Simulation Study Of The Upgrade Of BESIII Endcap TOF

The Beijing Electron Positron Collider(BEPCII)is a double-ring high-luminosity multi-bunch electron-position collider operating in the T-charm energy region[1].The Beijing Spectrometer(BESIII)is a large-acceptance magnetic spectrometer located at BEPCll's beam interaction point[2].The BESIII experiment is of great significance in many physics subjects such as the measurement of ?-lepton,Charmonium,D meson correlation and light hadron spectrum,which play an important role in the precision examination of the standard model and the search for new physics[2,3].The time-of-flight detector(TOF)is one of the important sub-systems of BESIII.It is consisted with two parts:barrel TOF(BTOF)and endcap TOF(ETOF).Its main function is to identify charged particles by measuring the fl ight time[4].The particle identification(PID)ability depends on the precision of TOF time resolution,which is important for various physics topics of BESIII.BESIII off-line calibration results shows that the time resolution of ETOF,which is based on plastic scintillator technology,is significantly worse than that of barrel TOF employing the same technology[5].The new physics program of BESIII requires an upgraded ETOF of improved time resolution and PID ability.Simulation studies can help understand and evaluate some important problems in the upgrade of ETOF,including:what are the possible sources affecting the performance of ETOF,what type of timing detector is suitable for the upgrade,to what extent can the upgraded ETOF minimize the bad eff ects on time resolution,whether the expected performance of the upgraded ETOF can meet the PID requirements for the following BE SIII physics programs.In order to answer the above questions,the following research work has been completed in this thesis:(1)The main sources that affecting the timing performance are the materials of the sub-detectors inside the ETOF.In this study,we carefully analyzed the geometric structure and material composition of these sub-detectors,and setup a detector system containing the ETOF and the inside sub-detectors based on GEANT4 to simulate interactions between primary particles and these materials.The simulation results indicate that the secondary particles produced from the multi-scattering process have a bad influence on the timing performance of scintillator-based ETOF.(2)By replacing the plastic scintillator technique with the multi-gap resistive plate chamber(MRPC),it is found that the upgraded ETOF can utilize the small cell structure of MRPC-based ETOF and its insensitivity to photons,thus significantly reduce the probability of multiple hit.It is predicted that the timing performance of the upgraded MRPC-based ETOF is much better than that of the plastic scintillation-based one,which can meet the PID requirements of the BESIII physics topics.