ALICE实验内径迹系统探测器升级

大型重离子对撞实验(A Large heavy-Ion Collision Experiment，ALICE)按计划在大型强子对撞机(Large Hadron Collider，LHC)的第二次停机(2019—2021)期间进行探测器升级工作。为了对强相互作用物质——夸克胶子等离子体(Quark-Gluon Plasma，QGP)的性质进行更细致的研究，作为升级计划中重要的一个内容是把ALICE实验现有的内径迹系统探测器(Inner Tracking System，ITS)全面升级为基于单片有源像素传感器(Monolithic Active Pixel Sensor，MAPS)技术的硅像素探测器(习惯称之为ITS2)，并在Run 3和Run 4期间采集更多的铅核-铅核碰撞数据。新的ITS2共由7层(内3层，中间2层和外2层)探测桶面组成，共由24 000余片尺寸为3 cm × 1.5 cm的MAPS硅像素芯片(该芯片称之为ALPIDE)构成，有效探测面积达10 m2，共约120亿像素。ALPIDE芯片厚度为50 μm，单个像素的尺寸是27 μm × 29 μm，该芯片具有低功耗、高空间分辨率和高速读出等特点。ITS2将使ALICE探测器在测量极低横动量粒子时具备优异的探测效率和碰撞参数分辨率，同时也使ALICE探测器适应于LHC高束流亮度环境。目前ITS2的探测器模块量产和测试已于2019年完成，并在欧洲核子中心(CERN)洁净室完成了7层桶面的组装与安装，于2020年完成试运行测试。2021年1月启动ITS2在ALICE探测器中的安装与试运行工作，计划于2021年5月底完成ITS2的安装与测试。本工作将对ALICE/ITS2的探测器结构、ALPIDE芯片和升级进展等方面进行介绍。

Inner Tracking System Upgrade for the ALICE Experiment

A Large Ion Collider Experiment(ALICE) at the Large Hadron Collider(LHC) at CERN will undergo a major upgrade during the 2nd LHC Long Shutdown(LS2) scheduled in 2019~2021 that will allow to study in detail of strong interaction matter Quark-Gluon Plasma(QGP) properties. To collecting more Pb-Pb events during the Run 3 and Run 4, the replacement of the existing Inner Tracking System(ITS) with a completely new ultra-light high resolution detector based on Monolithic Active Pixel Sensors(MAPS) technique is one of the cornerstones within this upgrade program. The new ITS will consist of seven detection layers: 3 inner layers, 2 middle layers and 2 outer layers. The upgraded ITS will be realized using more than twenty-four thousand pixel chips (called ALPIDE) covering a total active surface of about ten square meters. The thickness of ALPIDE is 50 μm, also with a pixel pitch of 27 μm × 29 μm. The main features of the ALPIDE are of low power consumption, high resolution and high speed readout. ITS2 will enable the ALICE detector to have excellent detection efficiency and impact parameter resolution when measuring extremely low transverse momentum particles, and also make the ALICE detector suitable for LHC high luminosity environment. At present, the production and test of the detector module of ITS2 project have been completed, and the integration of 7-layer barrel been completed at CERN clean room, and the on-surface commissioning has been completed in the end of 2020. The installation plan of ITS2 at the ALICE detector has been started in Jan. 2021, and is scheduled to be finished in end of May 2021. This talk will focus on the design and the physics performance of the new ITS, as well as the advanced techniques adopted in detector assembly and integration will be introduced. The status and commissioning of the ITS upgrade project will be reported.