Study of K<SUB>s</SUB><SUP>o</SUP> Reconstruction and Lifetime Measurement at BESⅡ

WANG Zhe; YUAN Ye; ZHANG Chang-Chun

Chinese Physics C> 2003, Vol. 27> Issue(1) : 1-6

Study of K_s^o Reconstruction and Lifetime Measurement at BESⅡ

Institute of High Energy Physics, Chinese Academy of Science, Beijing 100039, China

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Abstract：
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^o 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 and the existence of the resonance of KⅡ0 , this channel is chosen to provide much pure K_s^o signal. With the aid of M. C. tools at BES Ⅱ , 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 Ks0 is measured with channel and the inclusive K_s^o mass is investigated with BES Ⅱ 's 50M J/ψ data sample, which give consistent Ks0 lifetime and mass with PDG' s value within error. 1C fit on K⁰_s mass is also studied with M. C. events. The resolution of momentum and energy of 7π+ , π- and K, is improved too.

References

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[2]	GUO Yun-Jun , HE Kang-Lin . Muon Identification Using the Efficiencies Ratio Method at BESⅡ. Chinese Physics C, 2007, 31(11): 1050-1055.
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[4]	LI Ming-Liang , ZHU Sheng-Jiang , CHE Xing-Lai , YU Ying-Nan . Research on Two-Quasiparticle Bands in ⁹⁸Sr. Chinese Physics C, 2004, 28(S1): 75-77.
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WANG Zhe, YUAN Ye and ZHANG Chang-Chun. Study of K_s^o Reconstruction and Lifetime Measurement at BESⅡ[J]. Chinese Physics C, 2003, 27(1): 1-6.

WANG Zhe, YUAN Ye and ZHANG Chang-Chun. Study of K_s^o Reconstruction and Lifetime Measurement at BESⅡ[J]. Chinese Physics C, 2003, 27(1): 1-6. shu

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Received: 2002-04-01
Revised: 1900-01-01

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沈阳化工大学材料科学与工程学院沈阳 110142

Study of K_s^o Reconstruction and Lifetime Measurement at BESⅡ

Corresponding author: WANG Zhe,

Institute of High Energy Physics, Chinese Academy of Science, Beijing 100039, China

Received Date: 2002-04-01
Accepted Date: 1900-01-01
Available Online: 2003-01-05

Abstract: 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^o 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 and the existence of the resonance of KⅡ0 , this channel is chosen to provide much pure K_s^o signal. With the aid of M. C. tools at BES Ⅱ , 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 Ks0 is measured with channel and the inclusive K_s^o mass is investigated with BES Ⅱ 's 50M J/ψ data sample, which give consistent Ks0 lifetime and mass with PDG' s value within error. 1C fit on K⁰_s mass is also studied with M. C. events. The resolution of momentum and energy of 7π+ , π- and K, is improved too.