桶状抽样型电磁量能器(Electromagnetic Calorimeter,Ecal)是俄罗斯在建的重离子超导同步加速器(Nuclotron-based Ion Collider facility,NICA)中多功能探测谱仪(Multi-Purpose Detector,MPD)上的一个重要探测器,主要用于探测10 MeV至几个GeV能域内电子和光子的能量、时间、位置信息.基于Geant4软件,使用单能电子研究了入射位置及闪烁体层数对探测器模块(module)能量分辨率的影响,闪烁体层数和电子能量对探测器单元(tower)时间分辨率和Ecal位置分辨率的影响.模拟结果表明:随着电子入射位置由module边缘向中心移动,闪烁体内能量沉积由718 MeV增加至758 MeV;在tower长度为415.5 mm条件下,随着闪烁体层数增加,module能量分辨率变差,tower时间分辨率变好,Ecal位置分辨率变差.在兼顾量能器的各项性能后,tower中闪烁体最佳层数为211层,Ecal能量分辨率好于4.35%,时间分辨率小于112 ps,位置分辨率好于2 mm;在相同条件下,电子能量越高电磁量能器的时间分辨率和位置分辨率越好.
[Background]The barrel-sampled electromagnetic calorimeter(Ecal)is an important part of the Multi-Purpose Detector(MPD)in Nuclotron-based Ion Collider fAcility(NICA)that is being built in Russia.It is primarily used to detect energy,time,and position information of electrons and photons in the energy domain from 10 MeV to a few GeV.MPD-Ecal is comprised of 2 400 modules with 16 towers per module.Each tower is made up of alternating layers of 211 scintillator sheets and 210 lead sheets,as well as 16 wave-length shift fibers.[Purpose]This study aims to evaluate the performance,such as energy resolution,time resolution,and coordinate resolution,etc.,of the Ecal by simulation.[Methods]The Geant4 software was employed to simulate single-energy electron incident on Ecal to examine the effects of several parameters on the performance of Ecal.Influences of the position of the particle incidence point,the number and thickness of the scintillator and lead layers,the polish of the optical fibre end-face,and the energy and type of incident particles on the energy deposition and resolution,time distribution and time resolution,and coordinate resolution were investigated in details.Finally,the time resolution of a single tower was simulated using the natural cosmic ray package,and the tower's expected time resolution in the cosmic ray test was obtained.[Results]As the electron incidence position moves from the edge to the center of the module,the energy deposition within the scintillator rises from 718 MeV to 758 MeV.With a limited tower length of 415.5 mm,increasing the number of scintillator layers decreases the energy resolution of the module,improves the time resolution of the tower,and worsens the coordinate resolution of the Ecal.Taking into account the performance of the Ecal gauge,the optimal number of scintillator layers in the tower is 211.SiPM detects 42%more photoelectrons at a polish of 0.6 when the fiber end is coated with a reflective material than when it is not.As the polish of the fiber end-face increases,so does the number of photoelectrons detected by the SiPM,and the time resolution of the tower improves.When the fibre end-face polish is 1.0,the time resolution of the tower is less than 103 ps while time resolution of the tower(with 211 layers)in the cosmic ray is 185 ps.[Conclusions]The time and coordinate resolutions of Ecal improve with increasing electron energy under the same circumstances.