4,443 research outputs found
Review of alpha_s Measurements
We present a review of measurements of alpha_S. The individual measurements
are discussed and intermediate averages for classes of related measurements are
found. The final average is built using the intermediate values. Correlations
are treated consistently. The ICHEP 2006 world average is alpha_S(M_Z) = 0.1175
+/- 0.0011 dominated by the recent result from lattice QCD.Comment: 4 pages, 1 figure, 1 table, contribution to ICHEP 2006 (Moscow)
proceeding
Extended x-ray absorption fine structure study of porous GaSb formed by ion implantation
Porous GaSb has been formed by Ga ion implantation into crystalline GaSb substrates at either room temperature or −180 °C. The morphology has been characterized using scanning electron microscopy and the atomic structure was determined using extended x-ray absorption fine structure spectroscopy. Room-temperature implantation at low fluences leads to the formation of ∼20-nm voids though the material remains crystalline. Higher fluences cause the microstructure to evolve into a network of amorphous GaSb rods ∼15 nm in diameter. In contrast, implantation at −180 °C generates large, elongated voids but no rods. Upon exposure to air, the surface of the porous material is readily oxidized yielding Ga₂O₃ and metallic Sb precipitates, the latter resulting from the reduction of unstable Sb₂O₃. We consider and discuss the atomic-scale mechanisms potentially operative during the concurrent crystalline-to-amorphous and continuous-to-porous transformations
Tests of Power Corrections for Event Shapes in e+e- Annihilation
A study of perturbative QCD calculations combined with power corrections to
model hadronisation effects is presented. The QCD predictions are fitted to
differential distributions and mean values of event shape observables measured
in e+e- annihilation at centre-of-mass energies from 14 to 189 GeV. We
investigate the event shape observables thrust, heavy jet mass, C-parameter,
total and wide jet broadening and differential 2-jet rate and observe a good
description of the data by the QCD predictions. The strong coupling constant
alpha_S(M_Z) and the free parameter of the power correction calculations
alpha_0(2 GeV) are measured to be alpha_S(M_Z) = 0.1171 +/- 0.0032/0.0020 and
alpha_0(2 GeV) = 0.513 +/- 0.066/0.045. The predicted universality of alpha_0
is confirmed within the uncertainties of the measurements.Comment: 28 pages, LaTeX2e, 21 .eps-files included, accepted by Eur. Phys. J.
Tests of hard and soft QCD with e+e- Annihilation Data
Experimental tests of QCD predictions for event shape distributions combining
contributions from hard and soft processes are discussed. The hard processes
are predicted by perturbative QCD calculations. The soft processes cannot be
calculated directly using perturbative QCD, they are treated by a power
correction model based on the analysis of infrared renormalons. Furthermore, an
analysis of the gauge structure of QCD is presented using fits of the colour
factors within the same combined QCD predictions.Comment: 6 pages, 7 figures, contribution to Siena 2001, Seventh Topical
Seminar on The legacy of LEP and SLC, Siena, Italy, 8 to 11 October 2001,
proceedings to appear in Nucl. Phys. B (Proc. Suppl.
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.Comment: Contribution to High Energy Physics International Conference on
Quantum Chromo Dynamics (QCD00), Montpellier, 6 to 12 July, 200
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