Development of charge-sensitive trigger system for study of weak production of hyperon

我们在RCNP实验室研制了一套触发系统，通过pn-pΛ反应弱产生Λ超子。由弱衰变Λ发出的带负电荷的π介子是反应的真正信号。因此，有必要将带负电荷的π介子与大量带正电荷的背景质子区分开来。我们在圆柱形漂移室的内外安装了两套塑料计数器。为了区分负电荷粒子，外部计数器的每一段都相对于径向倾斜。该开发已于2000年完成。2001年，我们开发了新型的外柜。迄今为止，闪烁光的读出都是通过直接耦合的光电管实现的。为了扩大计数器系统的接受范围，我们安装了波长移位光纤和多阳极光电管组合读出的计数器。这种方法已经建立并用于内部计数器。我们于2001年12月和2002年2月进行了测试实验。虽然分析仍在进行中，我们确认，我们可以歧视的负电荷π介子的触发水平相比，背景质子。

We developed the trigger system used for the experiment at RCNP where we produced Λ hyperon weakly by pn-pΛ reaction. Negative-charged pion emitted by weak decay Λ is the genuine signal of the reaction. Therefore it is necessary to discriminate negative-charged pion from a vast amount of background proton, which has positive charge. We installed two set of plastic counters inside and outside of cylindrical drift chamber. To discriminate negative-charge particles, each segment of the outer counters is tilted respect to the radial direction.The development has been finished in 2000. In 2001, we developed new type of outer counters. So far, the scintillation light is read out by directly coupled phototubes. In order to extend the acceptance of the counter system, we installed the counters read by the combination of wave-length shifter fiber and multi-anode phototubes. This method has already established and been used for the inner counters. We carried the test experiment on December, 2001 and February, 2002. Although the analysis is still under going, we confirm that we can discriminate negative-charge pion on the trigger level compared to background protons.