Test of lepton flavor universality in semileptonic ; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msubsup><mml:mi>B</mml:mi><mml:mi>c</mml:mi><mml:mo>+</mml:mo></mml:msubsup></mml:math>; meson decays in proton-proton collisions at ; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>13</mml:mn><mml:mtext> </mml:mtext><mml:mtext> </mml:mtext><mml:mi>TeV</mml:mi></mml:math> | CU Experts

A measurement of the ratio of branching fractions R(J/ψ)=B(Bc+→J/ψτ+ντ)/B(Bc+→J/ψμ+νμ) in the J/ψ→μ+μ−, τ+→μ+νμν¯τ decay channel is presented. This measurement uses a sample of proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment in 2018, corresponding to an integrated luminosity of 59.7 fb−1. The measured ratio, R(J/ψ)=0.17−0.17+0.18(stat)−0.22+0.21(syst)−0.18+0.19(theo)=0.17±0.33, agrees with the value of 0.2582±0.0038 predicted by the standard model, which assumes lepton flavor universality. By testing lepton flavor universality, this measurement is a probe of new physics using Bc+ mesons, which are currently only produced at the LHC.; ; ; ; ; © 2025 CERN, for the CMS Collaboration; 2025; CERN; ; ;

Hayrapetyan A; Tumasyan A; Adam W; Andrejkovic JW; Bergauer T; Chatterjee S; Damanakis K; Dragicevic M; Hussain PS; Jeitler M

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