Use of sum signals of ionization and scintillation in liquid rare gases and the Fano factor for the sum signals

Scintillation signals and ionization signals produced in liquid rare gases by ionizing radiation can be simultaneously observed with high efficiencies. The fluctuation of the sum of scintillation and ionization signals is smaller than that of either of the individual signals. The present paper discusses the theoretical limit of energy resolution of the sum signals, compares it with the experimental results obtained in liquid rare gases, and presents comments recent papers treating related topics