Narrow Results

The pp→ppπ⁺π^- and pp→ppπ⁰π⁰ reactions have been measured at CELSIUS in the energy range T_p=775-1360 MeV using the WASA 4π detector. For T_p<1 GeV the data are in accordance with Roper excitation and σ correlations in the ππ system, respectively. For T_p>1 GeV they agree with ΔΔ excitation in the special configuration (ΔΔ)_0⁺. For the π⁰π⁰ channel an enhancement at low M_π⁰π⁰ masses is observed, which possibly points to Bose-Einstein correlations.

The pp→ppx(x=γγ, π⁰π⁰, π⁺π^-) reactions have been measured at CELSIUS in the energy range T_p=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 ppπ⁰π⁰ channel basically shows similar features, however, develops a peculiar enhancement at small invariant masses M_π⁰π⁰ - 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→³Hex (x=π⁰π⁰, π⁺π^-), where the observed π⁰π⁰ enhancements are still much larger. In the γγ channel a line at M_γγ=2m_π is observed. The possible nature of this line is discussed.