Abstract
The QCD coupling αs is determined at NLO*+NMLLA accuracy from the comparison of experimental jet data to theoretical predictions of the energy-evolution of the parton-to-hadron fragmentation function moments (multiplicity, peak, width, skewness) at low fractional hadron momentum z. From the existing e+e− and e±p jet data, we obtain αs(mZ2)=0.1195±0.0021(exp)−0.0+0.0015(scale) at the Z mass. The uncertainties of the extracted αs value are discussed.
Highlights
In the chiral limit, the theory of the strong interaction –quantum chromodynamics (QCD)–has a single fundamental parameter: its coupling αs which decreases logarithmically with increasing energy scale Q, i.e. αs ∝ln(Q2/Λ2 ), starting from a value QCDΛQCD ≈ 0.2 GeV where the perturbatively-defined coupling diverges
In Ref. [5] we have presented a novel extraction of αs from the energy evolution of the first four moments of the parton-to-hadron fragmentation functions (FFs) including, for the first time, resummations of higher-order (NNLL or NMLLA) logarithms and NLO running-coupling corrections
hump-backed plateau” (HBP) moments which depend only on ΛQCD. Such an approach is justified for infrared-safe observables by the “local parton-hadron duality” hypothesis which states that the distribution of partons in jets is identical to that of the final hadrons
Summary
In the chiral (massless quark) limit, the theory of the strong interaction –quantum chromodynamics (QCD)–. [3]) to try to measure ΛQCD (or, equivalently, αs) using partonto-hadron fragmentation functions (FFs) in the region of low fractional momenta z = ph/pparton via the Modified Leading Logarithmic Approximation (MLLA) [4] which resums the soft and collinear singularities present in this region of phase-space These older calculations were limited to LO approximations with a number of simplifying assumptions: (i) ad hoc cuts in the experimental distributions, (ii) simple fits in a restricted FF range, (iii) number of quark-flavours fixed to N f = 3, and (iv) use of only one or two FF moments (Gaussian approximation). S= 3.8 GeV [ZEUS'95] s= 5.3 GeV [ZEUS'95] s= 7.3 GeV [ZEUS'95] s= 10.4 GeV [ZEUS'95]
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