4,914 research outputs found

    Jet Physics at LEP and World Summary of αs\alpha_s

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    Recent results on jet physics and tests of QCD from hadronic final states in e+e−e^+e^- annihilation at PETRA and at LEP are reviewed, with special emphasis on hadronic event shapes, charged particle production rates, properties of quark and gluon jets and determinations of αs\alpha_s. The data in the entire energy range from PETRA to LEP-2 are in broad agreement with the QCD predictions. The world summary of measurements of αs\alpha_s is updated and a detailed discussion of various methods to determine the overall error of αs(MZ)\alpha_s (M_Z) is presented. The new world average is αs(MZ)=0.119±0.004\alpha_s (M_Z) = 0.119 \pm 0.004. The size of the error depends on the treatment of correlated uncertainties.Comment: Talk presented at the IVthIV^{th} Int. Symp. on Radiative Corrections, Barcelona, Sept. 8-12, 1998. 18 pages, 13 eps-figures; uses sprocl.sty and psfig.st

    Chirality of tensor perturbations for complex values of the Immirzi parameter

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    In this paper we generalise previous work on tensor perturbations in a de Sitter background in terms of Ashtekar variables to cover all complex values of the Immirzi parameter gamma (previous work was restricted to imaginary gamma). Particular attention is paid to the case of real gamma. Following the same approach as in the imaginary case, we can obtain physical graviton states by invoking reality and torsion free conditions. The Hamiltonian in terms of graviton states has the same form whether gamma has a real part or not; however changes occur for the vacuum energy and fluctuations. Specifically, we observe a gamma dependent chiral asymmetry in the vacuum fluctuations only if gamma has an imaginary part. Ordering prescriptions also change this asymmetry. We thus present a measurable result for CMB polarisation experiments that could shed light on the workings of quantum gravity.Comment: 6 pages, 1 figur

    Techniques for QCD calculations by numerical integration

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    Calculations of observables in quantum chromodynamics are typically performed using a method that combines numerical integrations over the momenta of final state particles with analytical integrations over the momenta of virtual particles. I describe the most important steps of a method for performing all of the integrations numerically.Comment: 36 pages with 16 postscript figure

    QCD in e+e- collisions at 2 TeV

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    We discuss some topics in QCD studies at 2 TeV. Particular emphasis is given to the separation of pure QCD events from the WW and the t-tbar backgroundsComment: 10 pages, Latex, epsfig, 7 figures To appear in the Proceedings of the 1995 "Workshop on Physics with e+e- Linear Colliders", Annecy-Gran Sasso-DES

    Quark-Gluon Jet Differences at LEP

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    A new method to identify the gluon jet in 3-jet ``{\bf Y}'' decays of Z0Z^0 is presented. The method is based on differences in particle multiplicity between quark jets and gluon jets, and is more effective than tagging by leptonic decay. An experimental test of the method and its application to a study of the ``string effect'' are proposed. Various jet-finding schemes for 3-jet events are compared.Comment: 11 pages, LaTeX, 4 PostScript figures availble from the author ([email protected]), MSUTH-92-0

    Tests of Power Corrections for Event Shapes in e+e- Annihilation

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    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 Power Corrections to Event Shape Distributions from e+e- Annihilation

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    A study of differential event shape distributions using e+e- data at centre-of-mass energies of 35 to 183 GeV is presented. We investigated non-perturbative power corrections for the thrust, C-parameter, total and wide jet broadening observables. We observe a good description of the distributions by the combined resummed QCD calculations plus power corrections from the dispersive approach. The single non-perturbative parameter \alpha_0 is measured to be \alpha_0 (2 GeV) = 0.502 +- 0.013 (stat.) ^{+0.046)_{-0.032} (exp. syst.) ^{+0.074}_{-0.053} (theo. syst.) and is found to be universal for the observables studied within the given systematic uncertainties. Using revised calculations of the power corrections for the jet broadening variables, improved consistency of the individual fit results is obtained. Agreement is also found with results extracted from the mean values of event shape distributions.Comment: 19 pages, LaTeX2e, 8 .eps-files included, paper contributed to the EPS-HEP99 conference in Tampere, Finlan

    Interteaching: Types of prep guide questions and their effect on student quiz performance

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    Although previous research indicates that interteaching is an effective alternative to more traditional teaching approaches, not many component analyses of the method exist. For example, although researchers have shown that the prep guide component contributes to the effectiveness of interteaching, no research has directly examined how the content of the prep guides affects learning. The current lab-based study investigated whether having prep guides consisting of lower-level or higher-level questions impacted students’ subsequent quiz performance. We found no significant differences in quiz performance between the two conditions, but several extraneous factors may have impacted the results

    Cultural Bias in the Perception of Foreign-Policy Events

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    Cultural bias means individuals judge and interpret a phenomenon according to values that are inherent in their own culture. The same event may be perceived differently by individuals with different cultural backgrounds. This study systematically tests for the presence of cultural differences in the perception of foreign policy events. Using a web survey with a split-sample of Chinese and US foreign policy experts, four domains of foreign policy are explored: sanctions; border violations; foreign aid; and trade agreements. The findings indicate general agreement between Chinese and US experts in the classification of foreign-policy events as cooperative, neutral, or conflictive. In regard to more specific foreign-policy scenarios, the picture is more differentiated. In the case of economic sanctions and border violations, there appears, again, to be general agreement as to the degree of conflictiveness of these events. In addition, perception does not appear to be influenced by collective self-esteem, in the sense that responses remain similar whether the event is described in abstract or country-specific terms. In the case of trade agreements and foreign aid, by contrast, there is a divergence in Chinese and US perceptions in regard to contextual factors such as conditionality and enforcement. Overall, the study suggests that while culture rarely affects the general perception of foreign-policy events, it does play a role in the perception of more complex concepts, such as conditionality and enforcement, that structure the context and meaning of those events