Developments of Tracking Methods of Muon Pairs with SeaQuest Spectrometer
Developments of Tracking Methods of Muon Pairs with SeaQuest Spectrometer
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SeaQuest光谱仪μ子对跟踪方法的进展
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发表时间：
2014
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通讯作者：
F. Sanftl
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作者：
ﾌﾛﾘｱﾝ ｻﾞﾝﾌﾄｭﾙ;F. Sanftl
SeaQuest实验是一个位于费米国家加速器实验室（Fermi Nation Accelerator Laboratory）的固定目标实验。它从120 GeV束流（√ s= 11 GeV）引起的质子质子碰撞中检测Drell-Yan μ子对。本文提出了一种新的方法，该方法允许在SeaQuest实验的第一次调试运行期间记录的高多重数数据中的双μ子的径迹重建。SeaQuest光谱仪是一种前向光谱仪，通过聚焦磁体进行优化，对高pT μ子对特别敏感。在聚焦磁铁内部放置一个大铁块来阻挡强子背景。四个跟踪站用于轨道重建。前三个台站由漂移室组成，第四个台站由漂移管组成。每个跟踪站中的描迹器阵列触发双μ子事件。一个单独的分析磁铁测量μ子的动量。Drell-Yan过程发生在高能强子碰撞中，当一个强子的夸克和另一个强子的反夸克湮灭时，产生一个虚光子，然后衰变成一对带相反电荷的μ子。双μ子的运动学与质子中的反夸克直接相关。2012年春天，第一束120 GeV质子束成功地从费米实验室主注入器环提取到SeaQuest的固定靶束线。在6周的试运行期间，质子的平均强度为每次溢出7× 1011。本论文报告了基于调试运行数据的双μ子径迹重建分析方法的发展。SeaQuest的轨道重建由两个步骤组成：“寻轨”，将不同漂移室中的撞击结合到轨道候选者中，以及“轨道拟合”，根据谱仪的已知磁场图确定μ子轨道的动量。在调试运行过程中，传输光束的占空因数不稳定，导致了较大的多重性。每个跟踪站每次事件的漂移室平均占有率在30%~ 60%之间。为了处理这些高占用率，开发了一种创新的航迹查找算法。它能够在前三个跟踪站中快速关联双μ子命中，并以98%以上的效率构建轨道候选者。通过只考虑漂移室命中，可以将漂移室占用率降低到10%，其中漂移室命中可以成功地与μ子轨道候选者相关联。该算法显着提高了重建的双μ子的绝对产量。IV
The SeaQuest experiment is a fixed-target experiment located at Fermi Nation Accelerator Laboratory (Fermilab). It detects Drell-Yan muon pairs from protonproton collisions induced by a 120GeV beam ( √ s= 11GeV). A new method which allows the track reconstruction of dimuons in high multiplicity data recorded during the first commissioning run at the SeaQuest experiment is presented in this thesis. The SeaQuest spectrometer is a forward spectrometer optimized by a focusing magnet to be particularly sensitive to high-pT muon pairs. A large iron block is placed inside the focusing magnet to stop hadronic background. Four tracking stations are used for track reconstruction. The first three stations consist of drift chambers, and the fourth station consists of drift tubes. Hodoscope arrays in each tracking station trigger dimuon events. A separate analyzing magnet measures the momenta of muons. The Drell-Yan process occurs in high-energetic hadron collisions when a quark of one hadron and an antiquark of another hadron annihilate, creating a virtual photon, which then decays into a pair of oppositely charged muons. The dimuon kinematics are directly related to the antiquarks in the proton. In spring 2012, the first 120GeV proton beam was successfully extracted from the Fermilab Main Injector Ring to the fixed target beamline of SeaQuest. The average intensity of the protons during the 6 weeks of commissioning run was 7× 1011 per spill. This thesis reports developments of analysis methods for the dimuon track reconstruction based on data from the commissioning run. The track reconstruction at SeaQuest consists of two steps: the ’track finding’ which combines hits in the different drift chambers to a track candidate, and the ’track fitting’ which determines the momentum of a muon track based on the known map of the magnetic field of the spectrometer. The duty factor of the delivered beam during the commissioning run was unstable and it caused large multiplicities. The average occupancies of the drift chambers were between 30% and 60% in each tracking station per event. In order to deal with these high occupancies, an innovative track finder algorithm was developed. It is capable of quickly correlating dimuon hits in the first three tracking stations and building track candidates with an efficiency above 98%. The drift chamber occupancies could be reduced to 10% by only considering drift chamber hits which can successfully be associated to muon track candidates. The algorithm significantly improved the absolute yield of reconstructed dimuons. IV