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Offline calibration plays an important role in BES offline data processing. In order to achieve good spatial and momentum resolution, it is necessary to implement high precision offline calibration for the BES drift chamber. This paper studies the time-to-distance relations, which are important calibration constants for track reconstruction. The parameterization of the time-to-distance relation, studies of left-right asymmetry and studies of variation with entrance angle are performed. The impact of dead channels on the time-to-distance relation is given special attention in order to reduce the shift in measured momentum for tracks passing near dead cells. Finally we present the resolutions for barrel Bhabha events(|cos θ|< 0.8) from a J/ψ data set taken in 2012. The average spatial resolution is 123 μm and the momentum resolution for 1.548 Ge V/c Bhabha tracks is 11.9 Me V/c. 相似文献
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王海霞 张玉虎 丁兵 周小红 张宁涛 柳敏良 马英君 Y. Sasakiz K. Yamada H. Ohshima S. Yokose M. Ishizuka T. Komatsubara K. Furuno 《中国物理快报》2010,27(8):58-61
High-spin states in the beam energies. A new and 72 γ transitions odd-odd nucleus ^128I are investigated via the ^124 Sn(^7 Li,3n)^128 I reaction at 28 and 32 Me V level scheme of 12sI is established up to high-spin states at I^π = 16, including 48 levels The present level scheme is largely different from the one in a recent publication due to identification of several doublet and triplet γ transitions and their proper placements in the level scheme. The high-spin level structure exhibits no obvious collective properties and is possibly associated with two and multi-quasiparticle configurations. 相似文献