s . in s - de t ] 1 6 M ay 2 00 7 A large acceptance scintillator detector with wavelength shifting fibre read - out for search of eta - nucleus bound states

A large acceptance scintillator detector with wavelength shifting optical fibre readout has been designed and built to detect the decay particles of η-nucleus bound system (the so-called η-mesic nuclei), namely, protons and pions. The detector, named as ENSTAR detector, consists of 122 pieces of plastic scintillator of various shapes and sizes, which are arranged in a cylindrical geometry to provide particle identification, energy loss and coarse position information for these particles. A solid angle coverage of ∼95% of total 4π is obtained in the present design of the detector. Monte Carlo phase space calculations performed to simulate the formation and decay of η-mesic nuclei suggest that its decay particles, the protons and pions are emitted with an opening angle of 150◦ ± 20◦, and with energies in the range of 25 to 300 MeV and 225 to 450 MeV respectively. The detailed GEANT simulations show that ∼ 80 % of the decay particles (protons and pions) can be detected within ENSTAR. Several test measurements using alpha source, cosmic-ray muons etc. have been carried out to study the response of ENSTAR scintillator pieces. The inbeam tests of fully assembled detector with proton beam of momentum 870 MeV/c from the Cooler synchrotron COSY have been performed. The test results show that