Measurement of the high energy γ -rays from heavy ion reactions using Čerenkov detector

The energetic bremsstrahlung photons up to 100 MeV produced in heavy ion collisions can be used as a sensitive probe for short-range correlation in atomic nuclei. The energy of the γ -rays can be measured by collecting the Čerenkov light in the medium induced by the fast electrons generated in the Compton scattering or electromagnetic shower of the incident γ ray. Two types of detectors based on pure water and lead glass as sensitive materials were designed for this purpose. The γ response and optical photon propagation in the detectors were simulated based on electromagnetic and optical processes in Geant4. The inherent energy resolutions of 0.022(4)+0.51(2)/E_γ^1/2 for water and 0.0026(3)+0.446(3)/E_γ^1/2 for lead glass were obtained. The geometry sizes of the lead glass and water were optimized to 30 cm × 30 cm × 30 cm and 60 cm × 60 cm × 120 cm, respectively, to detect high-energy γ -rays at 160 MeV. The Hough transform method was applied to reconstruct the direction of the incident γ -rays, providing the ability to experimentally distinguish the high-energy γ -rays produced in the reactions on the target from random background cosmic-ray muons.