Test of QCD from measurement of the lifetime ofπィイD1+ィエD1πィイD1-ィエD1 atoms using a fast topological trigger system

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Test of the quantum chromodynamics (QCD) is important in order to discover and phenomena beyond the standard model of elementary particle physics. Although QCD is known to hold pretty well at high energies, test of QCD at low energies is not easy since calculation has to be carried out without using perturbative method due to the large coupling constant in Lagrangian. We have planned an experiment, called DIRAC, of measuring the decay lifetime of πィイD1+ィエD1πィイD1-ィエD1 atoms to πィイD10ィエD1πィイD10ィエD1 at CERN PS to test the predictions of CHPT, the effective theory of QCD at low energies, to an accuracy of 5%, and started data-taking in 1999. In this experiment, it is important to detect precisely two minimum-ionising particles at short distances (<5-6 mm) within 100 ns after the occurrence of the event. We developed necessary fast Scifi and dE/dx detectors for position and dE/dx measurements, respectively. While we detect πィイD1+ィエD1πィイD1-ィエD1 pairs coming from dissociation of πィイD1+ィエD1πィイD1-ィエD1 atoms in DIRAC, direct detection of decay πィイD10ィエD1πィイD10ィエD1 should have a merit for improved experiment in future. So, we also carried out R&D for fast, heavy and radiation-hard scintillators for excellent g-ray detectors.1. Scifi-detectors and fast triggering electronics were successfully constructed and are now in use.2. We have succeeded in developing (1) Si-detectors (64x64mmィイD12ィエD1 in size, 300μm thick and read-out at a step of 1-2mm), (2) charge preamplifier with decay time of 100-240 ns and ENC of 3000e, and (3) shaping amplifier of gain 50 and pulse width of 50 ns. This will replace the present dE/dx detectors of plastic-scintillato strips from 2001.We have made significant improvement in heavy, fas and radiation hard scintillators such as PbWOィイD24ィエD2, GdィイD22ィエD2SiOィイD25ィエD2:Ce, etc.