Strong coupling from hadronic tau decays

by Martin Beneke (Aachen, CERN)

Thursday 22 Jan 2009, 10:00 → 11:00 Europe/Zurich

1/1-025 (CERN)

Hadronic tau decays provide one of the most accurate determinations of alpha_s. However, different ways of resumming the perturbative series with the renormalisation group -- fixed-order (FOPT) vs. contour-improved perturbation theory (CIPT) -- lead to a systematic difference that becomes more pronounced as higher orders in the perturbative expansion are added. On the basis of theoretical constraints on the large-order behaviour of the perturbative expansion originating from the operator product expansion and the renormalisation group, I investigate under which circumstances one or the other approach provides a better approximation to the true result. I argue that FOPT is preferred and obtain alpha_s(M_Z) = 0.1180 \pm 0.0008, lower than previous values obtained from tau decays, but in agreement with other determinatons.