Proposal of Experiment Pion double charge exchange on oxygen at J-PARC Sks Plus Spectrometer Group (J-PARC),

We propose to measure pion double charge exchange (DCX) cross sections on oxygen to investigate mechanisms of DCX at high energy. The Sks Plus Spectrometer has a unique possibility for detailed study of DCX in the most interesting energy range due to high intensity beams, available at J-PARC, very high momentum resolution, suffi-cient for observation of double isobar analoge transitions in nuclei and wide momentum acceptance, which is necessary for the inclusive DCX study. Above LAMPF energies these two processes are theoretically expected to be governed by different mechanisms of the “elastic ” (with π0 intermediate state) and “inelastic ” (with ππ intermediate state) two sequential pion-nucleon interactions. Exclusive DCX reactions, as predicted by the conventional mechanism equivalent to the Glauber model with the “elastic ” intermediate state (π0), rapidly drop above 0.55 GeV. Meanwhile, inclusive processes have relatively smooth energy dependence due to effects of “inelastic ” (mostly 2π) states. If observed, these different energy behaviors will be clear experimental evidence for inelastic inter-mediate transitions in hadron propagation through the nuclear matter. The beam energy of 1- 2 GeV is well suited for the experiment. Theoretically estimated decrease of the inclusive DCX cross section in this range is about 3 times within “inelastic ” mechanism. The cross section for DIAS transition on 18O(π+, π−)18Ne is expected on the level of 10−2μb/sr within ”elastic ” mechanism.