Photoproduction experiments with polarized HD targets

Within the French-Italian GRAAL collaboration, we have constructed a Polarized HD Target Factory (HYDILE), implanted at IPN Orsay. This project is very similar to the SPHICE one existing at BNL, and developed within the LEGS Spill Collaboration. The expected properties of the HD targets and the results already obtained for the polarization of HD samples at Orsay and BNL are given. New possibilities to measure polarization observables oil the proton, the neutron and the deuteron are now opened. Most simple and double polarization measurements for the photoproduction of the low mass pseudoscalar and vector mesons could be performed, by using the high polarization (linear or circular) of the backscattered photon beams and the large effective polarization (longitudinal or tranverse) of the target, resulting essentially, from the good dilution factor. Polarized total cross sections concerning the isovector Drell-Hearn Gerasimov Sum Rule related to the proton neutron difference, could be measured with minimum systematic uncertainties: the target containing both polarized protons and neutrons. By using the available polarized photon beams from LEGS, GRAAL and Spring-8, measurements could be done from the pi meson threshold up to 2.5 Gev, where the pi meson photoproduction cross section is close to its maximum value. Typical examples are given for GRAAL and Spring-8.