Quantitative evaluation of V_B-mediated coherent deuteron photoproduction

Determine quantitatively the contributions of the representative nucleon-triggered vector-boson $V_{\mathcal B}$-mediated two-nucleon exchange amplitudes, and their interference with conventional amplitudes, to coherent $\gamma d\to\pi^0\eta d$ and $\gamma d\to\pi^0\pi^0 d$ photoproduction.

Background

The paper proposes that the same nucleon-triggered vector boson $V_{\mathcal B}$ invoked to explain production-dependent discrepancies in rare $\eta^{(\prime)}\to\pi^0(\eta)\gamma\gamma$ decays may generate two-nucleon exchange amplitudes in coherent deuteron photoproduction. The proposed mechanisms involve two insertions of the effective $(\bar N N)V_{\mathcal B}P\gamma$ interaction, allowing the two nucleons in the deuteron to exchange momentum through $V_{\mathcal B}$ while producing the observed meson pair.

The suggested amplitudes could contribute to the unexpectedly flat deuteron angular distributions reported for both $\gamma d\to\pi^0\eta d$ and $\gamma d\to\pi^0\pi^0d$, which are not reproduced by existing conventional calculations. The paper identifies representative diagrams but does not calculate their magnitudes or their interference with Standard Model one- and two-nucleon mechanisms; consequently, establishing whether these contributions can account quantitatively for the observed angular-distribution discrepancies remains unresolved.