Cosmic-ray test of a time-of-flight detector for double-strangeness experiments at J-PARC

We have developed a time-of-flight (ToF) array consisting of 24 plastic scintillators for triggering and timing measurements in a series of planned experiments to study double-strangeness hadronic and nuclear systems at the K1.8 beamline of J-PARC. Each ToF scintillator is 180 cm long with a cross-section of 8×3cm2, and is read out by H1949-50 photomultiplier tubes at both ends. The timing and attenuation properties of the scintillators are measured using cosmic-ray muons and β rays from 90Sr. The cosmic-ray muon events are triggered by three pairs of 120-cm-long plastic scintillators, sandwiching the ToF array. The intrinsic time resolutions of the scintillators are estimated to be in the range 60-100 ps, which is adequate for reliable separation between π and K at 1.2GeV/c. The attenuation length is measured to be approximately 210 cm, which is half that for a bulk scintillator.