Shabana Khan | Searcharxiv

arXiv2025

New physics effects in semileptonic $\bar{B_s} \to K^{*+}(\to Kπ) \ell^- \barν_\ell$ decay

We analyze the new physics effects in semileptonic $\bar{B_s} \to K^{*+}(\to Kπ) \ell^- \barν_\ell$ decay induced by the $b \to u \ell ν_{\ell}$ quark level transition. We consider the vector, scalar and tensor new physics Lorentz structures in addition to the SM in effective field theory approach. Constraints on new physics parameters are obtained from experimental observations of both semileptonic and leptonic decays of $B$ mesons, which are governed by the underlyng $b \to u \ell ν_\ell$ transition. We explore the new physics effects in differential branching fraction, lepton forward-backward asymmetry, fraction of longitudinal polarization of $K^*$ meson and normalized angular observables in $\bar{B_s} \to K^{*+}(\to Kπ) \ell^- \barν_\ell$ decay.

hep-ph↗

arXiv2023

Impact of $b \to c$ measurements on $Λ_b \to p τ\barν$ decay in $U_1$ leptoquark model

The measurements of several lepton flavor universality (LFU) violating observables in the decays induced by the quark level transition $b \to c τ\barν$ provide an inkling of plausible physics beyond the standard model of electroweak interactions. Such new physics would also impact other sectors. In this work, we estimate the leverage of new physics in $b \to c τ\barν$ on $Λ_b \to p τ\barν$ decay in the context of $U_1$ leptoquark model. In this model, the new physics couplings in $b \to u τ\barν$ transition can be written in terms of $b \to c τ\barν$ couplings and hence the extent of allowed new physics in $Λ_b \to p τ\barν$ would be determined by $b \to c τ\barν$ transition. Using the new physics parameter space obtained by performing a fit to all $b \to c τ\barν$ data, we obtain predictions of several $Λ_b \to p τ\barν$ observables. We find that the current $b \to c τ\barν$ data allows an order of magnitude enhancement in the branching ratio as well as in the LFU ratio. The other observables such as convexity parameter, lepton forward-backward asymmetry, longitudinal polarization of final state baryon and tau lepton are consistent with the SM value.

hep-ph↗