Prospects of measuring $$R_b$$ in hadronic $$\mathrm{Z}$$ decays at the CEPC

Abstract

With an integrated luminosity of 45 $$\mathrm{ab}^{-1}$$ at $$\sqrt{s} = 91.2$$ GeV, more than $$10^{12}$$ $$\mathrm{Z}$$ bosons will be produced at the Circular Electron Positron Collider (CEPC). As a real $$\mathrm{Z}$$ boson factory, the precise study of $$\mathrm{Z}$$ boson physics can be achieved. In this paper, the relative partial width, $$R_{b}$$ , of $$\mathrm{Z}$$ boson into b quarks, is measured on the CEPC Monte Carlo level. Based on the latest CEPC detector concept, the $$\mathrm{Z}$$ hadronic decay channel is simulated and reconstructed by the CEPC software framework. By using the double-tagging method, $$R_b$$ can be solved from several equations referring to the ratios of b-tagged jet hemispheres in $$\mathrm{Z}$$ hadronic events. With the high performance of the b-tagging algorithm for CEPC, the b-tagging correlation between the two jet hemispheres can be reduced. By carrying out a closure test, the double-tagging method is verified to work well as we expected. We further estimated the dependence of systematic errors on the b-tagging efficiencies of the charm and light jet, as well as the b-tagging correlation between two jet hemispheres. The sources of systematic errors, such as physics modeling and hemisphere correlation, are investigated and studied preliminarily. Several kinds of error sources related to the hemisphere correlation are studied with the characterized variables.