Performance study of the relative decay width measurement in hadronic decays of Z boson at CEPC by using the template method

Abstract

The Circular Electron Positron Collider (CEPC) was proposed by the Chinese particle physics scientists as a future Higgs factory and [Formula: see text] factory. It will produced more than [Formula: see text] [Formula: see text] bosons by operating at a center-of-mass energy around 91.2 GeV in two years. In this study, the measurement of the relative decay widths of [Formula: see text] bosons decaying to [Formula: see text] quarks [Formula: see text], [Formula: see text] quarks [Formula: see text] and light quarks [Formula: see text] in hadronic [Formula: see text] decays are studied on CEPC Monte Carlo (MC) samples. By using a template method, [Formula: see text], [Formula: see text] and [Formula: see text] can be fitted from reconstructed data as the fractions of MC templates with different flavors. The distribution of a sensitive variable, [Formula: see text]-tagging probability, is used as the template, because of its high performance in discriminating different flavors. Based on the expected statistics of [Formula: see text] [Formula: see text] bosons at CEPC, the statistical uncertainty is estimated to be approximately [Formula: see text] by using the template method, which means that the measurement will no longer be limited by the statistics. Systematic errors arise directly from the difference in the [Formula: see text]-tagging probability distribution between real data and template MC samples. By considering the bias of input variables used for [Formula: see text]-tagging probability computing, the quantitative effect for each kind of input variable is investigated by using an ensemble test procedure.