$\Lambda_b \to (\Lambda_c,\,p)\,\tau\,\nu$ decays within standard model and beyond

TL;DR

This paper investigates $Lambda_b o (Lambda_c, p) au u$ decays within and beyond the Standard Model, analyzing experimental anomalies in B meson decays and predicting observables under new physics scenarios.

Contribution

It employs an effective Lagrangian approach to study $Lambda_b$ decays, constrains new physics parameters with existing data, and provides predictions for observables in various new physics models.

Findings

Constraints on new physics parameters from experimental data.

Predictions for decay branching ratios and ratios under different scenarios.

Analysis of deviations from Standard Model expectations.

Abstract

Deviations from the standard model prediction have been observed in several leptonic and semileptonic $B$ meson decays to $\tau\nu$ final states mediated via $b \to u$ and $b \to c$ charged current interactions. The measured value of ratio of branching ratios $R_{\pi}^l$ of $B^- \to \tau^-\,\nu_{\tau}$ to $B^0 \to \pi^+\,\l^-\,\nu$ decays, where $l = (e,\,\mu)$, is larger than the standard model prediction by more than a factor of two. Similarly, a combined excess of $3.9\sigma$ from the standard model expectation has been reported by HFAG for the values of $R_D$ and $R_{D^{\ast}}$, where $R_{D,\,D^{\ast}}$ represents the ratio of branching ratios of $B \to (D,\,D^{\ast})\,\tau\nu$ to corresponding $B \to (D,\,D^{\ast})\,l\nu$ decays, respectively. Very recently, hint of lepton flavor violation has been observed in the ratio of branching fractions of $B \to K\,e^+\,e^-$ to $B \to K\,\mu^+\,\mu^-$ decays as well. In this context, we employ an effective Lagrangian approach to study the decay branching fractions and the ratio of branching fractions of $\Lambda_b \to \Lambda_c\,l\,\nu$ and $\Lambda_b \to p\,l\,\nu$ decays within the standard model and beyond. We constrain the new physics parameter space using the existing experimental data on $R_D$, $R_{D^{\ast}}$, and $R_{\pi}^l$. We give predictions for various observables in the context of various new physics scenarios.