$\Lambda_b\to\Lambda_c\tau\bar\nu_\tau$ decay in scalar and vector leptoquark scenarios

TL;DR

This paper investigates how scalar and vector leptoquark models, proposed to explain B-meson decay anomalies, affect the $Lambda_b o Lambda_c au ar{ u}_ au$ decay, providing predictions for future experimental tests.

Contribution

It analyzes the impact of scalar and vector leptoquark scenarios on $Lambda_b$ decay observables, offering predictions to distinguish these models from the Standard Model and each other.

Findings

Both scenarios predict similar enhancements in decay rates.

Best-fit solutions are indistinguishable between the two scenarios.

Predictions align with Standard Model for polarization and asymmetry observables.

Abstract

It has been shown that the anomalies observed in $\bar B\to D^{(\ast)}\tau\bar\nu_\tau$ and $\bar B\to \bar K\ell^+\ell^-$ decays can be resolved by adding a single scalar or vector leptoquark to the Standard Model, while constraints from other precision measurements in the flavour sector can be satisfied without fine-tuning. To further explore these two interesting scenarios, in this paper, we study their effects in the semi-leptonic $\Lambda_b\to\Lambda_c\tau\bar\nu_\tau$ decay. Using the best-fit solutions for the operator coefficients allowed by the current data of mesonic decays, we find that (i) the two scenarios give similar amounts of enhancements to the branching fraction $\mathcal B(\Lambda_b\to\Lambda_c\tau\bar\nu_\tau)$ and the ratio $R_{\Lambda_c}=\mathcal B(\Lambda_b\to\Lambda_c \tau\bar\nu_\tau)/\mathcal B(\Lambda_b\to\Lambda_c\ell\bar\nu_\ell)$, (ii) the two best-fit solutions in each of these two scenarios are also indistinguishable from each other, (iii) both scenarios give nearly the same predictions as those of the Standard Model for the longitudinal polarizations of $\Lambda_c$ and $\tau$ as well as the lepton-side forward-backward asymmetry. With future measurements of these observables in $\Lambda_b\to\Lambda_c\tau\bar\nu_\tau$ decay at the LHCb, the two leptoquark scenarios could be further tested, and even differentiated from the other NP explanations for the $R_{D^{(\ast)}}$ anomalies. We also discuss the feasibility for the measurements of these observables at the LHC and the future $e^+e^-$ colliders.