BESIII μ子计数器磁场的校准和测量
Alignment and measurement of the magnetic field for the BESIII muon counter
摘要：
根据2012年夏季BEPCII关闭期间用BESIII探测器拍摄的无磁场的宇宙射线事件和2009年在质心能量为3.686 GeV时采集的数据样本中的双μ子事件，我们将BESIII μ子计数器中记录的命中坐标与预期的相互作用点进行了比较，所述预期的相互作用点是在没有一个磁场通过最小化的差异，我们对准μ子计数器与内部跟踪系统。此外，在μ子计数器的磁场的强度进行了测量的第一次与双μ子事件从数据采取的质心能量为3.686 GeV。在对准和磁场强度测量之后，μ子径迹的重建命中位置的偏移减小，这改善了μ子识别。BESIII最新版离线软件系统采用了准直和磁场强度测量两种方法。在使用μ子计数器信息的情况下，对软件的这种添加减少了物理分析的系统不确定性。
英文摘要：
Based on cosmic ray events without a magnetic field taken with the BESIII detector during the summer shutdown of BEPCII in 2012 and di-muon events from a data sample taken at center-of-mass energy of 3.686 GeV in 2009, we compare the coordinates of hits registered in the BESIII muon counter with the expected interaction point extrapolated from reconstructed tracks from the inner tracking system in the absence of a magnetic field. By minimizing the difference, we align the muon counter with the inner tracking system. Moreover, the strength of the magnetic field in the muon counter is measured for the first time with di-muon events from data taken at a center-of-mass energy of 3.686~GeV. After the alignment and the magnetic field strength measurement, the offsets in the reconstructed hit positions for muon tracks are reduced, which improves the muon identification. The alignment and magnetic field strength measurement have been adopted in the latest version of the BESIII offline software system. This addition to the software reduces the systematic uncertainty for the physics analysis in cases where the muon counter information is used.
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