# Probing the top quark flavor-changing couplings at CEPC

## TL;DR

This paper explores how the future CEPC collider can significantly improve constraints on top quark flavor-changing neutral couplings, surpassing current bounds and offering detailed insights into top quark flavor properties.

## Contribution

It systematically analyzes all 56 flavor-changing parameters of the top quark and demonstrates CEPC's superior sensitivity compared to existing and future colliders.

## Key findings

- CEPC can improve limits on four-fermion flavor-changing coefficients by 10-100 times.
- CEPC's sensitivity to two-fermion flavor-changing couplings is comparable to current bounds.
- c-jet tagging enhances CEPC's ability to identify top-charm flavor-changing interactions.

## Abstract

We propose to study the flavor properties of the top quark at the future Circular Electron Positron Collider (CEPC) in China. We systematically consider the full set of 56 real parameters that characterize the flavor-changing neutral interactions of the top quark, which can be tested at CEPC in the single top production channel. Compared with the current bounds from the LEP2 data and the projected limits at the high-luminosity LHC, we find that CEPC could improve the limits of the four-fermion flavor-changing coefficients by one to two orders of magnitude, and would also provide similar sensitivity for the two-fermion flavor-changing coefficients. Overall, CEPC could explore a large fraction of currently allowed parameter space that will not be covered by the LHC upgrade. We show that the $c$-jet tagging capacity at CEPC could further improve its sensitivity to top-charm flavor-changing couplings. If a signal is observed, the kinematic distribution as well as the $c$-jet tagging could be exploited to pinpoint the various flavor-changing couplings, providing valuable information about the flavor properties of the top quark.