Measurement with hadron beams at COMPASS

The physics program of the COMPASS experiment at CERN focuses on the investigation of the hadron structure and spectroscopy, using both leptonic and hadronic probes. The COMPASS experiment has collected so far mostly data with polarized muon beams of 160 GeV, but also a pilot data taking with negative hadron beams of 190 GeV has been successfully completed at the end of the 2004 run. The main physics objectives of this pilot run are the study of soft pion-nuclei interactions. The predictions of the Chiral Perturbation Theory for the electric and magnetic polarizabilities of the pion will be verified through the study of the Primakoff scattering of 190 GeV pions on thin lead targets. A sample corresponding to an integrated beam flux of more than 10$^{11}$ pions has been collected for this purpose, and an equivalent sample with the muon beam of 190 GeV has been collected in the same experimental conditions to correct possible systematic effects. In parallel to the polarizability measurements, first data have also been collected for the study of the diffractive production of exotic non-$q\bar{q}$ states. Such states, although predicted by QCD, still require a confirmation from the experimental side. This measurements are part of a wider research program, which includes the study of gluon-rich states produced in central proton-proton collisions, that will be addressed by the COMPASS experiment in the forthcoming years. The performances of the apparatus during the pilot COMPASS run with hadron beams will be presented, and the preliminary results of the analysis of the collected data will be discussed. The future perspectives of the proposed measurements will also be briefly outlined.