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

我们研制了用于在中国核子研究中心通过pn-pΛ反应产生弱Λ超子的实验的触发系统。弱衰变Λ发出的带负电荷的介子才是反应的真实信号。因此，有必要区分带负电荷的介子和大量带正电荷的背景质子。我们在圆柱形漂移室内外安装了两套塑料计数器。为了辨别负电荷粒子，外部计数器的每一段都沿径向倾斜。开发工作已于2000年完成。2001年，我们开发了新型的外置计数器。到目前为止，闪烁光是由直接耦合的光电管读出的。为了扩大计数器系统的接受度，我们安装了波长移位光纤和多阳极光电管相结合的计数器读数。这种方法已经建立，并已用于内部计数器。我们在2001年12月和2002年2月进行了测试实验。尽管分析仍在进行中，但我们确认，与背景质子相比，我们可以在触发水平上区分负电荷的介子。

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.