A test of QCD by measuring a life-time of hadoronic 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. (DIRACCERN-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), peak sensing circuit (PSC) for a read-out device, and a trigger logic circuit (TLC) giving distances among multiple hit particles.During 1995-1996, a scintillating fiber ho … More doscope and a peak sensing circuit were designed and prototypes of them were constructed. Their performances were tested by using high energy secondary particles produced by 24GeV protons. We measured such fundamental properties needed for our toporogical trigger device as an attenuation length of a scintillating fiber, a time resolution, an uniformity of pulse height distribution, cross talk among channels, a detection efficiency, an ability of multi-particle identification etc. At the same time, triggering patterns and triggering rates characteristic of the decay from the pionic atoms and those of competing background processes to be rejected were studied by a Monte Carlo simulation. Based on the simulation and the experimental results, the final design of the best suited triggering logic circuit was drawn.In 1997, a complete set of a real size topological trigger device was constructed and tested the performance as a whole by using beam. The experimental results obtained from the trigger device were compared with the precise off-line analysis and/or the Monte Carlo simulation, and showed that the device can generate topological trigger signals with satisfactorily high performance in the event identification, time resolution, position resolution, triggering speed, detection efficiency, and partlicle multiplicity identification.After the autumn in 1998, this trigger device will be used for thr DIRAC experiment as a second level trigger generator. Less