Polarization Observables in Hard Rescattering Mechanism of Deuteron Photodisintegration

Abstract

Polarization properties of high energy photodisintegration of the deuteron are studied within the framework of the hard rescattering mechanism~(HRM). In HRM, a quark of one nucleon knocked-out by the incoming photon rescatters with a quark of the other nucleon leading to the production of two nucleons with high relative momentum. Summation of all relevant quark rescattering amplitudes allows us to express the scattering amplitude of the reaction through the convolution of a hard photon-quark interaction vertex, the large angle p-n scattering amplitude and the low momentum deuteron wave function. Within HRM, it is demonstrated that the polarization observables in hard photodisintegration of the deuteron can be expressed through the five helicity amplitudes of NN scattering at high momentum transfer. At 90$^\circ$ CM scattering HRM predicts the dominance of the isovector channel of hard $pn$ rescattering, and it explains the observed smallness of induced, $P_y$ and transfered, $C_x$ polarizations without invoking the argument of helicity conservation. Namely, HRM predicts that $P_y$ and $C_x$ are proportional to the $\phi_5$ helicity amplitude which vanishes at $\theta_{cm}=90^\circ$ due to symmetry reasons. HRM predicts also a nonzero value for $C_z$ in the helicity-conserving regime and a positive $\Sigma$ asymmetry which is related to the dominance of the isovector channel in the hard reinteraction. We extend our calculations to the region where large polarization effects are observed in $pp$ scattering as well as give predictions for angular dependences.