ISSN - 0217751X, International Journal of Modern Physics A, 2009, vol. 24, p. 561-563

The pp → dπ+π0 reaction - A case of δδ excitation without ABC-effect

Kren F., Bashkanov M., Bogoslowsky D., CalÉn H., Clement H., EkstrÖm C., Fransson K., Gustafsson L., HÖistad B., Ivanov G., Jacewicz M., Jiganov E., Johansson T., Keleta S., Khakimova O., Koch I., Kullander S., Kupać A., Kuznetsov A., Marciniewski P., Meier R., Morosov B., Pauly C., Petterson H., Petukhov Y., Povtorejko A., Ruber R. J M Y, SchÖnning K., Scobel W., Shwartz B., Skorodko T., Sopov V., Stepaniak J., Tegner P. E., ThÖrngren-Engblom P., Tikhomirov V., Turowiecki A., Wagner G. J., Wolke M., Yamamoto A., Zabierowski J., Złomanćzuk J.

The ABC effect, a low-mass enhancement in the invariant ππ mass, is observed in double-pionic fusion reactions leading to a bound nuclear system in the final state. From previous measurements there have been indications that this phenomenon is resctricted to the σ channel of the ππ system. With exclusive measurements of the pp → dπ+π0 reaction at Tp = 1.1 GeV we demonstrate that, indeed, the ABC effect does not occur in the vector-isovector ππ channel (ρ channel) despite the fact that the δδ excitation is oberved to be the dominant reaction process. We also show that this reaction is well described by a t-channel δδ excitation with the subsequent decay into the vector-isovector ππ channel given by the ρ channel operator. © 2009 World Scientific Publishing Company.