Evidence for the rare decay B⁺ → Λp μ⁺ μ^-

2026/01/11 by LHCb collaboration, R. Aaij, Carlos Abellán Beteta +1212 · 2 voices
Physics and Astronomy · #Neutrino Physics Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #hep-ex

paper · pdf · doi:10.1103/pl88-4435

published as Phys. Rev. Lett. 137 (2026) 051801 · All figures and tables, along with any supplementary material and additional information, are available at https://lhcb-glance.cern.ch/alcm/public/analysis/full-details/5370

arxiv published 2026/01/11 · openalex publication_date 2026/03/24 · openalex created_date 2026/03/25 · arxiv created 2026/07/29 · arxiv updated 2026/07/29 · openalex updated_date 2026/07/30

Abstract

A search for the rare decay B⁺ → Λp μ⁺ μ^- is performed using proton-proton collision data recorded by the LHCb experiment at a center-of-mass energy of √(s)= 13 TeV, corresponding to an integrated luminosity of 5.4 fb^-1. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the low invariant-mass region of m( Λp)<2.8 GeV/c². The branching fraction is measured to be \cal B_{\rm low}(B⁺→ Λp μ⁺ μ^-)=(1.70 ^+0.65_-0.56(\rm stat) ± 0.17(\rm syst) ± 0.14(\rm ext)) × 10^-8, where the last uncertainty is due to external inputs on \cal B(B⁺→J/ψ Λp)× \cal B(J/ψ→μ⁺μ^-). With no significant signal observed in the high m( Λp) region above 2.8 GeV/c², an upper limit is set to be \cal B_{\rm high}(B⁺→ Λp μ⁺ μ^-)<2.8 (3.7) × 10^-9 at the 90% (95%) confidence level.

Citations

• A Decision-Theoretic Generalization of On-Line Learning and an Application to Boosting
• The Large-Sample Distribution of the Likelihood Ratio for Testing Composite Hypotheses
• Review of Particle Physics
• The LHCb Stripping Project: Sustainable Legacy Data Processing for High-Energy Physics
• Minimal Flavor Violation
• Geant4 developments and applications
• Sensitivity of searches for new signals and its optimization
• Presentation of search results: theCLstechnique
• A complete analysis of FCNC and CP constraints in general SUSY extensions of the standard model

Discussions

• Evidence for the rare decay B⁺→Λ̅pμ⁺μ⁻ arxiv.org/abs/2601.06878 - In the low invariant-mass region of m(Λ̅p)<2.8 GeV, the branching fraction is measured to be (1.70+0.65−0.56(stat)±0.17(syst)±0.14(ext [bsky, 2 points, 0 comments]
• #LHCbpaper: Evidence for the rare decay B⁺ → Λ̅p μ⁺μ⁻ (arXiv:2601.06878) https://arxiv.org/abs/2601.06878 [bsky, 1 points, 0 comments]

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• An analysis of Λ_b⁰ → Λμ⁺μ^- decays at the LHCb experiment