The branching ratio $omega to pi^+pi^-$ revisited


Abstract in English

We analyze the most recent data for the pion vector form factor in the timelike region, employing a model-independent approach based on dispersion theory. We confirm earlier observations about the inconsistency of different modern high-precision data sets. Excluding the BaBar data, we find an updated value for the isospin-violating branching ratio $mathcal{B}(omega to pi^+pi^-) = (1.46pm 0.08) times 10^{-2}$. As a side result, we also extract an improved value for the pion vector or charge radius, $sqrt{langle r_V^2rangle} = 0.6603(5)(4)text{fm}$, where the first uncertainty is statistical as derived from the fit, while the second estimates the possible size of nonuniversal radiative corrections. In addition, we demonstrate that modern high-quality data for the decay $eta to pi^+pi^-gamma$ will allow for an even improved determination of the transition strength $omegatopi^+pi^-$.

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