ωρ0Interference Effect in Theπ+p→π+π−Δ++Interaction

Evidence for a destructive interference effect between the ${\ensuremath{\rho}}^{0}$ and $\ensuremath{\omega}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ amplitudes has been observed in the channel ${\ensuremath{\pi}}^{+}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\Delta}}^{++}$ at 3.7-4.0 GeV/c. On the assumption of complete coherence between the ${\ensuremath{\rho}}^{0}$ and $\ensuremath{\omega}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ amplitude in a subsample, discussed in the text, a branching ratio $\frac{(\ensuremath{\omega}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})}{(\ensuremath{\omega}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0})}=1.5%$ is obtained with a 95% confidence-level lower limit of 0.25%. The data do not lead to a significant upper limit. In terms of $\ensuremath{\delta}$, the off-diagonal element of the ${\ensuremath{\rho}}^{0}\ensuremath{\omega}$ mass-mixing matrix, these values are equivalent to $\ensuremath{\delta}=2.7$ MeV and a lower limit of 1.1 MeV. Under conditions stated in the text, a value $\ensuremath{\beta}=1.5\ifmmode\pm\else\textpm\fi{}0.3$ rad is obtained for the production phase of ${\ensuremath{\rho}}^{0}$ relative to $\ensuremath{\omega}$ in the channel studied.