Status and possibilities of the time-of-flight measurement technique using long scintillation counters with a small cross section (Review)

Results of the analysis of the state-of-the-art time-of-flight measurement technique with the use of long scintillation counters with a small cross section (the length of the counter far exceeds its width in the plane of the hodoscope and thickness along the beam direction), which are used as basic elements of time-of-flight detectors for large physical installations and intended for identifying secondary particles generated during collisions of high-energy particles. The following issues are considered in this review. Various methods for identifying particles are compared, and it is pointed out that the time-of-flight method has certain advantages for secondary particles with momenta higher than ∼3–5 GeV/c. Some elements incorporated in scintillation counters and affecting its time resolution are considered: optical fibers, optical contacts in the scintillator-fiber-photodetector system, and high-frequency cables. Their characteristics are presented. The characteristics of all elements of a counter (scintillator, photodetector (PD), and electronics) and the processes occurring in them are discussed. The presented experimental data show that, under the conditions of high counting rates and strong magnetic fields, the working capacity of counters holds at a time resolution of ∼100–200 ps. The results of measuring the operating characteristics of counters are analyzed. The dependences of the time resolution on such variables as the coordinate of the particle transit through a counter along its length, the counter length, the light-absorption length in the scintillator, the quality of treatment of the scintillator’s surface, and the energy deposited by a particle in the scintillator substance are considered. The main characteristics of individual time counters and average parameters of time-of-flight detectors in certain physical facilities are presented. Possible ways to improve the time resolution and reduce it to ∼50–100 ps are considered.