Thrust atN3LLwith power corrections and a precision global fit forαs(mZ)

Abstract

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.

Drell-Yan production atNNLL′+NNLOmatched to parton showers

“…For the transverse momentum of the vector boson and the related ϕ Ã distribution between the leptons, our default settings with α s ðM Z Þ ¼ 0.118 predict a somewhat harder spectrum. We observe a much better agreement with the data when using a lower value of the strong coupling constant α s ðM Z Þ ¼ 0.1135, as was obtained from fits of N 3 LL 0 resummed calculations of event shapes to LEP data [37][38][39][40]. The same was also observed for resummation observables in our e þ e − results in Ref.…”

Determination ofαsfrom the QCD static energy: An update

“…[45,46]; from thrust in e + e − collisions in Refs. [4,47]; the recent H1 re-analysis of Ref. [48]; and the PDF-fit ABM13 result of Ref.…”

“…[3] with the value obtained from analyses of the event-shape variable thrust in e + − e − collisions of Ref. [4]. Disagreements like that question, to some extent, if the uncertainty quoted in the world average really reflects our current understanding of the value of α s .…”

Medium-induced parton splitting kernels from Soft Collinear Effective Theory with Glauber gluons

“…In particular, Soft Collinear Effective Theory [25][26][27][28] (SCET) is an effective theory for QCD that describes the dynamics of highly energetic partons. It has been successfully applied to improve the theoretical accuracy in the evaluation of high energy cross sections at lepton [29]- [32] and hadron colliders [33]- [35].…”