TEST OF A 3M LONG, 4X4 CM(2) TIME-OF-FLIGHT (TOF) SCINTILLATION-COUNTER USING 38X38 MM(2) FINE-MESH PHOTOMULTIPLIERS IN MAGNETIC-FIELDS UP TO 1.5T

A prototype time-of-flight counter for the CDF detector was tested in magnetic fields up to 1.5 T using a test beam line of 2 GeV/c, T-l, at the KEK-PS. The counter of a 3 m long scintillator bar (BC-408) of 4 x 4 cm(2) in cross section is viewed by a newly developed 38 x 38 mm(2 ) square-shaped fine-mesh photomultiplier tube at each end. In the fir st test the time resolution for a single photomultiplier after being c orrected for the contribution from a reference counter was measured to be about 130 ps in a magnetic field of 1.2 T in the tube axial direct ion when the beam was perpendicularly incident at the middle of the co unter, and it was found to be essentially constant in the magnetic fie ld range below 1.2 T. This result implies that the prototype TOF count er with two fine-mesh photomultipliers can give a time resolution of a bout 100 ps in this field range. In the second test after the scintill ator surface was damaged time resolutions were measured in magnetic fi elds up to 1.5 T. Data indicate a slight degradation in time resolutio n with increasing magnetic field above 1 T. The time resolution become s poorer by about 20% at 1.5 T compared with those below 1 T.