Implications of new physics in the decays $B_c \to (J/\psi,\eta_c)\tau\nu$

TL;DR

This paper investigates $B_c$ meson decays into charmonium states with tau leptons, calculating form factors and exploring potential new physics effects through an extended effective Hamiltonian.

Contribution

It introduces a comprehensive analysis of $B_c$ semileptonic decays including new physics operators and provides constraints on Wilson coefficients based on experimental data.

Findings

Predicted branching fractions for $B_c$ decays into $J/\psi$ and $\eta_c$ with tau leptons.

Constraints on new physics Wilson coefficients from current experimental data.

Potential polarization observables sensitive to new physics effects.

Abstract

We study the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond. The relevant hadronic transition form factors are calculated in the framework of the covariant confined quark model developed by us. We focus on the tau mode of these decays, which may provide some hints of new physics effects. We extend the standard model by assuming a general effective Hamiltonian describing the $b\to c\tau\nu$ transition, which consists of the full set of the four-fermion operators. We then obtain experimental constraints on the Wilson coefficients corresponding to each operator and provide predictions for the branching fractions and other polarization observables in different new physics scenarios.