Calibration Procedure and Results for the GlueX Start Counter

The GlueX start counter is the central detector of the GlueX experiment. It is composed of 30 scintillating plastic paddles that cylindrically surround the liquid hydrogen target.

The Start Counter provides a solid angle coverage of approximately 90% of 4pi. It is designed to operate for tagged photon intensities of up to 10^7 gamma/s.

Its main purpose is to identify the beam pulse associated with an event. For this a timing resolution in the range of 500 to 825 ps is required; a resolution of roughly 350 ps has been observed. The detector and its calibrations have been previously described by E. Pooser et al..

We will present the start counter design and explain the importance of time walk and pathlength corrections. Then we will present results from the calibrations for the PrimeX eta experiment and the current Phase II run of GlueX.