Development of amplifier with pulse shaper for high rate MWPC

An amplifier has been developed for wire chambers used as an in-beam detector for charged particles in the KOTO experiment, which aims at discovering a CP-violating rare decay of long-lived neutral K meson, K_L → p⁰νν Due to in-beam condition of the wire chambers, the maximum counting rate is estimated to reach 700 kHz per channel. Because the output signals of the wire chambers have a long tail of low frequency components coming from slow drift of ions which remains tens of microseconds, pulse pile-up and baseline fluctuation are expected in such a high rate operation. In order to suppress these undesirable phenomena, a pulse shaping circuit was integrated into the signal amplifier for the wire chamber, which consists of three pole-zero cancellation networks. The performance of the pulse shaping circuit was confirmed by using a prototype single-channel MWPC. The achieved pulse width was 40% of the original one in FWHM. The total pulse width was 150 ns, where any long tail exceeding the total width vanished.