Hadron-Photon Interactions in COMPASS

The CERN COMPASS experiment will investigate hadron-photon interactions, to achieve a unique Primakoff Coulomb physics program based on hadron polarizability, hybrid mesons, chiral anomaly, and meson radiative transition studies. In COMPASS, pion (kaon) polarizabilities and radiative transitions will be measured via dedicated Primakoff effect reactions such as πγ → π ′ γ and πγ → M (meson). We will also study pionic and kaonic hybrid mesons in COMPASS by Primakoff production. We will also study the radiative transition of a pion to a low mass two-pion system, πγ → π ′ π, for a measure of the chiral anomaly amplitude F3π (characterizing γ → 3π). Our objectives are to determine new properties of hadrons and to provide important new tests of QCD chiral dynamics. The CERN COMPASS experiment use 50-280 GeV beams (μ, π, K, p) and a virtual photon target, and magnetic spectrometers and calorimeters to measure the complete kinematics of hadron-photon reactions. The COMPASS experiment is currently under construction, and scheduled in 2000 to begin data runs, with muons initially and hadrons following. The Primakoff program in COMPASS is approved as the first hadron physics program. We carry out simulation studies to optimize the beam, detector, trigger, and hardware/software for achieving high statistics data with low systematic uncertainties in this program. For kaon studies, our results will be the first ever. For pion studies, we will improve previous results by more than two orders of magnitude. We will implement special detectors and triggers for hadron-photon reactions. We will prepare the COMPASS hadron-photon Primakoff studies by setting up with muon-photon Primakoff tests. 1. Hadron-Photon Interactions: The COMPASS physics programs [1, 2] include studies of hadron-photon Primakoff interactions using 50-280 GeV/c negative beams (pions, kaons) and positive beams (pions, kaons, protons) together with a virtual photon target in dedicated data runs. Pion and kaon and proton polarizabilities, hybrid mesons, the chiral anomaly, and radiative transitions can be