Exclusive Measurement of the $pp\to nn{\pi }^{+}{\pi }^{+}$ Reaction at 1.1 GeV

Abstract

First exclusive data for the $pp\to nn{\pi }^{+}{\pi }^{+}$ reaction have been obtained at CELSIUS with the WASA detector setup at a beam energy of $T_p$ = 1.1 GeV. Total and differential cross sections disagree with theoretical calculations, which predict the $\Delta \Delta$ excitation to be the dominant process at this beam energy. Instead the data require the excitation of a higher-lying $\Delta$ state, most likely the $\Delta (1600)$, to be the leading process.