Abstract
The moments of the single inclusive momentum distribution of hadrons in QCD jets, are studied in the next-to-modified-leading-log approximation (NMLLA) including next-to-leading-order (NLO) corrections to the alpha_s strong coupling. The evolution equations are solved using a distorted Gaussian parametrisation, which successfully reproduces the spectrum of charged hadrons of jets measured in e+e- collisions. The energy dependencies of the maximum peak, multiplicity, width, kurtosis and skewness of the jet hadron distribution are computed analytically. Comparisons of all the existing jet data measured in e+e- collisions in the range sqrt(s)~2-200 GeV to the NMLLA+NLO* predictions allow one to extract a value of the QCD parameter Lambda_QCD, and associated two-loop coupling constant at the Z resonance alpha_s(m_Z^2)= 0.1195 +/- 0.0022, in excellent numerical agreement with the current world average obtained using other methods.
Highlights
QCD jets, are studied in the next-to-modified-leading-log approximation (NMLLA) including next-to-leading-order (NLO) corrections to the αs strong coupling
Comparisons of 2–200 GeV to the all the existing jet data NMLLA+NLO∗ predictions allow one to extract a value of the QCD parameter ΛQCD, and associated two-loop coupling constant at the resonance αs
Varying meff from zero to 0.32 GeV yields differences in the extracted ΛQCD parameter below ±0.5% for the ξmax fits and below ±2% for the other components, which indicate the robustness of our NMLLA+NLO∗ calculations for the limiting-spectrum distorted Gaussian (DG) with respect to finitemass effects if a wide enough range of charged-hadron and parent-parton energies are considered in the evolution fit
Summary
The fragmentation function of a parton a splitting into partons b and c satisfies the following system of evolution equations [4,5,6] as a function of the variables defined in figure 1:. In [23], only the first term of this expression was provided, the subleading contribution given here is new This NMLLA+NLO∗ correction to eq (3.25) increases the skewness of the distribution, while for increasing λ it should decrease again, revealing two competing effects. The final expression of the DG parametrisation of the single inclusive distribution of soft hadrons inside gluon and quark jets, eq (3.10), can be obtained summing all its individually-derived NMLLA+NLO∗-resummed components: the mean multiplicity N (Y, λ) eq (3.15), the mean peak position ξ(Y, λ) eq (3.18), the dispersion σ(Y, λ) eq (3.23), the skewness eq s(Y, λ) (3.25), and kurtosis k(Y, λ) eq (3.27). Energy conservation plays a more important role in the hard fragmentation region x ∼ 1 (ξ ∼ 0), where the NMLLA+NLO∗ DG is somewhat suppressed compared with the MLLA DG
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