用于$(K^{-},K^{+})$反应在线质子排斥的水$Č$ Erenkov探测器的研制
Development of Water $Č$erenkov Detector for On-line Proton Rejection in $Ξ^{-}$ Hypernuclear Spectroscopy via the $(K^{-},K^{+})$ Reaction
摘要：
计划使用新型磁谱仪Strangeness $-2$ Spectrometer（S-2 S）在J-PARC K1.8束线上进行$Ξ^{-}$超核与$(K^{-},K^{+})$反应的缺失质谱分析。设计了一个$Č$切伦科夫探测器，以折射率为1.33的纯水为辐射介质，用于S-2S中动量范围为1.2 ~ 1.6GeV/ $c$的质子在线抑制。原型水$Č$ erenkov探测器的开发和测试与正电子束和宇宙射线，以估计其质子排斥能力。我们用最新的宇宙射线原型实现了平均超过200个光电子，在一个月的预期光束时间内保持稳定。在宇宙射线测试中的原型的性能很好地再现与Monte Carlo模拟，其中一些输入参数进行了调整。基于Monte Carlo模拟，我们期望在整个S-2S接受过程中，在保持$>95\%$ $K^{+}$存活率的情况下，实现$>90\%$质子排斥效率。性能满足在J-PARC进行$Ξ^{-}$超核光谱研究的要求。
英文摘要：
The missing mass spectroscopy of $Ξ^{-}$ hypernuclei with the $(K^{-},K^{+})$ reaction is planned to be performed at the J-PARC K1.8 beam line by using a new magnetic spectrometer, Strangeness $-2$ Spectrometer (S-2S). A $Č$cerenkov detector with a radiation medium of pure water (refractive index of 1.33) is designed to be used for on-line proton rejection for a momentum range of 1.2 to 1.6 GeV/$c$ in S-2S. Prototype water $Č$erenkov detectors were developed and tested with positron beams and cosmic rays to estimate their proton-rejection capability. We achieved an average number of photoelectrons of greater than 200 with the latest prototype for cosmic rays, which was stable during an expected beam time of one month. The performance of the prototype in the cosmic-ray test was well reproduced with a Monte Carlo simulation in which some input parameters were adjusted. Based on the Monte Carlo simulation, we expect to achieve $>90\%$ proton-rejection efficiency while maintaining $>95\%$ $K^{+}$ survival ratio in the whole S-2S acceptance. The performance satisfies the requirements to conduct the spectroscopic study of $Ξ^{-}$ hypernuclei at J-PARC.
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