Overview

　　The Super large Collider LHC（Larger Hadron Collider） being built at European Organization for Nuclear Research (CERN) is a proton-proton collider with the highest energy in the world. Two high energy physics experiments, ATLAS and CMS are located on its two colliding points with specific features respectively, to study the most advanced topics of high energy physics.

　　In the Greek mythology, titan ATLAS was one of the giants, who was punished to support the sky with his two hands for offending Olympian gods. It is expected, for LHC, that the ATLAS detector, undertaking tremendous task in physics research, will be the strongest one with titanic force and bring good luck to physicists.

　　The main physics goal of LHC is to explore the long expected Higgs mechanism, which is the key point of spontaneous symmetry breaking electro-weak standard model. ATLAS is a large general purpose detector with which the potential of proton-proton colliding of LHC would be explored sufficiently. The design scheme of ATLAS, proposed in November of 1992 weighs about 7000 tons, with an investment of 470 million Swiss Francs. There are two types of magnets: an inner solenoid magnet with 2 Tesla magnetic field strength surrounding the inner detector and a toroidal superconducting air core outer magnet located outside the calorimeters. Particle tracks are measured with the inner detector associated with the inner magnet, which is mounted in a cylinder with the diameter of 2.3 m and the length of 6.8 m. The outer magnet has the dimension of 26 m in length and 20 m in outer diameter. ATLAS detector is equipped with many new techniques, such as silicon pixel detector and micro-strip detector with very high spatial resolution, transition radiation straw tube detector, located a little farther from the beam pipe. This detector configuration guarantees the high level of the inner detector in respect of pattern recognition, momentum and vertex measurement and the improvement of electron identification. Muon spectrometer is located at the outermost layer of ATLAS, which is composed of muon particle detectors and a set of air core toroid magnets with a light open structure, providing very large magnetic space and bending ability and causing very low multiple-scattering.

　　The design of ATLAS detector is optimized to search Higgs particles in the most probable mass area. W-like particles and Z-like particles, coming from SUSY particles or from compositeness fundamental fermions, could also be searched. ATLAS detector also meets the requirement of studying CP violation in B decays and detailed study of Top quark. Owing to its extensive potential in physics research and the vitality in the next 20-30 years, ATLAS has attracted 1800 physicists from about 150 institutes and universities all over the world. The participants come from the member states of CERN, such as Germany, Great Britain, France, Italy, as well as from some other important countries, such as USA, Russia. Japan and China.

　　On 30th November of 1999, deputy chairman of National Natural Science Foundation of China (NNSFC) WANG Naiyan, research director of CERN, Professor R.Cashmore and the spokespersons from both sides signed the “Memorandum of Mutual Understanding between the Participant Member and CERN on ATLAS Collaboration”(MoU). From then on the Chinese ATLAS collaboration has started formally. According to MoU, the Chinese cluster, including the Institute of High Energy Physics (IHEP) and university cluster (Nanjing University, Shandong University, the University of Science and Technology of China (USTC)), will participate in the research and building of detectors and data analysis, and share physics results. The total budget of the task undertaken by the Chinese cluster is 5 million RMB.

Content of Collaboration

　　Chinese cluster, including IHEP group and university cluster (Nanjing University, Shandong University and USTC) undertake the task in the respects of muon spectrometer and hadronic liquid argon calorimeter.

　　The muon chamber system includes two kinds: one for precise track measurement and the other for trigger purpose. Monitored drift tube (MDT) chambers and cathode strip chambers are (CSC) used for precision measurement. Resistive plate chambers (RPC) and thin gap chambers (TGC) are for trigger purpose.

　　The group of IHEP undertakes independently the task of building BEE chamber system located in the transit region between the barrel and end-cap part of the muon spectrometer. BEE system consists of 32 MDT chambers. The procedure of MDT tube mass production is determined based on the prototype research and on the optimization of mature technologies, which are associated with domestic conditions, such as the selection of effective methods to test wire tension, wire location, dark current and gas leakage of the MDT. Then, in a clean (grade 10000) and temperature (20±1°C)-humidity control room, a production line for 6500 MDT tubes will be built. And in order to guarantee the quality of the tubes, a set of quality assurance and quality control (QA/QC) will be used. Furthermore, by using these MDT tubes, 34 BEE chambers (2 for spare) will be assembled only after chamber module-0 is inspected and passed by the MDT experts group from ATLAS. For the production and test of BEE chambers, many facilities are under preparation, such as the gas system, the precise mechanical location system and the cosmic ray test stand so as to assemble precisely and test their characteristics, such as efficiency, global spatial resolution, noise, etc.

　　The highest precision, the largest information capacity and the most complicated environment (high background with serious radiation influence) of the ATLAS experiment will inevitably lead to the most complicated event reconstruction and adoption of the newest calculating technologies. Thus, IHEP group also undertakes the tasks of associated database and software on a broad scale. The tasks include: the building of the BEE chamber database as part of the muon spectrometer of ATLAS according to the rule from the muon group, installing and exploring the simulation software of ATLAS detector; the setting up of the simulation and calculating environment at IHEP in order to study the performances of BEE and muon system and the selection of appropriate physics topics, accomplishing the physics simulation and data analysis.

　　In the first stage it needs to put appropriate manpower to pursue and grasp the advanced theory and the key points of the experiment in order to find out the physics target and to ensure the obtainment of independent physics results in a planned way.

　　The university cluster participates in the research and manufacture of hadronic liquid argon end-cap calorimeters and forward muon trigger electronics. Nanjing University, collaborating with Canadian group will finish the manufacture of copper absorbers (front and back wheels), provides 3 pieces out of 32 back absorbers and takes part in the beam test of the calorimeter at CERN, the stability test and the data analysis. The requirement of the flatness tolerance and high surface rating of copper absorbers with the length of 1658mm is very strict because of the very fine gap (l .8mm) between electrode plates. Besides, owing to the softness and thinness (1 2.5 cm), the copper absorbers will become deformed during transportation, mounting and storage. The procedure with 20% cold-pressing after heat-pressing is important to meet the expected demand for the rigidity.

　　Shandong University and USTC participate in the research and manufacture of readout electronics of the TGC of ATLAS muon spectrometer, in the research of level-l and level-2 trigger, in the development of background simulation software and in the alignment as well. The design, assemblage and test for the detectors of forward trigger muon system will be accomplished by collaborating with KEK of Japan, the assemblage of some of its components and the overall test will be done in China. The design scheme of the level-l and level-2 muon trigger system will be done together with Japan, Italy and CERN. The simulating calculation of the forward muon background, the design of optimum radiation shield and the development of the muon event reconstruction software will be accomplished by collaborating with Arizona University of US. Taken into account the characteristics of the error distribution caused by TGC system, the “maximum likelihood method” will be chosen in order to increase the precision of the track reconstruction.