/ Experiment-Nucl arXiv:0906.3087

Two-Pion Production in Proton-Proton Collisions: Experimental Total Cross Sections and their Isospin Decomposition

Skorodko, T. ; Bashkanov, M. ; Bogoslawsky, D. ; Calen, H. ; Clement, H. ; Doroshkevich, E. ; Demiroers, L. ; Ekstrom, C. ; Fransson, K. ; Gustafsson, L. ; Hoistad, B. ; Ivanov, G. ; Jacewicz, M. ; Jiganov, E. ; Johansson, T. ; Khakimova, O. ; Keleta, S. ; Koch, I. ; Kren, F. ; Kullander, S. ; Kupsc, A. ; Marciniewski, P. ; Meier, R. ; Morosov, B. ; Pauly, C.

Published in: Phys.Lett.
Year: 2009
Vol.: B679
Page No: 30-35
Pages: 9

Abstract: The two-pion production in pp-collisions has been investigated at CELSIUS in exclusive measurements from threshold up to $T_p$ = 1.36 GeV. Total and differential cross sections have been obtained for the channels $pn\pi^+\pi^0$, $pp\pi^+\pi^-$, $pp\pi^0\pi^0$ and also $nn\pi^+\pi^+$. For intermediate incident energies $T_p >$ 1 GeV, i.e. in the region which is beyond the Roper excitation but at the onset of $\Delta\Delta$ excitation, the total $pp\pi^0\pi^0$ cross section falls behind theoretical predictions by as much as an order of magnitude near 1.2 GeV, whereas the $nn\pi^+\pi^+$ cross section is a factor of five larger than predicted. An isospin decompostion of the total cross sections exhibits a s-channel-like energy dependence in the region of the Roper excitation as well as a significant contribution of an isospin 3/2 resonance other than the $\Delta(1232)$. As possible candidates the $\Delta(1600)$ and the $\Delta(1700)$ are discussed.

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