The Monte Carlo Simulation Of The BESIII Main Drift Chamber

The Beijing Spectrometer III (BESIII) operating at BEPCII is a new high precise detector built with modern detecting techniques. Its main physics goal is to study the eletroweak and strong interactions and to search for new physics at tau-charm energy region. Compared with its predecessor BESII, the better performance of BESIII needs more accurate detector simulation. The new BESIII Monte Carlo simulation software—BOOST(BESIII Object Oriented Simulation Tool) has been successfully developed.BOOST is an Object Oriented software package basing on Geant4 and C++,and uses some new software tools that are being widely used in high energy physics.BOOST simulates the full processes of the BESIII experiment, from event generation to raw data production.The Main Drift Chamber (MDC) is a kernel sub-detector in BES III. Its main function is to provide precise momentum measurement and dE/dx measurement for charged particles. The MDC is a columniform track detector, divided into inner barrel and outer barrel and consists of 43 sense wire layers including axial and stereo wire layers. MDC is designed to be a low-mass, small square cell drift chamber operated with helium-based gas, and the endcapes use special ladder-shape structure. Compare to the BESII drift chamber, the designed performance of the new BESIII drift chamber has improved a lot.The emphasis of this thesis is to develop the BESIII MDC simulation and test its performace. The MDC simulation is the important part of BOOST; The precise and reliable MDC simulation is meanful to finish the BESIII physics goal. More accurate and steady simulation is required for the new design of the BESIII Maid Drift Charmer, and the BOOST using object oriented technique development offers a more powerful and convenient program developing environment.To meet with the reqirement of higher performent, the BESIII MDC simulation uses more accurate method in geometry and matters description. The thesis introduces the MDC detector description, hits recording and digitization in the MDC simulation of BOOST. The way to structure the wire layers and cells and the new method to deal with the wires during the process of geometry and matters desriber are introduced in detail. With the MDC reconstruction, the tests of the MDC simulation performaces are done. The results of the tests show that the new MDC simulation performances are improved and close to the design goal, the speed and running stability of the MDC simulation can also meet the offline requirement.The result of simulation must close to the experiment at most. To march the key physical performace with the experiment, the result of MDC simulation has to compare with the experiment and tune all kinds of simulation parameters. It is great meanful to know the performace of simulation and how to do tuning by compare the controllable factors with the result of output and study the relationship between these factors and the simulation result and the relative among the factors.The parallel development of the BESIII offline system results the way of the MDC simulation, calibration and reconstructure to get geometry data are different.To avoid the conflict of geometry data, the I/O interface of the geometry data class of the MDC simulion and the MDC geometry service class are extended and the way to get geometry data is unified. In the pattern of BEPCII double-rings collation, the center of mass system moves away from the lab system.In order to closer and more convenient to compare with the experiment result, the final stat particle message which produced in the center of mass system has been boosted to the lab system by Lorentz Boost.