Response of cooled PWO scintillators to low-energy gamma-rays and its importance in studies of the h c →η c + γ transition in charmonium

Abstract

Suppression of non-resonant background due to emission of π0 increases signal to background ratio in γ-ray emission studies between the discrete states of charmonium. We demonstrate with Monte-Carlo simulations how π0 identification capability increases with decreasing threshold for γ-ray detection in π0 decay. An apparatus has been designed and measurements of the FWHM resolution performed for the three energies 6.13, 12.7 and 16.9 MeV. The trend established in the 50–650 MeV energy range is corroborated.