New data for totalHe3(γ,p)D andHe3(γ,pp)n cross sections compared to current theory

Abstract

A simultaneous measurement of the cross sections of the $^{3}\mathrm{He}$($\ensuremath{\gamma},p$)D and $^{3}\mathrm{He}$($\ensuremath{\gamma},\mathit{pp}$)n reactions has been performed for the first time using monoenergetic pulsed \ensuremath{\gamma}-rays at $\ensuremath{\langle}{E}_{\ensuremath{\gamma}}\ensuremath{\rangle}=$10.2 and 16.0 MeV. Charged fragments from the reactions were detected with an efficiency of 100% using a 4\ensuremath{\pi} time projection chamber containing $^{3}\mathrm{He}$ gas as an active target. The incident \ensuremath{\gamma}-ray flux was measured by a \ensuremath{\gamma}-ray detector. Both the track and energy loss signals of charged fragments were obtained in an off-line analysis and used to clearly identify the reaction channel. Thus, the ($\ensuremath{\gamma},p$) and ($\ensuremath{\gamma},\mathit{pp}$) cross sections have been determined with small uncertainty. A comparison of the new data to current theory based on the AV18+Urbana IX nuclear forces including \ensuremath{\pi}- and \ensuremath{\rho}-like meson exchange currents shows a severe discrepancy at 10.2 MeV, while at 16.0 MeV data and theory agree within about 12%. Three-nucleon force effects are small, but in general shift the theory in the correct direction.