Study of photon detection efficiency and position resolution of BESIII electromagnetic calorimeter

We study the photon detection efficiency and position resolution of the electromagnetic calorimeter (EMC) of the BESIII experiment. The control sample of the initial-state-radiation (ISR) process of $e^+e^-\rightarrow \gamma \mu^+\mu^-$ is used at $J/\psi$ and $\psi(3770)$ resonances for the EMC calibration and photon detection efficiency study. Photon detection efficiency is defined as the predicted photon, obtained by performing a kinematic fit with two muon tracks, matched with real photons in the EMC. The spatial resolution of the EMC is defined as the separation in polar ($\theta$) and azimuthal ($\phi$) angles between charged track and associated cluster centroid on the front face of the EMC crystals.Comment: 5 page

The expected measurement precision of the branching ratio of the Higgs decaying to the di-photon at the CEPC

This paper presents the prospects of measuring $\sigma(e^{+}e^{-}\to ZH)\times Br(H \to \gamma\gamma)$ in 3 $Z$ decay channels $Z \to q\bar{q} / \mu^{+} \mu^{-} / \nu\bar{\nu}$ using the baseline detector with $\sqrt{s} = 240 GeV$ at the Circular Electron Positron Collider (CEPC) . The simulated Monte Carlo events are generated and scaled to an integrated luminosity of 5.6 $ab^{-1}$ to mimic the data. Extrapolated results to 20 $ab^{-1}$ are also shown. The expected statistical precision of this measurement after combining 3 channels of $Z$ boson decay is 7.7\%. With some preliminary estimation on the systematical uncertainties, the total precision is 7.9\%. The performance of CEPC electro-magnetic calorimeter (ECAL) is studied by smearing the photon energy resolution in simulated events in $e^{+}e^{-} \to ZH \to q\bar{q}\gamma\gamma$ channel. In present ECAL design, the stochastic term in resolution plays the dominant role in the precision of Higgs measurements in $H \to \gamma\gamma$ channel. The impact of the resolution on the measured precision of $\sigma(ZH)\times Br(ZH \to q\bar{q}\gamma\gamma)$ as well as the optimization of ECAL constant term and stochastic term are studied for the further detector design

Fast simulation of the CEPC detector with Delphes

Fast simulation tools are highly appreciated in particle physics phenomenology studies, especially in the exploration of the physics potential of future experimental facilities. The Circular Electron Positron Collider is a proposed Higgs and Z factory that can precisely measure the Higgs boson properties and the electroweak precision observables. A fast-simulation toolkit dedicated to the CEPC detector has been developed using Delphes. The comparison shows that this fast simulation tool is highly consistent with the full simulation, on a set of benchmark distributions. Therefore, we recommend this fast simulation toolkit for CEPC phenomenological investigations

Probing Higgs CPCP properties at the CEPC

In the Circular Electron Positron Collider (CEPC), a measurement of the Higgs $CP$ mixing through $e^{+} e^{-} \rightarrow Z H \rightarrow \mu^{+} \mu^{-} H(\rightarrow b \bar{b} / c \bar{c} / g g)$ process is presented, with $5.6\ \mbox{ab}^{-1}$$e^{+} e^{-}$collision data at the center-of-mass energy of$240\ \mathrm{GeV}$. In this study, the$CP$-violating parameter$\hat{\alpha}_{A \tilde{Z}}$is constrained between the region of$ -8.27\times 10^{-2}$and$8.09 \times 10^{-2}$and$\hat{\alpha}_{Z \tilde{Z}}$between$-2.15 \times 10^{-2}$and$2.02 \times 10^{-2}$at$95\%$confidence level. This study demonstrates the great potential of probing Higgs$CP$ properties at the CEPC