Online monitoring of the center-of-mass energy from real data at BESIII
J. D. Lu, Yanjia Xiao, X. B. Ji
Abstract
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 ( $$E_\mathrm{cms}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>cms</mml:mi> </mml:msub> </mml:math> ) is essential for the data taking. Online monitoring the $$E_\mathrm{cms}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>cms</mml:mi> </mml:msub> </mml:math> can help find the beam energy shift in time. Purpose The purpose is to monitor the $$E_\mathrm{cms}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>cms</mml:mi> </mml:msub> </mml:math> in DQM system in real time. Methods The $$E_\mathrm{cms}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>cms</mml:mi> </mml:msub> </mml:math> is measured using Bhabha scattering process in DQM system, due to its large cross section and low background level. The $$E_\mathrm{cms}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>cms</mml:mi> </mml:msub> </mml:math> is calculated from the invariant mass of $$e^{+}e^{-}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>+</mml:mo> </mml:msup> <mml:msup> <mml:mi>e</mml:mi> <mml:mo>-</mml:mo> </mml:msup> </mml:mrow> </mml:math> , and the correction value from radiation effect and momentum calibration. Result The $$E_\mathrm{cms}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>cms</mml:mi> </mml:msub> </mml:math> 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 $$^2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msup> </mml:math> from signal extraction and 2.54 MeV/c $$^2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msup> </mml:math> from calibration and radiation correction. Conclusions The $$E_\mathrm{cms}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>cms</mml:mi> </mml:msub> </mml:math> 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.