Time-of-flight resolution of scintillating counters with Burle 85001 microchannel plate photomultipliers in comparison with Hamamatsu R2083

Improvements in the time resolution of the CEBAF Large Acceptance Spectrometer (CLAS) below ≈ 50 ps will be required for experiments using the planned upgraded accelerator facility at Jefferson Lab. The improved time resolution will allow particle identification using time-of-flight techniques to be used effectively up to the proposed operating energy of 12 GeV . The challenge of achieving this time resolution over a relatively large area is compounded because the photomultipliers (PM) in the CLAS “time-zero” scintillating counters must operate in very high magnetic fields. Therefore, we have studied the resolution of “time-zero” prototypes with microchannel plate PMs 85001-501 from Burle. For reference and comparison, measurements were also made using the standard PMs R2083 from Hamamatsu using two timing methods. The cosmic ray method, which utilizes three identical scintillating counters (Bicron BC-408, 2 × 3 × 50 cm 3 ) with PMs at the ends, yields σ R 2083 = 59.1 ± 0.7 ps . The location method of particles from a radiative source with known coordinates has been used to compare timing resolutions of R2083 and 85001-501. This method yields σ R 2083 = 59.5 ± 0.7 ps and it also provides an estimate of the number of primary photoelectrons. For the microchannel plate PM from Burle the method yields σ 85001 = 130 ± 4 ps due to lower number of primary photoelectrons.