The $Higgs\to b\bar{b}, c\bar{c}, gg$ measurement at CEPC

TL;DR

This paper evaluates the precision of Higgs boson decay measurements at the CEPC, highlighting how detector performance improvements can significantly enhance measurement accuracy for various decay channels.

Contribution

It provides detailed projections of Higgs decay signal strength accuracies at CEPC and analyzes the impact of detector performance on these measurements.

Findings

Signal strength of H→bb̄, cc̄, gg can be measured with sub-percent to few percent accuracy.

Improved flavor tagging significantly enhances measurement precision.

Better detector performance, especially in flavor tagging and CSI, substantially improves accuracy.

Abstract

Accurately measuring the properties of the Higgs boson is one of the core physics objectives of the Circular Electron Positron Collider (CEPC). As a Higgs factory, the CEPC is expected to operate at a centre-of-mass energy of $240\,GeV$, deliver an integrated luminosity of $5.6\,ab^{-1}$, and produce one million Higgs bosons according to the CEPC Conceptual Design Report (CDR). Combining measurements of the $\ell^+\ell^-H$, $\nu\bar{\nu} H$, and $q\bar{q}H$ channels, we conclude that the signal strength of $H\to b\bar{b}/c\bar{c}/gg$ can be measured with a relative accuracy (statistic uncertainty only) of 0.27\%/4.03\%/1.56\%. Extrapolating to the recently released TDR operating parameters corresponding to the integrated luminosity of $20\,ab^{-1}$, the relative accuracy of $H\to b\bar{b}/c\bar{c}/gg$ signal strength is 0.14\%/2.13\%/0.82\%. We analyze the dependence of the expected accuracies on the critical detector performances: Color Singlet Identification (CSI) for the $q\bar{q}H$ channel and flavor tagging for both $\nu\bar{\nu} H$ and $q\bar{q}H$ channels. We observe that compared to the baseline CEPC detector performance, ideal flavor tagging increases the $H\to b\bar{b}/c\bar{c}/gg$ signal strength accuracy by 2\%/63\%/13\% in the $\nu\bar{\nu} H$ channel and 35\%/122\%/181\% in the $q\bar{q}H$ channel. In addition, better performance of CSI can significantly improve the anticipated accuracy of signal strength. The relevant systematics are also discussed in this paper.