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

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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.