Study of new physics effects in B¯s→D(∗)sτ−ν¯τ semileptonic decays using lattice QCD form factors and heavy quark effective theory

Abstract

We benefit from the lattice QCD determination of the Standard Model (SM) form factors for the B¯s→D∗s and B¯s→Ds semileptonic decays carried out by the HPQCD collaboration in Refs. Phys. Rev. D 105, 094506 (2022) and Phys. Rev. D 101, 074513 (2020), and the heavy quark effective theory (HQET) relations for the analogous B→D(∗) decays obtained by F.U. Bernlochner et al. in Phys. Rev. D 95, 115008 (2017), to extract the leading and sub-leading Isgur-Wise functions for the B¯s→D(∗)s decays. Further use of the HQET relations allows us to evaluate the corresponding scalar, pseudoscalar and tensor form factors needed for a phenomenological study of new physics (NP) effects on the B¯s→D(∗)s semileptonic decay. At present, the experimental values for the ratios RD(∗)=Γ[B¯→D(∗)τ−ν¯τ]/Γ[B¯→D(∗)e−(μ−)ν¯e(μ)] are the best signal in favor of lepton flavor universality violation (LFUV) seen in charged current (CC) b→c decays. In this work we conduct a study of NP effects on the B¯s→D(∗)sτ−ν¯τ semileptonic decays by comparing tau spin, angular and spin-angular asymmetry distributions obtained within the SM and three different NP scenarios. As expected from SU(3) light-flavor symmetry, we get results close to the ones found in a similar analysis of the B¯→D(∗) case. The measurement of the B¯s→D(∗)sℓν¯ℓ semileptonic decays, which is within reach of present experiments, could then be of relevance in helping to establish or rule out LFUV in CC b→c transitions.

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ORCID for Jonathan M. Flynn: orcid.org/0000-0002-6280-1677

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