Test of a 3 m long, 4 × 4 cm2 time-of-flight (TOF) scintillation counter using 38 × 38 mm2 fine-mesh photomultipliers in magnetic fields up to 1.5 T

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-1, at the KEK-PS. The counter of a 3 m long scintillator bar (BC-408) of 4 × 4 cm2 in cross section is viewed by a newly developed 38 × 38 mm2 square-shaped fine-mesh photomultiplier tube at each end. In the first test the time resolution for a single photomultiplier after being corrected 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 direction when the beam was perpendicularly incident at the middle of the counter, and it was found to be essentially constant in the magnetic field range below 1.2 T. This result implies that the prototype TOF counter with two fine-mesh photomultipliers can give a time resolution of about 100 ps in this field range. In the second test after the scintillator surface was damaged time resolutions were measured in magnetic fields up to 1.5 T. Data indicate a slight degradation in time resolution with increasing magnetic field above 1 T. The time resolution becomes poorer by about 20% at 1.5 T compared with those below 1 T.