Accounting for correlations in the $ωπ$ spectral function and its implication on the leading model dependent contribution to the $τ^- \to π^-π^0 ν_τγ$ decay

Abstract

The $ωπ$ spectral function, measured in the decay $τ^- \to π^-ων_τ$ by the CLEO Collaboration, is described in the vector meson dominance approach. We sample the parameter space using a Metropolis Monte-Carlo algorithm and generate a set of parameters of the corresponding form factor, explicitly accounting for the correlation among them. We show the improvement in the uncertainty region of the spectral function with respect to neglecting correlations. We test the conserved vector current hypothesis by showing the agreement of the spectral function with the expected from the measurement of the cross section of $e^+e^- \to ωπ$ by the SND experiment, and the consistency of the branching ratio of the $τ^- \to π^-ων_τ$ decay with the value reported by the Particle Data Group. As an application, we consider the $ω$-channel of the $τ^- \to π^-π^0ν_τγ$ process, the leading model dependent contribution in the vector meson dominance approach. We compute the contribution to the long distance electromagnetic correction function $G_\text{EM}(t)$, of the pure $ω$-channel and its interference with the structure independent part. We show that the uncertainties, using the set of correlated parameters, are largely reduced with respect to neglecting correlations. The implication on the isospin symmetry breaking correction to the muon magnetic dipole moment estimation from tau data is found to be consistent with previous results but with improved precision.