Two-body photodisintegration of the deuteron at forward angles and photon energies between 1.5 and 4.0 GeV

Abstract

It was discovered in experiments NE8 and NE17 at SLAC that the differential cross section near {theta}{sub cm} = 90{degrees} for the {gamma}d {yields} pn reaction at the highest measured photon energies (E{gamma} = 1.3-2.8 GeV) has an energy dependence consistent with the constituent counting rules. Experiment NE17 at SLAC indicates the s-dependence of the cross section is not consistent with constituent counting at forward angles. At CEBAF we proposed to measure the differential cross section at forward angles for two of the simplest exclusive binary reactions involving a deuteron in the initial or final state: (1) {gamma}d {yields} pn between E{yields} = 1.5 and 4.0 GeV, and (2) {gamma}d -{pi}{sup 0}d between E{gamma} = 1.0 and 3.0 GeV. This proposal was accepted by CEBAF PAC4 and was recently accorded high scientific priority by PAC7. The constituent counting rules predict an energy dependence of s{sup -11} and s-{sup 13} for the {gamma}d {yields} pn and {gamma}d {yields} {pi}{sup 0}d cross sections, respectively, where s is the square of the energy in the center of mass. Since more complex nuclei involve more constituents and consequently a more rapid falloff of the cross section as a function of s, these two cases may represent the only practical nuclear reactions that can be studied at large values of s where asymptotic scaling is most likely to be observed. These experiments are practical at CEBAF with the large beam current ({approximately}30 {mu}A) and the large solid-angle spectrometer. In particular, the CEBAF experiments will permit exploration of not only the scaling with photon energy, but also the transverse momenta in the reaction process. This experiment was selected as one of the commissioning experiments in Hall C and should take data in 1995.