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ISSN - 03230465, Acta Physica Slovaca, 2006, vol. 56, p. 285-297

On the ππ production in free and in-medium NN-collisions: σ-Channel low-mass enhancement and πoπo/π +π--asymmetry

Bashkanov M., Skorodko T., Bargholtz C., Bogoslawsky D., Calén H., Cappellaro F., Clement H., Demiroérs L., Doroshkevich E., Ekström C., Fransson K., Geren L., Greiff J., Gustafsson L., Höistad B., Ivanov G., Jacewicz M., Jiganov E., Johansson T., Kaskulov M. M., Keleta S., Khakimova O., Koch I., Kren F., Kullander S., Kupśé A., Kuznetsov A., Lindberg K., Marciniewski P., Meier R., Morosov B., Oelert W., Pauly C., Petukhov Y., Povtorejko A., Ruber R. J M Y, Scobel W., Shafigullin R., Shwartz B., Sopov V., Stepaniak J., Tegner P. E., Tchernyshev V., Thörngren-Engblom P., Tikhomirov V., Turowiecki A., Wagner G. J., Wolke M., Yamamoto A., Zabierowski J., Zartova I., Zlomanczuk J.

The pp → NN ππ and pd → 3He ππ reactions have been measured exclusively at CELSIUS using the WASA 4π detector with pellet target system. With regard to the first reaction measurements have been conducted from the near-threshold region up to Tp = 1.45 GeV. For the double-pionic fusion to 3He data have been taken at Tp = 0.893 GeV, where the maximum of the so-called ABC effect is expected. For the 3He case a huge low-mass enhancement is observed in the πoπo invariant mass Mπo πo, whereas only a moderate low-mass enhancement is seen in M π+π-. The pp → ppππ reaction in the near threshold region can be well described by Roper excitation and chiral dynamics, however, at higher energies, in the ΔΔ © Institute of Physics, SAS, Bratislava, Slovakia.