Investigating $ \Upsilon(ns) \to \tau^+ \tau^- $ decay in the Leptoquark scenario

TL;DR

This paper explores how leptoquark models could explain deviations from the Standard Model in lepton flavor universality tests involving $$ meson and $$ decay processes, especially focusing on $$ decays to $ au$ leptons.

Contribution

It performs a $$ fit to constrain new physics parameters and investigates their effects on $$ decay observables within various leptoquark models.

Findings

Constraints on new physics couplings from experimental data.

Predictions for branching ratios and LFU parameters under leptoquark scenarios.

Potential explanations for observed deviations from the Standard Model.

Abstract

Several measurements on $R_D, R_{D^*}$, and $R_{J/ \psi}$ by the BaBar, Belle, and LHCb experiments show significant deviations from their Standard Model (SM) predictions, which illustrate the fact that the concept of lepton flavor universality (LFU) is violated in semileptonic $B$ meson as well as leptonic $\Upsilon(ns)(n=1,2,3)$ decays. Recently BaBar experiment announced that at $1.8\sigma$ level, $R_\Upsilon(3s)= {\rm Br}(\Upsilon(3s) \to \tau \bar{\tau})/{\rm Br}(\Upsilon(3s) \to \mu \bar{\mu})$ shows an acceptance with the SM. These fascinating findings point towards the possible implication of new physics in the $b \to c \tau \bar{\nu}$ transitions, which in turn, creates a new direction to look for new physics in $b \bar{b} \to \tau \bar{\tau} $ process. Thereby, the new physics contributions to the $b \to c \tau \bar{\nu}$ process would inevitably alter the $b \bar{b} \to \tau \bar{\tau} $ transitions. Here we conduct a $\chi^{2}$ fit to constraining the new parameters by using the measured values of $ R_D$, $R{_D*}$, $ R_{J/ \psi}$, $ R_{X_C}$, $F_L (D^*)$ and $P_{\tau} (D^*)$. In this context, we investigate the effect of constrained new physics couplings on the branching ratios and LFU parameters $R_{\Upsilon(ns)}$ through leptoquark models such as $S_3, \tilde{S_1}, \tilde{R_2}, U_1, U_3 $ and $ V_2$.