Two-Pion Production in Proton-Proton Collisions.

A program to measure the two-pion production in nucleon-nucleon collisions exclusively and in all channels from threshold up to T_p = 1360 MeV has been started at CELSIUS-WASA. First preliminary results for ppπ+π¯ and ppπ⁰π⁰ channels are presented. In the near-threshold region they are consistent with a dominance of the Roper excitation and its successive decay into Nσ and Δπ channels. At energies T_p > 1 GeV we observe a very different behavior, which is at variance with theoretical predictions. At COSY-TOF exclusive measurements of the pp → ppπ+π¯ reaction have been carried out with polarized beam. Preliminary results show non-zero analyzing powers which point to a sizeable admixture of l ≠ 0 partial waves indicating possibly an influence of the ρ-channel. [ABSTRACT FROM AUTHOR]