Study Of The Operating Performances And Noise Of MDC At BESIII

Beijing spectrometer III (BESIII) runs on the upgraded Beijing electron-positron collider II (BEPCII), is a large general magnetic spectrometer. The goals of BESIII experiment are the precision measurement and the search for new physical in Tau-Charm. Main Drift Chamber (MDC) is the innermost sub-detector of BESIII, which is also the center tracking detector. Its main task is to measure the track and the momentum and energy loss of the charged particles.The operating performance of MDC mainly includes spatial resolution, momentum resolution, hit efficiency. The paper shows a study on the performance of MDC with the online Bhabha events between December 2013 and May 2014, includes the variation of the spatial resolution and hit efficiency as a function of the layer, the influence of the incident angle on reconstructed momentum, as well as the influence of high voltage and the operating gas on MDC performance. To find the the potential problems of the detector, we checked the above performances run by run during the period of BESIII data taking.During the running of MDC, noise is inevitable.The noise is not only an important factor which affects the actual running performance of MDC,but also one of the important factors that affect the consistency of data and Monte Carlo.The paper introduces the resource of MDC noise,and gives the variation of noise with layers and time of data taking. We also studied a particular noise related to the clock in the T channel. In addition, this thesis summarizes the variation of MDC noise in the last six years since the data taking of BESIII in 2009. The noise related to beam background is highest in the inner chamber since it is closest to the beam pipe. Samples with different noise levels were selected to study the impacts of the noise on the hit efficiency and the spatial resolution.The results show that the higher the noise occupancy, the worse the spatial resolution and the hit efficiency.After six years of operating, MDC aging problem appears. Experimental analysis results show that MDC gain is decreasing year by year. In order to obtain the influence the aging of the signal wire on MDC performance, we must select the samples with same high pressure, gas and magnetic field as well as the similar noise level. Finally, the paper gives how the spatial resolution and the hit efficiency vary year by year. The results show that the first 3 layers of spatial resolution and hit efficiency are significantly worse year by year, the other layers’variation is not obvious.This study can not only help to understand the running status of MDC, but also provide necessary information for the tuning of MDC simulation, which is important to improve the consistency of data and MC. Moreover, the research of aging effect can provide an important reference for the upgrade of the inner chamber.