Coherent pion photoproduction on deuterium at momentum transfer $|t|$ up to 2.2 (GeV/$c$)$^2$}

The reaction $\gamma d \rightarrow \pi^0d$ was measured with the CLAS detector at the Thomas Jefferson National Accelerator Facility at photon energies between 0.54 and 2.0 GeV and pion CM scattering angles between 50$^\circ$ and 150$^\circ$. The total CM energy $s$ varied between 5.5 and 12 GeV$^2$. At pion backward CM angles the scaled invariant cross sections $s^{13}\frac{d\sigma}{dt}$ vary about a constant value as a function of $s$. These variations are most probably due to soft-scattering contributions. Fits to the dependence of $\frac{d\sigma}{dt}$ on $s$ at fixed $\theta^\pi_{CM}$ show that for $\theta^\pi_{CM}>100^\circ$ our data are generally consistent with the predictions of the Constituent Counting Rules (CCR) $[1]$. The predictions of the Reduced Nuclear Amplitudes (RNA) approach $[2]$ are consistent with the data at $-t>1.4$ (GeV/$c$)$^2$ and $s>7$ GeV$^2$. Comparisons with other exclusive processes and traditional meson-nucleon models will be discussed. \vspace{6mm} \newline 1. S.J. Brodsky and G.P. Lepage, Perturbative Quantum Chromodynamics, SLAC-R-224, 133 (1979) \\ 2. S. Brodsky, J.R. Hiller, Chueng-Ryong Ji and G.A. Miller, Phys. Rev. C \textbf{64}, 055204 (2001)