The Calibration Of BESIII TOF System

The upgraded BEPCII/BESIII is a unique and powerful facility for studying inτ-Charm energy region, with a research program that covers charmonium physics, D-physics, spectroscopy of light hadrons andτ-physics. It will also play an importantrole towards our understanding of the Standard Model and enable search for possiblenew interactions. Time of Flight (TOF) counters as one of its sub-detector is mainlyused to measure the time of ?ight of charged particles for particle identification(PID).Its capability of PID is determined by the time resolution which can be improved bycalibration.This thesis focuses on the of?ine calibration of TOF which including time of flightcalibration,attenuation length of scintillator,Q0 calibration and effective the velocitycalibration.Learn from the experience of BELLE and BESII and consider with the actual sit-uation of BESIII, we structure the empirical formula for the calibration of TOF. Theelectronic scan curve of each electronics channel is obtained to correct measured pulseheight values which are beyond the dynamic range. The Kalman filter method is em-ployed to calculate the predicted time step by step, instead of taking the track trajectoryas a standard helix. For the barrel TOF, weighted time of double-end and double-layerare presented respectively.For the end cap TOF, the material interactions of electrons in bhabha events wouldgenerate showers as fake signals recorded by TOF electronics, which causes the worsetime resolution(～150ps) compared with muons(～110ps). The preliminary performancecheck of hadron samples shows the similar pulse height distribution with electrons andthe electrons are easier to satisfy the statistic requirement for frequent calibration be-cause of the high cross section, so we choose bhabha events for the end cap calibration.For the barrel TOF, the difference of time resolution of electrons and mouns is small.Because the time resolution is heavily related to the uncertainty from bunch length andbunch time, the difference of time resolution during data taking has been discussed inthis thesis. The capability of K/πseparation of TOF is also described in this thesis.The calibration results of attenuation length of scintillator,Q0 and effective ve-locity are presented and we check the change of the attenuation length as time gose.Neutral particle has no tracks in MDC but possibly causes signal in TOF and the hit position could be extracted by effective velocity.