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Stefan Kluth

Publications and source records attributed to Stefan Kluth.

26 records · Page 2Linked to original sources
arXiv2008

Hemisphere Soft Function at O(alpha_s^2) for Dijet Production in e+e- Annihilation

We determine the O(alpha_s^2) corrections to the partonic hemisphere soft function relevant for thrust and jet mass distributions in e+e- annihilation in the dijet limit. In this limit the distributions can be described by a factorization theorem that sums large logarithmic terms and separates perturbative from nonperturbative effects. Using the known O(alpha_s^2) contributions of the jet functions and the hard coefficients in the factorization theorem, constraints from renormalization group evolution and nonabelian exponentiation, and results from numerical integration of O(alpha_s^2) QCD matrix elements, the O(alpha_s^2) corrections of the soft function can be determined unambiguously. We study the impact of subtracting contributions related to the O(Lambda_QCD) renormalon in the partonic threshold using the soft function gap proposed recently by Hoang and Stewart, and we discuss the importance to account for the renormalization group evolution of the gap parameter. As a byproduct we also present the previously unknown next-to-next-to-leading logarithmic anomalous dimensions for the hard coefficient that appear in the factorization theorem for the double differential invariant mass distribution for heavy quark pair production at high energies in the resonance region proven by Fleming etal.

hep-ph↗
arXiv2007

α_S from LEP

Recent results on measurements of the strong coupling $α_S$ from LEP are reported. These include analyses of the 4-jet rate using the Durham or Cambridge algorithm, of hadronic $Z^0$ decays with hard final state photon radiation, of scaling violations of the fragmentation function, of the longitudinal cross section, of the $Z^0$ lineshape and of hadronic $τ$ lepton decays.

hep-ex↗
arXiv2006

Power Corrections in Electron-Positron Annihilation: Experimental Review

Experimental studies of power corrections with e+e- data are reviewed. An overview of the available data for jet and event shape observables is given and recent analyses based on the Dokshitzer-Marchesini-Webber (DMW) model of power corrections are summarised. The studies involve both distributions of the observables and their mean values. The agreement between perturbative QCD combined with DMW power corrections and the data is generally good, and the few exceptions are discussed. The use of low energy data sets highlights deficiencies in the existing calculations for some observables. A study of the finiteness of the physical strong coupling at low energies using hadronic $τ$ decays is shown.

hep-ex↗
arXiv2006

Tests of Quantum Chromo Dynamics at e^+e^- Colliders

The current status of tests of the theory of strong interactions, Quantum Chromo Dynamics (QCD), with data from hadron production in e^+e^- annihilation experiments is reviewed. The LEP experiments ALEPH, DELPHI, L3 and OPAL have published many analyses with data recorded on the Z^0 resonance at sqrt(s)=91.2 GeV and above up to sqrt(s)>200 GeV. There are also results from SLD at sqrt(s)=91.2 GeV and from reanalysis of data recorded by the JADE experiment at 14<sqrt(s)<44 GeV. The results of studies of jet and event shape observables, of particle production and of quark gluon jet differences are compared with predictions by perturbative QCD calculations. Determinations of the strong coupling constant alpha_S(M_Z) from jet and event shape observables, scaling violation and fragmentation functions, inclusive observables from Z^0 decays, hadronic tau decays and hadron production in low energy e^+e^- annihilation are discussed. Updates of the measurements are performed where new data or improved calculations have become available. Finally, investigations of the gauge structure of QCD are summarised.

hep-ex↗
arXiv2004

Studies of the 4-jet rate and of moments of event shape observables using JADE data

Data from e+e- annihilation into hadrons collected by the JADE experiment at centre-of-mass energies between 14 and 44 GeV were used to study the 4-jet rate using the Durham algorithm as well as the first five moments of event shape observables. The data were compared with NLO QCD predictions, augmented by resummed NLLA calculations for the 4-jet rate, in order to extract values of the strong coupling constant alpha_S. The preliminary results are alpha_S(MZ) = 0.1169 +/- 0.0026 (4-jet rate) and alpha_S(MZ) = 0.1286 +/- 0.0072 (moments) consistent with the world average value. For some of the higher moments systematic deficiencies of the QCD predictions are observed.

hep-ex↗
arXiv2002

Fragmentation functions using e+e- data from PETRA and LEP

We investigate fragmentation of charged particles in e+e- annihilation at 22, 35 and 44 GeV in terms of their polar angle and momentum distributions. From the angular distribution the ratio of longitudinal to total hadronic cross-section was determined at an average energy scale of 36.6 GeV to be $σ_L / σ_{tot} = 0.076 \pm 0.013$. At next-to-leading order this yields $ α_S (36.6 GeV) = 0.150 \pm 0.025 $. The $ξ= \ln (1/x)$ distributions were used in conjunction with OPAL data from 91-208 GeV to study the scale dependence of the maximum position, $ξ_0$. We studied flavour dependence of $ξ_0$ as a possible explanation of this problem, using direct flavour dependent measurements of $ξ_0$ at 91 GeV by OPAL.

hep-ex↗
arXiv2000

Power correction analyses in e+e- annihilation

The current status of theoretical work and experimental analyses on power corrections in QCD for e+e- annihilation will be reviewed. Measurements of the number of active quark flavours n_f and the QCD colour factors C_A and C_F derived from QCD fits to event shape distributions at lower energies and LEP energies will be presented. The fits are based on O(alpha_s^2)+NLLA QCD predictions with power corrections to model hadronisation.

hep-ex↗