Improving the angular resolution for the silicon detectors of the STARS array

The STARS (Silicon Telescope Array for Reaction Studies) array at LBNL is used to measure the emission angles of light charged particles (protons, deuterons and tritons) following transfer reactions. The array consists of two CD-shaped silicon energy detectors: a thin ``delta E'' detector and a thicker ``E'' detector, each segmented into twenty-four concentric rings. The angle at which a particle hits the delta E detector is typically approximated in the off-line analysis code as the angle from the beam axis to the center of the ring traversed by the particle. To improve angular resolution, a new method of approximating the angle was investigated. It was thought that energy loss in the delta E could be used to derive angle. SRIM was used to create functions of energy loss per unit distance with respect to particle energy. These functions were used in Fortran codes to create matrices of energy loss for a range of angles and final energies. The matrices were then worked into the off-line analysis code. Preliminary results will be shown. This work is partly supported by the DOE under grant numbers DE-FG02-52NA26206 and DE-FG02-05ER41379.