Analysis of rho-omega interference in the pion form-factor

The formalism underlying the analysis of e+e− → π+π− in the ϱ-ω interference region is carefully revisited. We show that the standard neglect of the pure I = 0 omega, ωI, “direct” coupling to ππ is not valid, and extract those combinations of the direct coupling and ϱ-ω mixing allowed by experiment. The latter is shown to be only very weakly constrained by experiment, and we conclude that data from the e+e− → π+π− interference region cannot be used to fix the value of ϱ-ω mixing in a model-independent way unless the errors on the experimental phase can be significantly reduced. Certain other modifications of the usual formalism necessitated by the unavoidable momentum-dependence of ϱ-ω mixing are also discussed.