improves the precision of the branching fraction measurement by a factor of two compared to the previous best measurement and sets a more stringent bound on lepton flavour universality in s → u quark transitions. It is consistent with previous measurements, and the extracted lepton flavour universality test observable, Rμe=ΓΛ→pμ−ν¯μΓΛ→pe−ν¯e=0.175±0.012, agrees with the Standard Model prediction.

Authors: Aaij, R; Abdelmotteleb, ASW; Abellan Beteta, C; Abudinén, F; Ackernley, T

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Springer
• Journal: Journal of High Energy Physics
• Volume: 2026
• Issue: 4
• Article number: 96
• Publication date: 2026-04-14
• Acceptance date: 2026-02-23
• DOI: 10.1007/jhep04(2026)096
• EISSN: 1029-8479
• ISSN: 1126-6708
• Language: English
• Keywords: Branching fraction; Electroweak Interaction; Flavour Physics; Hadron-Hadron Scattering