Measurement of total cross-section of antiproton-proton reaction in the momentum range between 400 and 700 MeV/c

Low momentum antiproton-proton experiment was performed at the K3 beam channel of KEK. The primary purpose of this experiment is to investigate the famous S (1936) resonance, which is a candidate of a baryonium, an exotic meson composed of two quarks and two antiquarks. A stable hadron is called exotic if its quark configuration is other than quark-antiquark or quark-quark-quark. The existence of the baryoniums was first predicted by duality argument. A good deal of experimental effort has been made in search of baryoniums. Experiments are classified into two categories. The one is resonance search in antiproton-proton interaction and the other is bump hunting in production experiments. Once the S resonance seemed to be established, but at present, the very existence of the S resonance has become a burning question. The present experimental method is the total cross section measurement known as the transmission method, where the particles transmitted to a target without interacting in it are counted. The possible narrow structure (in particular, the S resonance) in the antiproton-proton total cross section in the momentum range between 400 and 700 MeV/c was investigated. Multiwire proportional chambers and a magnetic spectrometer were used. The preliminary result is consistent with the nonexistence of the S resonance. (Kato, T.)