Pion absorption in 1 GeV/c region

As for the absorption of π mesons, according to the law of conservation of energy and momentum, the absorption by one nucleon is prohibited, and always two nucleons or more take part. π meson absorption experiment has been carried out so far in Δ region and below it. The change of the absorption mechanism in GeV region is interesting, but the other experiment than that with deuteron target has not been carried out. By using 4He as target nuclei, the reaction of absorbing π mesons in two nucleons and emitting those two nucleons, namely the absorption cross section of 4He(π+,pp)(π+,pn) was measured. By measuring simultaneously these two channels, the knowledge on the isospin dependence of two nucleons that absorbed π mesons was obtained, and the comparison with existing deuteron absorption cross section was carried out. The experiment was carried out at the 12 GeV proton synchrotron in the National Laboratory for High Energy Physics. The simultaneous measurement was made with a spectrometer and a TOF counter. The correlation of the momentum of forward emitted protons and the velocity of backward emitted nucleons is shown. Also the distribution of missing mass and the angular distribution of forward emitted nucleons are shown. As for these experimental results, the analysis was carried out. (K.I.)