Lepton identification performance in Jets at a future electron positron Higgs Z factory

TL;DR

This paper evaluates the lepton identification performance within jets at a future electron-positron Higgs/Z factory, demonstrating high efficiency and purity, and analyzing factors affecting performance degradation.

Contribution

It provides the first detailed analysis of jet lepton identification performance at the CEPC, including the impact of calorimeter reconstruction defects.

Findings

Lepton identification efficiency is about 98% for energies above 2 GeV.

Mis-identification rate is approximately 1% at the same energy threshold.

Performance degradation is mainly due to calorimeter reconstruction issues.

Abstract

Identifying the leptons inside jets is critical for the measurements of Higgs boson and the flavor physics program at the CEPC, a proposed Higgs/Z factory with the main ring circumference of 100 km. Using the CEPC baseline software, we analyze the identification performance of leptons generated inside a jet. The jet leptons are identified with typical efficiency and mis-identification rate of 98% and 1% for energy higher than 2 GeV, with the $Z\to bb$ process at 91.2 GeV center-of mass energy. At the benchmark channel of the CEPC flavor program of $B_{c}\to \tau\nu$ with $\tau \to e\nu\nu$, the electrons are identified with inclusive efficiency times purity of 97%, providing sufficient signal selection for the physics potential study. Compared to the single leptons, we found that these jet leptons identification efficiency degrades about 1-3%, and the mis-identification rate increases by less than 1% at the same working point. We analyze this effect and found that it is mainly caused by defects in the particle flow reconstruction code in the calorimeters. The dependence between the performance of the shower reconstruction and the lepton identification is quantified.