We give a factorization formula for the e + e − thrust distribution dσ/dτ with τ = 1 − T based on soft-collinear effective theory. The result is applicable for all τ , i.e. in the peak, tail, and fartail regions. The formula includes O(α 3 s ) fixed-order QCD results, resummation of singular partonic α j s ln k (τ )/τ terms with N 3 LL accuracy, hadronization effects from fitting a universal nonperturbative soft function defined in field theory, bottom quark mass effects, QED corrections, and the dominant top mass dependent terms from the axial anomaly. We do not rely on Monte Carlo generators to determine nonperturbative effects since they are not compatible with higher order perturbative analyses. Instead our treatment is based on fitting nonperturbative matrix elements in field theory, which are moments Ωi of a nonperturbative soft function. We present a global analysis of all available thrust data measured at center-of-mass energies Q = 35 to 207 GeV in the tail region, where a two parameter fit to αs(mZ) and the first moment Ω1 suffices. We use a short distance scheme to define Ω1, called the R-gap scheme, thus ensuring that the perturbative dσ/dτ does not suffer from an O(ΛQCD) renormalon ambiguity. We find αs(mZ) = 0.1135 ± (0.0002)expt ± (0.0005) hadr ± (0.0009)pert, with χ 2 /dof = 0.91, where the displayed 1-sigma errors are the total experimental error, the hadronization uncertainty, and the perturbative theory uncertainty, respectively. The hadronization uncertainty in αs is significantly decreased compared to earlier analyses by our two parameter fit, which determines Ω1 = 0.323 GeV with 16% uncertainty.

We consider cumulant moments (cumulants) of the thrust distribution using predictions of the full spectrum for thrust including O(α 3 s ) fixed order results, resummation of singular N 3 LL logarithmic contributions, and a class of leading power corrections in a renormalon-free scheme. From a global fit to the first thrust moment we extract the strong coupling and the leading power correction matrix element Ω1. We obtain αs(mZ) = 0.1140 ± (0.0004)exp ± (0.0013) hadr ± (0.0007)pert, where the 1-σ uncertainties are experimental, from hadronization (related to Ω1) and perturbative, respectively, and Ω1 = 0.377 ± (0.044)exp ± (0.039)pert GeV. The n-th thrust cumulants for n ≥ 2 are completely insensitive to Ω1, and therefore a good instrument for extracting information on higher order power corrections, Ω ′ n /Q n , from moment data. We find (Ω ′ 2 ) 1/2 = 0.74 ± (0.11)exp ± (0.09)pert GeV.

We present a new prescription for the resummation of the divergent series of perturbative corrections, due to soft gluon emission, to hard processes near threshold in perturbative QCD (threshold resummation). This prescription is based on Borel resummation, and contrary to the commonly used minimal prescription, it does not introduce a dependence of resummed physical observables on the kinematically unaccessible x->0 region of parton distributions. We compare results for resummed deep-inelastic scattering obtained using the Borel prescription and the minimal prescription and exploit the comparison to discuss the ambiguities related to the resummation procedure.Comment: 15 pages, 3 figures. Final version, to be published in Phys. Lett. B. Several typos corrected (in particular eqs 26,41,53); fig. 3 adde

We provide a determination of the Gottfried sum from all available data, based on a neural network parametrization of the nonsinglet structure function F2. We find SG = 0.244 ± 0.045, closer to the quark model expectation SG = 1 3 than previous results. We show that the uncertainty from the small x region is somewhat underestimated in previous determinations.

From soft-collinear effective theory one can derive a factorization formula for the e + e − thrust distribution dσ /dτ with τ = 1 − T that is applicable for all τ. The formula accommodates available O(α 3 s ) fixed-order QCD results, resummation of logarithms at N 3 LL order, a universal nonperturbative soft function for hadronization effects, factorization of nonperturbative effects in subleading power contributions, bottom mass effects and QED corrections. We emphasize that the use of Monte Carlos to estimate hadronization effects is not compatible with high-precision, high-order analyses. We present a global analysis of all available e + e − thrust data measured at Q = 35 to 207 GeV in the tail region, where a two-parameter fit can be carried out for α s (m Z ) and Ω 1 , the first moment of the soft function. To obtain small theoretical errors it is essential to define Ω 1 in a short-distance scheme, free of an O(Λ QCD ) renormalon ambiguity. We find α s (m Z ) = 0.1135 ± (0.0002) expt ± (0.0005) Ω 1 ± (0.0009) pert with χ 2 /dof = 0.9.