The Offline Tuning For The BESⅢ Main Drift Chamber Simulation

The Beijing SpectrometerⅢ(BESIII) is a general-purpose detector working at the upgraded Beijing Electron-Positron ColliderⅡ(BEPCII). It is designed for detecting the various final states produced in e+e- collisions near center of mass energies of about 3～4GeV and it's physics goals are the precision measurement and the search for new physics inτ-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 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 BESIII. Its main function is to provide precise tracking position, momentum measurement and dE/dx measurement for charged particles. According to the design report of the BESIII detector,the single wire resolution is assumed to be 130μm for the BESIII drift chamber.the momentum resolution for 1 GeV/c charged particles should be around 0.5%, and the dE/dx resolution could be 6%～7%. The goal of the tuning software is to adjusting tuning parameters based on the experiment data and changing many tuning parameters in the simulation digitization process, to make performance of simulation data coincident with the experiment data after times iterative circulation.The emphasis of this thesis is to introduce the process of MDC simulation tuning. The thesis introduces the MDC detector geometry description, tuning software framework and tuning method, processes and result in the MDC simulation of BOOST. Under the BESIII Offline Softeare System (BOSS), we construct simulation tuning software framework include MdcParTuning algorithm package and MdcTuningSvc I/O service.Simulation tuning and physics analysis testing has been carried out based on using the real data taken in October 2009 to 2011. Our main sample is Bhabha events,π+π-J/φand dimu. Simulation tuning focus on the wire hit efficiency and spatial resolution which affect the response of detector. To wire hit efficiency tuning, we change it using the contrast between real data, the former tuning parameter and simulation data. To spatial resolution tuning, fitting residual of real data and simulation data, getting fitting parameters and changing the fitting parameters based on the different between real data fitting result and simulation data fitting result are our processes. Repeat the front process again and again until hit reconstruction efficiency and distribution of the real data is consistent well with the simulation data. We have achieved the hit reconstruction efficiency difference between real data and Monte Carlo data is less than 1%, greatly reduce the system error reached the goal of releasing article. The BESIII physics articles we have released and will release based on the work depicting in this thesis.