Updated determination of αs(mτ2) from τ decays

Abstract

Using the most recent release of the ALEPH τ decay data, we present a very detailed phenomenological update of the αs(m 2 τ ) 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 αZ ) = 0.1197 ± 0.0014. We critically revise previous work, and point out the problems flawing some recent analyses which claim slightly smaller values.

Extraction of the strong coupling αs(mZ) from a combined NNLO analysis of inclusive electroweak boson cross sections at hadron colliders

“…This final extraction is fully consistent with the PDG world average, and has an overall uncertainty that is better than that of other recent determinations at this level of (NNLO) theoretical accuracy, such as those from EW precision fits [46], and tt cross sections [29,47]. In terms of precision, our determination compares well with the α s (m Z ) = 0.1191 ± 0.0018 value extracted from the theoretical analysis of τ lepton hadronic decays, which has an uncertainty of ∼1.5% [30,48,49].…”

Up- and down-quark masses from QCD sum rules

“…4. Potential, in principle unknown [28]- [29], duality violations are expected to be quenched above s 0 ≈ 3.0 GeV 2 , the region where the result is obtained.…”

Precision physics with inclusive QCD processes

“…The ALEPH analysis is based on the weights ( ) = (1− ) 2+ (1+2 ) [172], which incorporate the phase-space and spin-1 factors in (61) so that one can directly use the measured distribution. A more complete phenomenological analysis of the same experimental data [170,179] has recently investigated the stability of the results under changes of the chosen weights and has explored a large variety of alternative methodologies, including the dependence on the upper integration limit 0 [145,180,181] that was fixed at 2 in [171]. The most reliable determinations, summarized in table 3, are extracted with the weights ( ), ̂ ( ) = (1− ) 2+ , (2, ) ( ) = 1−( +2) +1 +( +1) +2 and (1, ) ( ) = (1− +1 ) e − .…”

“…Although the OPE is not valid in the real axis and the absence of weighting makes the low-energy integral up to ̂ 0 very exposed to uncontrolled effects, specially at such low ̂ 0 , a quite reasonable value of is extracted: ( 2 ) = 0.301 ± 0.012. 9 The uncertainties are however, largely underestimated, since the fitted coupling strongly depends on the chosen value of ̂ 0 and the assumed spectral function ansatz; small variations of the adopted choices lead to fluctuations larger than 3 [170,179,185]. The large correlations among all fitted quantities convert into an additional effective-model parameter, incorporating unaccounted systematics.…”