The strong coupling from hadronic $\tau$-decay data including $\tau\to\pi^-\pi^0\nu_\tau$ from Belle

TL;DR

This paper incorporates Belle's high-statistics $ au o ext{pi}^- ext{pi}^0 u_ au$ data into the construction of a comprehensive non-strange vector spectral function, leading to a new, precise determination of the strong coupling constant $oldsymbol{ extalpha_s}$ at the $Z$ mass scale.

Contribution

It introduces the first inclusion of Belle $ au$ decay data into the spectral function, refining the $ extalpha_s$ measurement using finite-energy sum rules.

Findings

New $ extalpha_s(m_Z^2)=0.1159(14)$ obtained

Updated spectral function with Belle data

Shifted $ extalpha_s$ value due to decay mode updates

Abstract

In previous work we have combined the $\pi^-\pi^0$, $2\pi^-\pi^+\pi^0$ and $\pi^-3\pi^0$ spectral data obtained from hadronic $\tau$ decays measured by the ALEPH and OPAL experiments, together with electroproduction data for several of the subleading hadronic modes and BaBar data for the $K\bar{K}$ mode to construct an inclusive non-strange vector spectral function entirely based on experimental data, with no Monte-Carlo generated input. In this paper, we include, for the first time, the Belle $\tau\to\pi^-\pi^0\nu_\tau$ high-statistics decay data to construct a new inclusive non-strange vector spectral function that combines more of the world's available data. As no Belle data are at present available for the two $4\pi$ modes, this requires a revised data analysis in comparison with our previous work. From the resulting new spectral function, we obtain a new determination of the strong coupling, $\alpha_s$, using our previously developed strategy based on finite-energy sum rules. We find, at the $Z$ mass scale, $\alpha_s(m_Z^2)=0.1159(14)$. We discuss the smaller central value and larger error of our new result compared to our previous result, showing the shifts to be due mainly to significant changes in updated HFLAV results for the $\pi^-3\pi^0$ decay mode.