Top quark mass measurements at the $t\bar{t}$ threshold with CEPC

TL;DR

This study evaluates the precision of top quark mass, width, and strong coupling constant measurements at the CEPC collider through a detailed energy scan near the $tar{t}$ threshold, considering realistic experimental conditions.

Contribution

It introduces optimized scan strategies for measuring top quark properties at CEPC, achieving high precision with limited luminosity and accounting for various uncertainties.

Findings

Top quark mass can be measured with 9-14 MeV precision.

Top quark width can be measured with 26 MeV precision.

The strong coupling constant $oldsymbol{ extalpha_S}$ can be measured with 0.00039 precision.

Abstract

We present a study of top quark mass measurements at the $t\bar{t}$ threshold based on CEPC. A centre-of-mass energy scan near two times of the top mass is performed and the measurement precision of top quark mass, width and $\alpha_S$ are evaluated using the $t\bar{t}$ production rates. Realistic scan strategies at the threshold are discussed to maximise the sensitivity to the measurement of the top quark properties individually and simultaneously in the CEPC scenarios assuming a limited total luminosity of 100 fb$^{-1}$. With the optimal scan for individual property measurements, the top quark mass precision is expected to be 9 MeV, the top quark width precision is expected to be 26 MeV, and $\alpha_S$ can be measured at a precision of 0.00039. Taking into account the uncertainties from theory, background subtraction, beam energy and luminosity spectrum, the top quark mass can be measured at a precision of 14 MeV optimistically and 34 MeV conservatively at CEPC.