Analysis of $B_c \to \tau\nu_\tau$ at CEPC

TL;DR

This paper explores the potential of the CEPC collider to precisely measure the $B_c o au u_ au$ decay, which could significantly improve understanding of the Standard Model and constrain new physics with high accuracy.

Contribution

It provides a detailed analysis of the measurement prospects of $B_c o au u_ au$ at CEPC, including expected significance and precision, highlighting its potential for new physics constraints.

Findings

Achieves 5σ significance with ~10^9 Z decays

Signal strength can reach ~1% accuracy at CEPC

Potential to measure $|V_{cb}|$ with ~1% precision

Abstract

The precise determination of the $B_c \to \tau\nu_\tau$ branching ratio provides an advantageous opportunity for understanding the electroweak structure of the Standard Model, measuring the CKM matrix element $|V_{cb}|$ and probing new physics models. In this paper, we discuss the potential of measuring the processes of $B_c \to \tau\nu_\tau$ with $\tau$ decaying leptonically at the proposed Circular Electron Positron Collider (CEPC). We conclude that during the $Z$ pole operation, the channel signal can achieve five $\sigma$ significance with $\sim 10^9$ $Z$ decays, and the signal strength accuracies for $B_c \to \tau\nu_\tau$ can reach around 1% level at the nominal CEPC $Z$ pole statistics of one trillion $Z$ decays assuming the total $B_c \to \tau \nu_\tau$ yield is $3.6 \times 10^6$. Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for the $b \to c\tau\nu$ transition. If the total $B_c$ yield can be determined to $\mathcal{O}(1\%)$ level of accuracy in the future, these results also imply $|V_{cb}|$ could be measured up to $\mathcal{O}(1\%)$ level of accuracy.