Abstract
During the 2016-17 and 2018-19 running periods, the BESIII experiment collected 7.5 fb of collision data at center-of-mass energies ranging from 4.13 to 4.44 GeV. These data samples are primarily used for the study of excited charmonium and charmoniumlike states. By analyzing the di-muon process , we measure the center-of-mass energies of the data samples with a precision of 0.6 MeV. Through a run-by-run study, we find that the center-of-mass energies were stable throughout most of the data-collection period.
Highlights
The BESIII experiment [1] was designed to study physics in the τ-charm energy region (2.0 – 4.9 GeV) [2] through e+e− annihilations produced by the BEPCII storage ring [3]
Where Mp(μ+μ−) is the peak position of the μ+μ− invariant mass of selected di-muon events; ∆MISR/final state radiation (FSR) is the mass shift due to the emission of initial state radiation (ISR) or FSR photons, estimated from Monte Carlo (MC) simulation of the dimuon process by turning the ISR/FSR processes on and off in MC generation; and ∆Mcal is the correction introduced by the momentum calibration of the μ+μ− tracks, obtained from an analysis of the process e+e− → γISRJ/ψ
The cylindrical core of the detector covers 93% of the full solid angle and consists of a helium-based multilayer drift chamber (MDC), a plastic scintillator time-of-flight system (TOF), and a CsI(Tl) electromagnetic calorimeter (EMC), all of which are enclosed in a superconducting solenoidal magnet providing a 1.0 T magnetic field
Summary
The BESIII experiment [1] was designed to study physics in the τ-charm energy region (2.0 – 4.9 GeV) [2] through e+e− annihilations produced by the BEPCII storage ring [3]. An alternative algorithm was developed to measure the Ecm for data samples above 4 GeV This method uses the well-understood QED process e+e− → (γISR/FSR)μ+μ− (the di-muon process), where γISR/FSR is a radiative photon due to initial state radiation (ISR) and/or final state radiation (FSR). Using this method, a precision of 0.8 MeV was previously achieved for data from 2011 to 2014 [6]. Where Mp(μ+μ−) is the peak position of the μ+μ− invariant mass of selected di-muon events; ∆MISR/FSR is the mass shift due to the emission of ISR or FSR photons, estimated from Monte Carlo (MC) simulation of the dimuon process by turning the ISR/FSR processes on and off in MC generation; and ∆Mcal is the correction introduced by the momentum calibration of the μ+μ− tracks, obtained from an analysis of the process e+e− → γISRJ/ψ
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