Probing Lepton Flavour Universality with Λ_b decays to τ⁺τ^- final states

2025/11/07 by Bordone, Marzia, Isidori, Gino, Mayer, Christiane +1
Physics and Astronomy · Computer Science · #Particle physics theoretical and experimental studies #Computational Physics and Python Applications #Neutrino Physics Research

paper · doi:10.48550/arxiv.2511.05654

Abstract

We present a study of the rare baryonic decay Λ_b → Λτ⁺ τ^- as a probe of new physics (NP) coupled preferentially to third-generation fermions. Within the Standard Model, we evaluate the branching ratio and the lepton-flavour-universality (LFU) ratio R_Λ^τ/μ, including both perturbative and long-distance charm contributions. We show that the LFU ratio can be predicted with an uncertainty below 10%. Possible NP effects arising from lepton non-universal dynamics are analysed within an effective field theory framework motivated by the current anomalies in b → cτν and b → sμ⁺μ^- transitions. In this context, R_Λ^τ/μ can be enhanced by several orders of magnitude, offering a clear target for upcoming searches. The implications for the related mode Λ_b → pKτ⁺τ^- are also briefly discussed.

Citations

• Charm rescattering in B⁰→ K⁰ℓℓ: an improved analysis
• Search for B⁰ → K^{∗ 0} τ⁺ τ^- decays at the Belle II experiment
• Short- vs. long-distance physics in B→ K^(*) ℓ⁺ℓ^-: a data-driven analysis
• New Physics in the Third Generation: A Comprehensive SMEFT Analysis and Future Prospects
• Lepton universality violation and lepton flavor conservation in B-meson decays

Related

• Lepton flavour universality tests in b → c l ν decays at the LHCb experiment
• Lepton Flavour Universality in τ decays
• Delving into new physics in semileptonic b → c τ ν transitions
• Probing the Λ_b→ Λ_c^*τν_τ decays with leptoquarks
• τ physics at LHCb