Updated determination of ${\alpha }_s(m_{\tau }^2)$ from tau decays

Abstract

Using the most recent release of the ALEPH $\tau$ decay data, we present a very detailed phenomenological update of the ${\alpha }_s(m_{\tau }^2)$ determination. We have exploited the sensitivity to the strong coupling in many different ways, exploring several complementary methodologies. All determinations turn out to be in excellent agreement, allowing us to extract a very reliable value of the strong coupling. We find ${\alpha }_s^{(n_f=3)}(m_{\tau }^2)=0.328\pm 0.012$ which implies ${\alpha }_s^{(n_f=5)}(M_Z^2)=0.1197\pm 0.0014$. We critically revise previous work, and point out the problems flawing some recent analyses which claim slightly smaller values.

Comments: Invited contribution to the MITP workshop on Determination of the Fundamental Parameters in QCD (Mainz, 7-11 March 2016). 15 pages, 8 figures