The CERN Research Board approved the ATLAS Experiment's High Granularity Timing Detector (HGTD) project as part of the High-Luminosity Large Hadron Collider (HL-LHC) Phase-II upgrade on Sept. 16. This marks the official start of the HGTD project’s construction phase.

In the high-luminosity collision environment at the HL-LHC, the large increase in simultaneous interactions, known as pileup, will become a key experimental challenge. To counter this problem, ATLAS proposed developing the HGTD, which will use high precision time information to distinguish collisions at close distance in space. The HGTD detector covers the forward region of the ATLAS detector more comprehensively, thus improving detector physics performance in this region. The key to the HGTD detector is an innovative silicon sensor technology called Low-Gain Avalanche Detector (LGAD), which can provide ultra-high time resolution and moderate spatial resolution with high radiation resistance. Based on LGAD technology, the HGTD detector can achieve a time resolution of 30-50 picoseconds, which is a hundred times better than that of standard silicon detectors. The high-precision timing information improves the pileup reduction to improve forward object reconstruction and helps solve key scientific problems such as Higgs Boson precision measurements at the high-luminosity LHC.

The project will develop cutting-edge innovative technologies such as the ultra-fast sensor chip, ultra-fast readout chip and large-area fast detector assembly, which have attracted the interest of China, France, the U.S., Spain, Germany and other countries. Domestic institutes participating in the project are the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences, the University of Science and Technology of China (USTC), Nanjing University and Shanghai Jiaotong University.

The IHEP team has spearheaded the HGTD project in China and has played a leading role in the project. It has made important contributions to LGAD sensor R&D, detector module research, ASIC electronics, the DAQ system, and mechanics structure design, etc. For example, the IHEP team made the first hybrid ASIC and sensor mini-modules that proved the viability of HGTD technology in a test beam environment. Prof. Joao Guimaraes da Costa, Prof. Zhijun Liang and Prof. Jie Zhang proposed an innovative design for the hybrid ASIC and sensor modules to allow for more robust units and faster construction with less manpower. In addition to the above work, Prof. Jie Zhang also proposed an innovative and integrated solution for the flex cables and peripheral electronics in order to allow the detector to fit within its envelope. Prof. Zhijun Liang and Professors Mei Zhao and Prof. Xin Shi designed and cooperated with Chinese manufacturers to develop new LGAD sensors. In addition, they helped test and verify LGAD sensors developed by other manufacturers.^[1] This exciting project has attracted a young vibrant team including, so far, 14 PhD students and 5 postdocs.

Given the short time frame for detector construction, strict management organization is especially important. Prof. Guimaraes da Costa and Prof. Zhaoru Zhang led efforts to define related tasks; plan and schedule construction; calculate detector costs; and evaluate risk. The materials used in this process were reviewed by the Research Board and now will be the basis for the project’s next steps, including signing the Memorandum of Understanding (MoU).

The IHEP team holds key positions in the HGTD project. For example, Prof. Guimarães da Costa serves as the deputy Project Leader and Resources Coordinator. Prof. Zhijun Liang is convenor for the project's Module and Detector Units Development Group, which, in addition to R&D, is responsible for devising the module and detector unit construction plan that will be adopted by all HGTD institutes. Dr. Juan Garcia serves as convenor of the project’s Trigger and Data Acquisition System Group. Prof. Jie Zhang is convenor for the design of the HGTD peripheral circuit board.

The contributions of the HGTD team have been widely recognized. Prof. Karl Jakobs, spokesperson for the ATLAS Collaboration, noted that approval of the HGTD project is an "important milestone" for the ATLAS Collaboration. "We are happy about the strong IHEP participation, which is crucial for a successful realization of this challenging high-technology project," he said.

Prof. Yifang Wang, director of IHEP, said he was "really glad" about the HGTD approval and IHEP's role in it. He also emphasized that IHEP will "fully support the team" in completing the task.

Prof. Xinchou Lou, IHEP lead scientist for LHC, described how IHEP's Experimental Physics Division has done extensive work over the last 10 years to develop the silicon track detector and ASIC-dedicated electronics. He said the division has also put a lot of effort into developing laboratory resources and a talented research team. He noted that all of this work has made it possible for IHEP to make "significant contributions" to the design and verification of the ATLAS HGTD project and for numerous IHEP colleagues to win crucial management positions within the project.

Prof. Guimaraes da Costa, Leader of the IHEP ATLAS Group and the IHEP HGTD project, noted that the new LGAD technology deployed by the HGTD project makes it "one of the most exciting and innovative research projects in recent years." He said IHEP's young, multiskilled staff and infrastructure put the institute in an "ideal position to lead the research that will make the HGTD a reality."

Prof. Zhijun Liang, who is also IHEP team leader for a National Natural Science Foundation of China (NSFC) project related to the ATLAS detector upgrade, expressed his appreciation to the "young team" at IHEP for successfully developing and assembling the first batch of ATLAS HGTD detector mini-modules, which are notable for their excellent time resolution. Prof. Zhijun Liang said the ATLAS China team will play a key role over the next few years in international cooperative R&D on large-area detector modules, high time resolution sensors, ultra-fast ASIC readout chips and peripheral electronics, with the support of NSFC.

In addition to IHEP, other domestic institutes have made important contributions to the HGTD project. For example, USTC made contributions on LGAD sensor design and testing, and Prof. Yusheng Wu serves as the Physics and Performance Group coordinator for the HGTD project. A team from Nanjing University is also involved in peripheral circuit boards and readout electronics research.

This project is supported by the National Natural Science Foundation of China and the State Key Laboratory of Particle Detection and Electronics, China. Through the HGTD project, the IHEP team will promote the development of domestic ultra-fast detectors, laying the groundwork for the next generation of time-of-flight silicon detectors in partial physics experiments. In the meantime, the advanced technologies involved in the HGTD project will be widely used in other research fields, including positron emission tomography, proton CT medical imaging applications, and fast time measurement in astrophysics.

Note:

[1] The IHEP team has also made significant contributions to other aspects of the HGTD project. Prof. Jinyu Fu is responsible for the design of the mechanical structure of the HGTD outer ring. Prof. Mingyi Dong is responsible for flexible circuit board testing in the HGTD module. Prof. Xuai Zhuang and Prof. Yanping Huang made important contributions to the beam testing of the HGTD.