Three-body Forces in Photoreactions on 3He

Abstract

We have measured the three-body photobreakup of {sup 3}He with the tagged photon beam and the CEBAF Large Acceptance Spectrometer in Hall B at the Thomas Jefferson National Accelerator Facility, in the photon energy range between 0.35 GeV and 1.55 GeV. This measurement constitutes a wide-ranging survey of two- and three-body processes in the gamma{sup 3}He {yields} ppn reaction channel, thanks to the high statistics and large kinematic coverage obtained with the CLAS. Total and partially integrated differential cross sections for the full ppn data set and for selected kinematics were extracted and are compared to theoretical predictions of Laget (up to 1.0 GeV). At low photon energies, the calculations are generally in fair agreement with the data. The comparison shows evidence of strong contributions of three-body absorption mechanisms, especially in the star kinematics, a symmetric configuration of the three final-state nucleons. Mostly the effects of two-body absorption mechanisms are se en, as expected, in the pp-pair-breakup kinematics, where the neutron does not participate in the reaction. The quasi-two-body breakup shows angular distributions consistent with preliminary gamma{sup 3}He --> pd results, extracted from our experiment. The ratio of cross sections for the star configuration and for the two-body kinematics, showsmore » a maximum for three-body effects at a photon energy of about 0.5 GeV, corresponding to a reduced photon wavelength of 0.4 fm. The 4pi-integrated cross section is in excellent agreement with previous experimental results from DAPHNE up to 800 MeV; no previous results have been obtained above this energy.« less