Research On The Time-of-Flight System In The CSR External-target Experiment

The Quantum chromodynamics(QCD)phase structure and the equation of state of nuclear matter are hot spots and frontiers in the field of nuclear physics research.In recent years,relativistic heavy ion collision experiments such as ALICE and STAR have made major breakthroughs in these research fields,especially the latest results from RHIC BES-I show that the QCD phase transition critical point and other new physics related to the phase structure may occur in the region of low-temperature and highbaryon density.The QCD phase diagram in the low-temperature and high-baryon density has become the focus of the current international frontier.In order to take a leading position and make breakthroughs in this research direction with potentially major discoveries,Chinese nuclear physicists proposed to use the existing Heavy-ion Research Facility-Cooler Storage Ring in Lanzhou(HIRFL-CSR)and the High Intensity Heavyion Accelerator Facility(HIAF)under construction to build a universal low-temperature and high-baryon density nuclear matter measurement spectrometer-CEE.The CEE will be the first large-scale heavy ion physics experimental spectrometer in the medium and high energy region in China.It focuses on frontiers of physics research in the lowtemperature and high-baryon density region,and has important scientific significance for exploring the QCD phase diagram structure and the physics of nuclear matter in this energy region.It is expected to make China enter the forefront of the world in this field of physics research.The CEE spectrometer mainly measures the charged final-state particles.The Time-of-Flight(TOF)system will become an important means of identifying charged final-state particles in the CEE due to its simple principle,compact structure and simple fabrication.The purpose of this paper is to develop a high performance TOF system for CEE spectrometer,including the inner TOF(iTOF)and the starting time detector(T0).The research goal is to achieve π/K/p discrimination of 3σ in the range of>95%momentum coverage of the CEE.The time requirement of the TOF system for iTOF and T0 is to achieve a time resolution of about 30～40 ps respectively.The author designs the structures of iTOF and T0 through simulation and calculation,and selects a Multi-gap Resistive Plate Chamber(MRPC)with high time performance and high detector efficiency as the detector of iTOF according to the requirements of the CEE.The scintillation detector with compact structure and excellent time performance is selected as the detector of T0.The author participated in the design,production and batch testing of CBM-TOF and STAR-eTOF upgraded MRPC at master’s study,and is familiar with the working principle,basic structure and production process of MRPC.Compared with CBMTOF and STAR-eTOF,the flight distance of CEE-iTOF charged final-state particles is shorter,which puts forward higher requirements for time performance.The time resolution of the traditional MRPC based on time digital readout technology is greater than 50 ps,and it does not meet the about 30～40 ps time resolution requirement of the CEE iTOF.Based on the traditional MRPC design,the author made breakthroughs and innovations in MRPC technology.A four-stacked 24-gas-gap MRPC is designed,and the MRPC time performance is improved by studying the signal integrity and optimizing the readout scheme.The cosmic ray test results show that the detection efficiency of the developed MRPC prototype is higher than 96%,and the time resolution is better than 38 ps.Compared with the traditional design,the time accuracy of iTOF MRPC is improved by 12 ps,which well meets the needs of CEE and the future generation nuclear and particle physics experiments with higher precision time measurement.The T0 is located on the beam line and provides a starting time for TOF system by measuring the beam arrival time.The author innovatively proposes a technical solution for T0 based on plastic scintillator coupled with SiPMs,which not only meets the needs of different types of beams,but also has the advantages of compact structure and wide dynamic range.The paper introduces the design of T0 in detail,including detector structure design,performance simulation,performance test and time calibration algorithm research.The GEANT4 simulation and heavy ion beam test results show that the designed T0 has a time resolution of～20 ps,which is much better than the technical specifications.