Coherent pi(0) photoproduction from He-4

Differential cross sections and beam asymmetries for coherent pi(0) photopr oduction from He-4 in the Delta energy-range have been measured with high s tatistical and systematic precision using both decay photons for identifyin g the process. The experiment was performed at the MAinz MIcrotron using th e TAPS photon spectrometer and the Glasgow/Mainz tagged photon facility. Th e differential cross sections are in excellent agreement with predictions b ased on the DWIA if an appropriate parametrization of the Delta-nuclear int eraction is applied. The beam asymmetries are interpreted in terms of degre es of linear polarization of collimated coherent bremsstrahlung. The expect ed increase of the degree of linear polarization with decreasing collimatio n angle is confirmed. Agreement with calculations is obtained on a few-perc ent level of precision in the maxima of the coherent peaks. (C) 1999 Elsevi er Science B.V. All rights reserved.