Wang, Z (reprint author), Chinese Acad Sci, Inst High Energy Phys, Beijing 100039, Peoples R China.
The beam collision center of the BEPC has slightly shifted from geometrical origin of the BES detector and the beam bunch of the BEPC also has certain size. For these reasons, to measure K-s(0) lifetime, primary vertex reconstruction must be carried out. After the investigation of di-muon bhabha and hadron events, the beam collision center for each run is determined by bhabha and di-muon events. For the large branching ratio of J/ -->K-s(0), K-*0-->K+/- pi(-/+): pi(+) pi(-) and the existence of the resonance of K (*0), this channel is chosen to provide much pure K-s(0) signal. With the aid of M. C. tools at BES U, existing software for secondary vertex reconstruction is adjusted and improved. A new method of secondary vertex determination is used and a better position resolution of secondary vertex is obtained. The lifetime of K-s(0) is measured with channel J/ -->K-s(0), K-*0 and the inclusive K-s(0) mass is investigated with BES parallel to 's 50M J/ data sample, which give consistent K-s(0) lifetime and mass with PDG's value within error. 1C fit on K-s(0) mass is also studied with M. C. events. The resolution of momentum and energy of pi(+) pi(-) and K-s(0) is improved too.