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ISSN - 0217751X, International Journal of Modern Physics A, 2005, vol. 20, p. 1747-1752

Two-pion production, γγ line and aspects of σ meson, Bose-Einstein correlations and isospin breaking

Clement H., Bashkanov M., Doroshkevich E., Kaskulov M., Khakimova O., Kren F., Meier R., Skorodko T., Wagner G. J., Bogoslawsky D., Ivanov G., Jiganov E., Kuznetsov A., Morosow B., Petukhov Y., Povtorejko A., Tikhomirov V., Calén H., Ekström C., Fransson K., Kupść A., Marciniewski P., Ruber R. J M Y, Cappellano F., Gustafsson L., Höistad B., Jacewicz M., Johansson T., Keleta S., Koch I., Kullander S., Thörngren Engblom P., Wiedner U., Wolke M., Zlomanczuk J., Demiroers L., Greiff J., Pauly C., Scobel W., Oelert W., Shwartz B., Sopov V., Tchernyshev V., Stepaniak J., Zabierowski J., Turowiecki A., Yamamoto A.

The pp → ppx(x = γγ, π0π0, π+π-) reactions have been measured at CELSIUS in the energy range Tp = 775 - 1360 MeV using the WASA 4π detector with hydrogen pellet target. Close to threshold the ppπ+π - data are in accordance with the Roper resonance concept and/or a dynamic formation of the σ meson. At higher energies the formation of the ΔΔ system becomes increasingly dominant. The ppπ0π 0 channel basically shows similar features, however, develops a peculiar enhancement at small invariant masses Mπ0π0 - in resemblance of Bose-Einstein correlations. Alternatively, the enhancement could be also indicative of a (dynamic) isospin breaking due to ππ rescattering in the σ channel. The latter is favored by the results on pd →3He x (x = π0π0, π+π-), where the observed π0π 0 enhancements are still much larger. In the γγ channel a line at Mγγ = 2mπ is observed. The possible nature of this line is discussed. © World Scientific Publishing Company.