Improvements Of Position Reconstruction And Correction For The Calorimeter At Besiii

The Electromagnetic Calorimeter (EMC) is one of the important components of the Beijing Spectrometer(BESⅢ), its basic function is measuring the shower position and shower energy for electrons and neutral particles. Precise measurement of particles shower position has an important effect on the reconstruction of π0and η, daughter particles reconstruction and position precision has a significant effect on the BESⅢ physics analysis, so EMC must have the very good position resolution. Due to interactions with matter and bias from position reconstruction algorithm. For the high position resolution, position reconstruction algorithm and correction parameters should be studied to correction EMC reconstruction positions to the expected positions. The studying and improvement in this thesis are based on the original position reconstruction and position correction method, more reasonable position correction parameters are given in this paper, positioning accuracy and position reconstruction performance of EMC are improved after position correction.Position correction include polar angle and azimuth, simple position correction parameters had been set using Monte-Carlo(MC) samples and position correction parameters for real data been set in polar angle, position reconstruction software had used the position correction parameters for BESIII physics analysis. Position correction are further studied in this thesis base on this position reconstruction software, for the new MC samples position correction parameters, azimuthal correction parameters take into account the dependence of energy and polar angle for EMC barrel, for EMC endcaps, position correction parameters are set for each layer and taken into account the dependence of shower energy in polar angle and azimuth. For real data, the small difference from MC data are found by qualitative analysis and corrected by using Bhabha events.After position correction, the performance of the position reconstruction is given by Bhabha events、radiation Bhabha events、digamma events and the process J/ψ/�'ρπ for real data and MC data, the results show that the offsets of position reconstruction are close to zero, the position resolution are improved and the results of real data and MC data are basically consistent, at the same time, electron position resolution at1GeV is about5.6mm which reaches its designed goal.