Reduced nuclear helicity amplitudes for deuteron electrodisintegration and other processes

Abstract

We extend the original idea of reduced nuclear amplitudes to capture individual helicity amplitudes and discuss various applications to exclusive processes involving the deuteron. Specifically, we consider deuteron form factors, structure functions, tensor polarization observables, photodisintegration, and electrodisintegration. The basic premise is that nuclear processes at high momentum transfer can be approximated by tree graphs for point-like nucleons supplemented by empirical form factors for each nucleon. The latter represent the internal structure of the nucleon, and incorporate nonperturbative physics, which can allow for early onset of scaling behavior. The nucleon form factors are evaluated at the net momentum transfer experienced by the given nucleon, with use of G E for a no-flip contribution and G M for a helicity-flip contribution. Results are compared with data where available. The deuteron photodisintegration asymmetry Σ is obtained with a value of Σ(90 • ) ≃ −0.06, which is much closer to experiment than the value of -1 originally expected. The method also provides an estimate of the momentum transfer values required for scaling onset. We find that the deuteron structure function B is a good place to look, above momentum transfers of 10 GeV 2 .From these we can calculate the various observables. Plots of the results and recent data [48][49][50] are given in Figs. 14,15,16,and 17. Because the tree-level amplitudes are real, P y is automatically zero. That C x ′ is of order m/ √ s, rather than zero, is a correction to hadron helicity conservation [51]. Also, we find the asymmetry Σ(90 • ) to be approximately -0.06, rather than the nominal expectation [52] of -1. In general, the trends with photon energy seem to be modestly consistent with data.