Measurement of the total photoabsorption cross section on a proton in the energy range 600–1500 MeV at the GRAAL

Abstract

The total photoabsorption cross section on a free proton was measured at the GRAAL facility in the energy range Eγ = 600−1500 MeV. The large-aperture LAGRANγE detector and a liquid hydrogen target were used in the experiment performed with a back-scattered Compton gamma beam. To improve the accuracy, two alternative methods were employed. First, a subtraction method of using empty-target measurements allowed the cross section σtot to be evaluated directly because of a low level of the electromagnetic background. Second, an algorithm for evaluating σtot on the basis of summing the dominating partial cross sections was developed. Experimental results obtained for σtot by the two methods are compared with existing data.