Dong Liu

For high-energy ${\pi }^0$ mesons, the angle between the two final-state photons decreases with the increase in the energy of the ${\pi }^0$, which enhances the probability of overlapping electromagnetic showers. The performance of the cluster splitting algorithm in the EMC reconstruction is crucial for the mass resolution measurement of ${\pi }^0$ with high energy. The cluster splitting algorithm is based on the theoretical lateral distribution of the electromagnetic showers. A simple implementation of the lateral distribution can be described as a (multi-)exponential function. In a realistic electromagnetic calorimeter, considering the granularity of the detector, the measured energy in a cell is actually the integral of the theoretical energy deposition, which deviates from the exponential function. Based on the simulation of the barrel EMC in the $\overline{\mathrm{P}}$ANDA experiment, a cluster splitting algorithm with a new lateral energy development function is developed. The energy resolution of overlapping showers with high energy has been improved.

Beijing Spectrometer (BESIII) is the leading experiment in operation in the field of \(c{\kern 1pt} - {\kern 1pt} \tau \) physics, which provides opportunity to study QCD properties in the transition region between non-perturbative and perturbative aspects. Here some of the QCD related studies are presented, including electromagnetic form factor of baryons, properties of the \(\phi (2170)\), and the anomalous magnetic moment of muon.

Electromagnetic form factors (EMFFs) are fundamental observable of baryons that intimately related to their internal structure and dynamics, where the EMFFs of hyperons provide valuable insight into the behavior of the strangeness. The EMFFs of hyperons can also help to understand those of nucleons as they are connected with the flavor SU(3) symmetry. The EMFFs of nucleons can be measured in both spacelike and timelike regions. However, it is difficult to probe the EMFFs of hyperons in spacelike region due to the unstable nature of hyperons. By means of electron-positron annihilation, the EMFFs of hyperons in timelike region is accessible via the production of hyperon-antihyperon pair. The timelike EMFFs of the isospin triplet $\Sigma$ hyperons measured at Babar, CLEO-c and BESIII experiments are reviewed in this paper. Besides, the relevant theoretical discussion based on the experimental results are also presented.

The cross section of the process $e^{+}{e}^{-}\to K^{+}{K}^{-}$ is measured at a number of center-of-mass energies $\sqrt{s}$ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of $M=2239.2\pm 7.1\pm 11.3\mathrm{MeV}/c^2$ and a width of $\mathrm{\Gamma }=139.8\pm 12.3\pm 20.6\mathrm{MeV}$, where the first uncertainties are statistical and the second ones are systematic. In addition, the timelike electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.