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

摘要

Background Data Quality Monitoring system (DQM) was developed to monitor data quality at BESIII experiment in real time. The stable center-of-mass energy (E-cms) is essential for the data taking. Online monitoring the E-cms can help find the beam energy shift in time.Purpose The purpose is to monitor the E-cms in DQM system in real time.Methods The E-cms is measured using Bhabha scattering process in DQM system, due to its large cross section and low background level. The E-cms is calculated from the invariant mass of e(+)e(-), and the correction value from radiation effect and momentum calibration.Result The E-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.Conclusions The E-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.