Neutral pion photoproduction has been measured from 550 to 1500 MeV with the GRAAL facility, located at the ESRF in Grenoble. Differential cross-section and beam asymmetry have been measured over a wide angular range. These high-precision data improve significantly the database for the beam asymmetry in the second and third resonance regions covering for the first time the energy domain 1100-1500 MeV. New partial-wave analyses including these data are presented for which the beam asymmetry brings crucial constraints.

Experimental results on the neutron detection efficiency of the GRAAL BGO calorimeter obtained from a study of gammap rarr pi +n reaction are reported. Pulse height spectra were measured for neutron energies from 80 to 650 MeV. A comparison of the experimental data with a GeanT-based simulation is presented

Differential cross sections and polarised photon beam asymmetries for eta, pi 0 and pi + photoproduction on the proton, produced by results cover wide angular and energy ranges of 40-170deg and 550-1496 MeV (707-1496 MeV for eta) respectively, and exhibit an unprecedented level of accuracy. The results are compared with predictions of several models

A polarised and tagged gammaoarrray beam is produced at GRAAL with energies ranging from 500 MeV up to 1500 MeV. Results of beam polarisation asymmetries and cross sections for the photoproduction of pseudoscalar mesons on the proton are presented. These very precise measurements cover the angular range 30deg-150deg, providing stringent constraints to theoretical models

The total photoabsorption cross section on a free proton was measured at the GRAAL facility in the energy range Egamma=600-1500 MeV. The large-aperture LAGR ANgammaE detector and a liquid hydrogen target were used in the experiment performed with a back-scattered Compton gamma beam. To improve the accuracy, two alternative methods were employed. First, a subtraction method of using empty- target measurements allowed the cross section sigma tot to be evaluated directly because of a low level of the electromagnetic background. Second, an algorithm for evaluating sigma tot on the basis of summing the dominating partial cross sections was developed. Experimental results obtained for sigma tot by the two methods are compared with existing data.

The features of the Graal experiment at ESRF are presented. The obtained results are discussed and future developments outlined. The Graal experiment started data taking in 1997. It was run for one year with the green laser line giving rise to a photon beam of maximum energy of 1100 MeV and for one year with UV multi-line and the corresponding gamma-ray beam of 1470 MeV maximum energy. Asymmetry data and cross sections have been produced for eta, pi 0 and pi + photoproduction channels providing, for these reactions, the most extended and coherent data base available until now. Future developments of the experiment will include the study of the same channels with deuteron target and the study of the photoreaction mechanism on the quasi-free neutron. The use of a polarised target of new concept will allow to access double polarisation observables for meson photoproduction on polarised proton and polarised neutron. Finally the increase in the maximum photon energy, up to 1.8 GeV will allow to study in details eta' photoproduction and to reach the threshold for scalar mesons production

Abstract Disintegration of 12 C nuclei by tagged photons of 700–1500 MeV energy at the GRAAL facility has been studied by means of the LAGRAN γ E detector with a wide angular acceptance. The energy and momentum distributions of produced neutrons and protons as well as their multiplicity distributions were measured and compared with corresponding distributions calculated with the RELDIS model based on the intranuclear cascade and Fermi break-up models. It was found that eight fragments are created on average once per about 100 disintegration events, while a complete fragmentation of 12 C into 12 nucleons is observed typically only once per 2000 events. Measured multiplicity distributions of produced fragments are well described by the model. The measured total photoabsorption cross section on 12 C in the same energy range is also reported.