J. Bowles

The HERMES recoil detector

The HERMES recoil detector is an exciting addition to the HERMES spectrometer, specifically designed to make one of the first exclusive measurements of deeply virtual Compton scattering (DVCS). DVCS is the experimentally cleanest way to access generalised parton distributions - a theoretical framework that describes the structure of the nucleon. The recoil detector utilises a silicon detector with a large dynamic range capable of reconstructing the momenta of protons in the range of 135 MeV/c to 450 MeV/c, placed directly into the HERA beam vacuum (around the HERMES target) to make both position and energy deposition measurements (for the purposes of momentum reconstruction) of the recoil protons from the process. In addition there is a scintillating fibre tracking (SET) detector placed directly outside the beam vacuum that provides both tracking information and momentum reconstruction data for protons at higher momenta. The third sub-detector is a photon detector that lies concentrically outside the SET and provides useful information on other processes for the purposes of background subtraction. Leptons involved in the interaction will be detected in the existing parts of the HERMES spectrometer. The recoil detectors silicon sub-detector was the subject of a presentation at the IEEE NSS in 2003 by Mathias Reinecke. This presentation is intended as an update on the successful development of the silicon sub-detector as well as providing more information on the impending installation of the detector into the HERMES spectrometer in November 2005