Measurement of the Magnitude and Phase ofρ−ωInterference inπ+ω−Photoproduction from Carbon

The reaction $\gamma +\mathrm{C}\to {\pi }^{+}+{\pi }^{-}+\mathrm{C}$ has been investigated in the invariant-mass region of the $\rho$ and $\omega$ mesons and shows distinct interference effects between the $\rho$ and $\omega$ contributions to the cross section. The experiment was performed at a mean photon energy of 4.2 GeV with 140 000 events. A phenomenological analysis of the data yields the result ${\Gamma }_{\omega \to 2\pi }={0.091}_{-0.025\mathrm{}}^{+0.031\mathrm{}}$ MeV/${\mathit{c}}^2$. The relative phase of the $\rho$ and $\omega$ terms in the amplitude is obtained and discussed.