Study of BESIII electromagnetic calorimeter performance with radiative lepton pair events

We study the photon detection efficiency and position resolution of the electromagnetic calorimeter (EMC) of the BESIII detector. The control samples of the initial-state-radiation (ISR) process of?e+e?→γμ+μ??at?J/ψ?and?ψ(3770)?resonances are used for the calibration of the photon cluster shapes and photon detection efficiency study. The photon detection efficiency is defined as the fraction of predicted photon, determined by performing a kinematic fit with the four momenta of two charged tracks only, matched with the actual photons in the EMC. The spatial resolution of the EMC is studied in polar (θ) and azimuthal (?) angle directions in a cylindrical coordinate system centered at the interaction point, with z-axis along the beam direction.