Measurement of the ratio of the B_c⁺ → J/ψτ⁺ν_τ and B_c⁺ → J/ψ μ⁺ν_μ branching fractions using three-prong τ lepton decays

2025/10/24 by CMS Collaboration · 2 voices
#hep-ex

paper · pdf · doi:10.48550/arxiv.2510.21559

Abstract

The ratio between the B_c⁺ → J/ψτ⁺ν_τ and B_c⁺ → J/ψμ⁺ν_μ branching fractions is measured using a data sample of proton-proton collisions collected by CMS at a center-of-mass energy of 13 TeV in the years 2016-2018 and corresponding to an integrated luminosity of 138 fb^-1. The J/ψ meson is identified through its J/ψ → μ⁺μ^- decay and the tau lepton is reconstructed in the hadronic three-prong final state. The measured ratio of branching fractions in this tau decay mode, R^had_J/ψ = 1.04 _-0.44^+0.50, is combined with the previous analysis based on the τ⁺ → μ⁺ν_μν_τ leptonic decay channel, leading to R_J/ψ = 0.49 ± 0.26. As this result is consistent with the standard model prediction of 0.258 ± 0.004, no evidence of lepton flavor universality violation is found.

Discussions

• In particle physics and physics in general, some quantities are conserved for clear physical reasons . But some other things seem to be conserved even though there is no physics law prohibiting it.Thi [bsky, 6 points, 0 comments]
• 🤔 CMS also measure R(J/ψ) on the high side. That's the ratio of Bc⁺→J/ψτν to Bc⁺→J/ψμν. LHCb saw an excess compared to the Standard Model, now CMS has it too. arxiv.org/pdf/2510.21559 [bsky, 5 points, 1 comments]

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