On the application of differences in intrinsic fluctuations of Cherenkov light images for separation of showers

The sensitivity of ground-based imaging atmospheric Cherenkov γ-ray observatories depends critically on the primary particle identification methods which are used to retain photon-initiated events and suppress the spurious background produced by cosmic rays. We suggest a new discrimination technique which utilizes differences in the fluctuations of the light intensity in the images of showers initiated by photons and those initiated by protons or heavier nuclei. The database of simulated events for the proposed VERITAS observatory has been used to evaluate the efficiency of the new technique. Analysis has been performed for both a single VERITAS imaging telescope, and a system of these telescopes. We demonstrate that a discrimination efficiency of ⩾1.5–2.0 can be achieved in addition to traditional background rejection methods based on image shape parameters.