研究CMS高粒度量能器之原型於CERN SPS測試粒子束下的表現

Abstract

世界上最大且能量最高的粒子加速器–大型強子對撞機(LHC)，正邁向「高亮度」(high luminosity)的運行階段，在下個階段，LHC會產生現階段10倍的累積亮度(integrated luminosity)，這會使偵測器面臨兩個重大的挑戰：輻射損傷(尤其是偵測器前緣)以及源於碰撞點產生的事件數上升使得單一事件的分析變得困難。 高粒度量能器(HGCAL)是緊湊秒子線圈實驗(CMS)的其中一項升級計畫，HGCAL將會取代現有的量能器兩端，包含電磁量能器與強子量能器的部分。其中電磁量能器與一大部分強子量能器會採用0.5到1平方公分大小的矽感應器，而其他部分則會以小的閃爍體探測器並運用矽光電倍增器做讀出，其中矽感應器精確的時間量測能幫助分辨短時間內產生的大量事件。 在2016年，以現存CALICE實驗開發的Skiroc2前端積體電路製程的第一個六角形矽偵測模組(module)已投入測試，而新的前端積體電路–Skiroc2cms也在2017及2018年投入測試。 本篇論文會以2016的測試粒子資料為主體進行2項研究，第一項是電子能量的回推(重建)，有兩種方法會被運用並比較；第二項研究則是運用射叢粒子(particle shower)在偵測器內的型態所定義的變數分辨電子與π介子。 本篇將詳細說明2016年所進行的粒子測試以及其實驗裝置、訊號重建與蒙地卡羅(Monte carlo)模擬的方法，而2017/2018年所進行的粒子測試之資料重建方法也將被大略提及。

The world's largest and most powerful particle accelerator, Large Hadron Collider(LHC), is proceeding to the High Luminosity phase. LHC will deliver 10 times more integrated luminosity than now. It will lead to significant challenges for radiation damage and event pileup on detectors, especially in the endcap part of the detector. High-Granularity Calorimeter(HGCAL) is the chosen technology by the Compact Muon Solenoid(CMS) experiment as part of the phase 2 upgrading program. Consisting of the electron-magnetic and hadronic sections, HGCAL will replace the existing endcap calorimeters.

The electromagnetic section and a large fraction of the hadronic section will be based on hexagonal silicon sensors of 0.5–1 $cm^{2}$ cell size, while the rest of the hadronic section will use small scintillator with silicon photomultiplier(SiPM) readout. The high-precision in timing capabilities of silicon will be helpful to pileup rejection.

First hexagonal silicon modules using the existing Skiroc2 front-end ASIC developed for CALICE has been tested in 2016. New front-end ASIC named Skiroc2cms is tested in 2017 and 2018.

This thesis will provide 2 studies based on one of the beam test data in 2016. The first study is the energy calibration of the electron. Two different methods will be explained and compared. The second study is the electron pion separation by the shower-shape variable. The test beam setup, data reconstruction and Monte Carlo generation of the 2016 test beam will be mentioned.

Furthermore, the studies of the data reconstruction in 2017/2018 beam tests will be briefly explained.