A double pulse separator for a lifetime measurement of pionic atoms.

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A validity of QCD has not been proved yet at low energy region, where the interaction between quarks is too strong to be treated as a perturbation. The aim of this research is to test the QCD at an unperturbed low energy by measuring a life time of pionic atoms A_<2pi>(bound state of pi+pi-) with 10% accuracy. (DIRAC CERN-PS212) The life time of A_<2pi> is related to the scattering length of pi-pi scattering in S-state and is preciesly predicted by a Chiral perturbation theory. To extract real rare A_<2pi> events from huge amount of background events experimentally, we have to develop a new type trigger device providing some topological information in the real time. The topological trigger device employed here consists of scintillating fiber hodoscopes (SCIFI) followed by position sensitive photo-multipliers (PSPM) and double constant fraction discriminators(DCFD) for a delay-line read-out device giving distances among multiple hit particles.Analog signals from multi-anodes of the PSPM were read by means of delay line method to reduceelectronic modules and were converted to timing signals by the double side CFDs. Performances of them were tested by using high energy secondary particles produced by 24GeV protons. The double pulse separation was found to be good for the double pulses with an interval larger than 1.5 nsec, which corresponds to 1.5mm distance beteen the two particles on the hodoscope, The two particle identification efficiency, position resolution and time resolution were measured and were satisfactorily good. We found that the hodoscope with 5 layers of 0.5mm SCIFI was a little bit thin to give a stable pulse shape for the DSCFD and didn't give a well separation at the distance less than 1.5mm.We found that when the DCFD devices are used for dinode output together with anode signals, such infomation as a time difference and a position distance between two particles needed for trigger devices can be obtained in real time.