Resonant behavior of the $pp \to \{pp\}_s \pi^0$ reaction at the energy $\sqrt{s}$ = 2.65 GeV

Abstract

We report on measurements of the differential cross section $d\sigma/d\Omega$ in the energy region of $\sqrt{s}$ = 2.5-2.9 GeV of the reaction $pp \to \{pp\}_s \pi^0$ where $\{pp\}_s$ is a $^1\!S_0$ proton pair. The experiment has been performed with the ANKE spectrometer at COSY-J\"ulich. The data reveal a peak in the energy dependence of the forward $\{pp\}_s$ differential cross section at the energy $\sqrt{s}$ = 2.65 GeV with the width $\Gamma$ = 0.26 GeV, and also the cross section slope changes its sign in the region of the observed peak. This is an indication for the excitation of a new $D(2650)$ resonant state, that may be a dibaryon resonance system consisting of two excited baryons $\Delta(1232)$ and $N^*(1440)$.