Dispersive representation of the pion vector form factor in $\tau\to\pi\pi\nu_\tau$ decays

TL;DR

This paper develops a dispersive model for the pion vector form factor in tau decays, fitting it to Belle data and ensuring consistency with fundamental symmetries, to improve the understanding of hadronic tau decay spectra.

Contribution

It introduces a dispersive representation of the pion vector form factor that incorporates chiral symmetry, analyticity, and unitarity constraints, fitted to high-precision experimental data.

Findings

Good fit to Belle tau decay data up to 1.5 GeV^2

Determination of low energy pion observables

Framework for implementing in TAUOLA hadronic currents

Abstract

We propose a dispersive representation of the charged pion vector form factor that is consistent with chiral symmetry and fulfills the constraints imposed by analyticity and unitarity. Unknown parameters are fitted to the very precise data on $\tau^-\to\pi^-\pi^0\nu_\tau$ decays obtained by Belle, leading to a good description of the corresponding spectral function up to a $\pi\pi$ squared invariant mass $s\simeq 1.5$ GeV$^2$. We discuss the effect of isospin corrections, and obtain the values of low energy observables. For larger values of $s$, this representation is complemented with a phenomenological description to allow its implementation in the new TAUOLA hadronic currents.