The Development of 2 m long multi-gap RPC for LEPS2 experiment

We developed multi-gap RPCs with 2 m long strips for LEPS2 experiment. LEPS2 experiment at the SPring-8 in Japan aims to study hadron physics from photo-production reactions. The High rate, high energy and high polarization γ beam irradiates a target. We detect the produced particles by a solenoid spectrometer covering the polar angle region of 5-120 degrees. The 2m long RPCs will be installed into the solenoid magnet cylindrically, which are 0.9m away from the target. They are used as Time-of-Flight (TOF) counters for particle identification (π/K/p). These RPCs are required below 75 ps time resolution (σ) for 3 σ separation. In the previous work, we achieved around 50 ps resolution of 1 m long RPCs. We also developed 2 m RPCs having 65 ps resolution. But since oscillation of preamp often occurred, it was difficult to operate this 2 m chamber stably. 

We improved the ground around the preamps and we succeeded the noise suppression. In added, we changed several points. We studied the performance of these chambers. We find that they have about 60 ps resolution and over 99% efficiency. In this presentation, I will talk about several improvement and the performance test.