Kj. Fransson

MEASUREMENT OF THE ω MESON POLARIZATION IN THE pd → 3He ω REACTION AT 1360 AND 1450 MeV

The tensor polarization of ω mesons produced in the pd → 3Heω reaction has been measured at two energies near threshold. The 3He nuclei were detected in coincidence with the π0π+π- or π0γ decay products of the ω. The ω mesons are found to be unpolarised, which is in complete contrast to the case of ϕ-meson production from the corresponding reaction pd → 3Heϕ. This brings into question the applicability of the Okubo-Zweig-Iizuka rule when comparing the production of vector mesons in low energy hadronic reactions.

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 Tp = 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 Tp > 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.