LEPS2實驗將在2013年於日本SPring-8開始取數。 一組4pi維度的偵測器正在研發當中，其中高阻抗平板偵測器(Multi-gap Resistive Plate Chamber－MRPC)為量測粒子飛行時間的偵測器。 為了在飛行距離約為一公尺中分辨動量為 1.5 GeV/c 的 K 和 pi 兩種粒子，高阻抗平板偵測器必須到達 50皮秒 的時間解析度及 99 % 以上的效率。 為了最佳化我們的高阻抗平板偵測器，我們研究了偵測器輸出的幾何形狀、氣體成分、放大器、、、等等。目前為止，我們決定了高阻抗平板偵測器的結構和輸出板的大小。 260 微米 x 5 gaps x 2 層的高阻抗平板偵測器，在 2.5 x 100 平方公分輸出板下，其可以到達 60 皮秒的時間解析度及 99 % 的效率。 整個量測飛行時間的系統約需要400個電子通道。將來我們將會繼續研究放大器和氣體成分。The LEPSII experiment is scheduled to start in 2013. The development of a 4 pi detectors and the construction of a solenoid magnet is currently underway. In order toseparate K and pi with momenta up to 1.5 GeV/c using Time-of-Flight (TOF) over a distance of about 100 cm in the magnet, Multi-Gap Resistive Plate Chamber (MRPC) operated in avalanche mode is chosen due to the need of large area, high e ciency and 50-ps time resolution. For optimizing the best con guration of MRPC, we investigated geometry of pad/strip, width of gap, number of gap, the gas mixture, trigger rate, etc. The 260um x 2 stacks x 5 gaps MRPC with the 2.5 x 100 cm2 strip reached 99 % effi ciency and around 60-ps time resolution below 20 Hz/cm2. The chamber was filled with gas mixture of 90 % R134a, 5 % SF6 and 5 % Iso-butane. The signals were ampli ed by PMT Amp (KN2104). We needs around 400 channels to cover the whole area of TOF system. The performance of MRPC is close to LEPSII requirement. The gas mixture and the ampli er will be investigated in the future.
