Online monitoring of the center-of-mass energy from real data at BESIII

Abstract

BackgroundData Quality Monitoring system (DQM) was developed to monitor data quality at BESIII experiment in real time. The stable center-of-mass energy (E_mathrm{cms}) is essential for the data taking. Online monitoring the E_mathrm{cms} can help find the beam energy shift in time.PurposeThe purpose is to monitor the E_mathrm{cms} in DQM system in real time.MethodsThe E_mathrm{cms} is measured using Bhabha scattering process in DQM system, due to its large cross section and low background level. The E_mathrm{cms} is calculated from the invariant mass of e^{+}e^{-}, and the correction value from radiation effect and momentum calibration.ResultThe E_mathrm{cms} calculated with DQM system shows a good consistency with that from offline reconstruction within error. The results are validated with data taken in 2013. The overall systematic uncertainty includes 0.39 MeV/c^2 from signal extraction and 2.54 MeV/c^2 from calibration and radiation correction.ConclusionsThe E_mathrm{cms} calculated from Bhabha scattering process is now available on DQM system in real time, which can be used as references for researchers to operate BESIII experiment.