Research on the Software of Track Reconstruction in Vertex Chamber of BESII.pdfVIP

Research on the Software of Track Reconstruction in Vertex Chamber of BESII∗ ZENG Yu1) MAO Ze-Pu (Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100039, P.R.China) Abstract The software of track reconstruction of the vertex chamber of BESII-VCJULI was studied when it was transplanted from the HP-Unix platform to PC-Linux. The problems of distinct dictionary storage and precision treatment in these two different platforms were found and settled in the modified software. Then the obvious differences of the candidate track number in an event and some track parameters caused by them were reduced from 74% to 0.02% and from 5% to 0.5%, respectively. As a result, the quality of the track finding was greatly improved and the CPU time saved. Key words vertex chamber, track dictionary, track reconstruction, HP-Unix, PC-Linux 1 Introduction The Beijing Spectrometer II (BESII), which records information from electron positron interactions in the tau-charm energy region from 3-5GeV to study τ leptons, D mesons, J/ψ, and ψ’ physics, consists of several components [1]: the vertex chamber (VC), the main drift chamber (MDC), the time of flight counters (TOF), the shower counters (SC), muon counters (µC), luminosity monitor (LUM), solenoid magnet, electronics and its calibration system. The BESII vertex chamber consists of 640 aluminized Mylar drift tubes distributed in totally twelve layers. Except for the four middle stereo layers, which are used in Z directional track finding, the remaining eight layers are all axial ones used in track finding in r-φ plane. The whole twelve layers