Probing lepton universality with (semi)-leptonic B decays

The most recent measurements of the observables R_{D^{(*)}}RD(*) are in tension with the Standard Model offering hints of New Physics in b\rightarrow c \ell \bar{\nu}_{\ell}b→cℓν‾ℓ transitions. Motivated by these results, in this work we present an analysis on their b\rightarrow u \ell \bar{\nu}_{\ell}b→uℓν‾ℓ counterparts (for \ell=e, ~\mu, ~\tauℓ=e,μ,τ). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic BB decays (B^-\rightarrow \ell^- \bar{\nu}_{\ell}B−→ℓ−ν‾ℓ, \bar{B}\rightarrow \pi \ell \bar{\nu}_{\ell}B‾→πℓν‾ℓ and \bar{B}\rightarrow \rho \ell \bar{\nu}_{\ell}B‾→ρℓν‾ℓ). Here a key role is played by the leptonic BB processes, which are highly sensitive to new pseudoscalar interactions. In particular, we take advantage of the most recent measurement of the branching fraction of the channel B^-\rightarrow \mu^-\bar{\nu}_{\mu}B−→μ−ν‾μ by the Belle collaboration. Secondly, we extract the CKM matrix element |V_{ub}||Vub| while accounting simultaneously for New Physics contributions. Finally, we provide predictions for the branching fractions of yet unmeasured leptonic and semileptonic BB decays.