Probing the top quark flavor-changing couplings at CEPC * * Supported by CNRS via the LIA FCPPL, by the CEPC theory study grant, and by IHEP (Y7515540U1)

Cen Zhang,Liaoshan Shi

doi:10.1088/1674-1137/43/11/113104

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.

Highlights

After the discovery of the Higgs boson [1, 2], the focus of high energy physics turned to the study of its detailed properties
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

Summary

Introduction

After the discovery of the Higgs boson [1, 2], the focus of high energy physics turned to the study of its detailed properties. The Circular Electron Positron Collider (CEPC) in China [4, 5] is proposed to run as a Higgs factory at 240 GeV, which maximizes the e+e− → HZ cross-section, producing at least a million Higgs bosons over a period of 7 years. By virtue of its large mass, it is often thought of as a window to new physics. Producing top quark pairs at a lepton collider would, require a minimum center-of-mass energy of about 2mtop ≈ 345 GeV, beyond the currently planned CEPC energy

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Conclusion