Research On Event Start Time Determination In BES By Using MDC Information

The Beijing Electron Positron Collider (BEPC) and Beijing Spectrometer (BES) in IHEP (Institute of High Energy Physics) of CAS (Chinese Academy of Sciences), as a national significant scientific and technological project, are under upgrade to satisfy the higher requirements from the physical analysis and the physical arm. This makes the offline data processing software system need re-designing and re-developing. The event reconstruction sub-system that is the important and core in the offline software system is one of important part of the physics analysis, and the event start time determination is the most important and first step in event reconstruction stage.This thesis gives a general introduction of particle physics and particle accelerators development, followed by the structure of BEPC, BES and its physical goal introduction briefly. The BES software development environment and the two methods of event start time determination are studied carefully. The first one is using information of the Time Of Flight counter (TOF) and the information of the tracks provided by the fast tracking code in main drift chamber (MDC). The second one is using the information of MDC time and information of the fast tracking. The differences between colliding events and cosmic ray events are tested carefully to design the algorithm. The C++ language and the OOP (Object Oriented Programming) are used to develop the algorithm, and the codes performance is tuned and checked by different Monte Carol (MC) data samples (single electron and hadron events). The results show that the algorithm is reasonable and reliable, meanwhile, the deficiencies of the algorithms are presented also. After studied the characteristics of some events whose start time can't be calculated by this two methods, according to the relationship between MDC geometric structure and event information, a new algorithm of event start time determination is developed with C++ language and OOP. This new algorithm is tested and checked carefully by the MC data samples, and the final results indicate that the new algorithm accord with the design requirements completely, which means that the efficiency and the precision of the algorithm satisfy the design aim.