Coherent π0-photoproduction on the deuteron near the η-production threshold including polarization observables

Coherent pi(0)-photoproduction on the deuteron including polarization observables is studied in the energy region near the eta-production threshold at backward center-of-mass angles of the outgoing pion. This work is motivated by the measurements of the CLAS Collaboration at Jefferson Lab, where a cusp-like structure in the energy dependence of the differential cross section has been observed at extremely backward pion angles. The present approach is based on the impulse approximation and first-order rescattering diagrams with intermediate production of both pi- and eta-mesons. Numerical results for unpolarized cross sections, the linear photon asymmetry (Sigma), the vector (T-11) and tensor (T-2M, M = 0, 1, 2) deuteron target asymmetries, and the double polarization E-asymmetry are predicted and compared with available experimental data and other theoretical models. The effect of first-order rescattering is found to be much larger in spin asymmetries than in the unpolarized cross sections. It reaches on average about 40% in the tensor target and E asymmetries. Compared to the experimental data from CLAS Collaboration, sizable discrepancies are found. This is not the case for the linear photon asymmetry, for which a better comparison with the data from YerPhl Collaboration is obtained. (C) 2014 Elsevier Inc. All rights reserved.