Online monitoring of the center-of-mass energy from real data at BESIII
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ORIGINAL PAPER
Online monitoring of the center-of-mass energy from real data at BESIII Jiada Lu1,2
· Yanjia Xiao1,2 · Xiaobin Ji1,2
Received: 16 April 2020 / Revised: 1 June 2020 / Accepted: 27 June 2020 © The Author(s) 2020
Abstract 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/c2 from signal extraction and 2.54 MeV/c2 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. Keywords DQM · Center-of-mass energy · Bhabha process
Introduction BESIII experiment is operating at the Beijing Electron Positron Collider (BEPCII) in the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences, Beijing. With the peak luminosity of 1×1033 cm−2 s−1 , BESIII experiment has collected many the world’s largest samples of e+ e− collision data at different energy points in the τ -charm energy region [1].
Funding was provided by National Natural Science Foundation of China (NSFC) under Contracts Nos. 11775245, 11275210, U1832204.
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Jiada Lu [email protected] Yanjia Xiao [email protected] Xiaobin Ji [email protected]
1
Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
The BESIII detector is a magnetic spectrometer [2] located at the Beijing Electron Positron Collider (BEPCII) [3]. The cylindrical core of the BESIII detector consists of a heliumbased multilayer drift chamber (MDC), a plastic scintillator time-of-flight system (TOF), and a CsI(Tl) electromagnetic calorimeter (EMC), which are all enclosed in a superconducting solenoidal magnet providing a 1.0 T magnetic field. The solenoid is supported by an octagonal flux-return yoke with resistive plate counter muon identifier modules interleaved with steel. The acceptance of charged particles and photons is 93% over 4π solid angle. The charged-particle momentum resolution at 1 GeV/c is 0.5%, and the dE/dx resolution is 6% for the electrons from Bhabha scattering. The EMC measures photon energies with a resolution of 2.5% (5%) at 1 GeV in the barrel (end cap) region. The time resolution of the TOF barrel part is 68 p
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