BEAM ASYMMETRY Sigma OF THE pi(-) PHOTOPRODUCTION OFF NEUTRON

We present the analysis of data performed in order to identify the events of the gamma + n -> pi(-) + p reaction obtained by bombarding a liquid Deuterium target with a polarised. beam of 0.55-1.5 GeV at the Graal-experiment. We show the effect of different kinematic and hardware constraints used to reduce the contamination coming from the concurrent reaction channels. By the simulation we estimate the contamination degree due to the other reaction channels so we can test the reliability of our method. We describe a new three-dimensional cut based on the Fermi momentum reconstruction and its effect on the suppression of the concurrent double charged pion photoproduction. We present the preliminary beam asymmetry Sigma of the pi(-) fotoproduction off quasi-free neutron up to about theta(c.m.), (pi-) = 165 degrees together with some theoretical multipolar analysis. For a comparison we also report the data present in literature on the same reaction for E-gamma -850-1740 MeV and theta(c.m.), (pi-) <= 105 degrees.