Parity violation in deuteron photodisintegration

We analyze the energy dependence for two parity-nonconserving (PNC) asymmetries in the reaction $\gamma D\to np$ in the near-threshold region. First, we analyze the asymmetry in the reaction between a circularly polarized photon beam and an unpolarized deuteron. Second, we examine the reaction between an unpolarized photon and a polarized deuteron. We find that the two asymmetries have quite different energy dependence, and that the shapes are sensitive to the PNC meson-exchange coupling constants. The constraints for the PNC coupling constants and how to obtain them from future experiments are discussed.

Figure 1

(Color online) The total cross section of the deuteron photodisintegration as a function of the energy excess $\Delta E_{\gamma }=E_{\gamma }-E_{\text{thr}}$. (a) Result for the Paris potential. Contributions of the $M1$ and $E1$ transitions are shown by the dashed and dot-dashed curves, respectively. (b) The total cross section for the Paris (solid) and Hamada-Johnston (dashed) potentials. The experimental data on the total cross section are taken from Refs. 38 (open circles) and [39] (filled circles). The data on $M1$-transition (filled squares) are taken from Ref. 40.

Figure 2

The odd-parity admixture to the proton-neutron wave functions calculated with the Paris (solid curves) and HJ (dashed curves) potentials. (a) Results for the deuteron wave functions. (b) and (c) Results for the continuum $np$ wave functions at $\Delta E_{\gamma }=0.1$ and $1\text{MeV}$, respectively.

Figure 3

Asymmetry of the deuteron disintegration in the reaction $\gamma D\to pn$ with circular polarized photon and unpolarized deuteron as a function of the energy excess $E_{\gamma }-E_{\text{thr}}$. (a) Relative contribution of the different odd-parity transitions for the Paris potential. The sign in the bracket denotes the sign of the corresponding term. (b) Comparison of the total asymmetry for the Paris (solid), Hamada-Johnston (dashed) potentials, and the modified ZRA of Ref. 29 (dot-dashed).

Figure 4

Asymmetry of the deuteron disintegration in the $\gamma D\to pn$ reaction with polarized deuteron and unpolarized photon as a function of the energy excess $E_{\gamma }-E_{\text{thr}}$. (a) Relative contribution of different odd-parity transitions for the Paris potential. Notation is the same as in Fig. 3a. (b) Comparison of the asymmetry for the Paris and Hamada-Johnston potentials.

Figure 5

Asymmetry of the deuteron disintegration in the $\gamma D\to pn$ reaction $\left(A_D\right)$ with different values of the PNC $\pi$-exchange coupling constant $R=h_{\pi }∕h_{\pi }^{\text{best}}=0,1,2.5$, where $h_{\pi }^{\text{best}}$ is the best value of Ref. 3.

Figure 6

(a) The quantities $a_i$ of Eq. (35). (b) The quantities $b_i$ of Eq. (36). Only the large components are displayed. Results are obtained with the Paris potential.