6,607 research outputs found

    LEP, SLC and the Standard Model

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    The period 1989-2000 provided a huge yield of precise electroweak data from the LEP and SLC experiments. Many analyses of these data are now complete, but others, particularly of the full LEP-2 data samples, continue. The main electroweak physics results from these data are summarised, and stringent tests of the Standard Model are made with the combined samples. The direct search for the missing link of the Standard Model, the Higgs boson, is also briefly reviewed.Comment: Invited talk at the XXXth SLAC Summer Institute Topical Conference, Stanford, California, USA, August 2002 (SSI02-TW05) 24 pages, LaTeX, 25 eps figure

    Precise Electroweak Results from LEP2

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    Precise electroweak results from LEP2 are reviewed.Comment: 16 pages, 10 figures, to appear in Proceedings of XIX International Symposium on Lepton and Photon Interactions at High Energies (LP'99

    Measurements of Rb_{b} using lifetime tags

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    Does haste make waste? The human factors of overtaking land design

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    The aim of this research was to improve overtaking safety and efficiency through improvements in road signage, markings, geometry and speed control associated with the placement and layout of passing lanes. The approach of the research was to explore the effects of several types of overtaking lane treatments in the safety and controlled environment of a state-of-the-art driving simulator. It was found that under the most benign conditions there were no differential effects of the three treatments. With poorer visibility or more taxing road geometry, the drivers relied more heavily on the road markings and signage and the effects of the treatments become more pronounced. The sensitivity to the more "challenging" situations was borne out by the greater speed differential between merge area sections at these sites

    Electroweak measurements using heavy quarks at LEP

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    Identification of diverse database subsets using property-based and fragment-based molecular descriptions

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    This paper reports a comparison of calculated molecular properties and of 2D fragment bit-strings when used for the selection of structurally diverse subsets of a file of 44295 compounds. MaxMin dissimilarity-based selection and k-means cluster-based selection are used to select subsets containing between 1% and 20% of the file. Investigation of the numbers of bioactive molecules in the selected subsets suggest: that the MaxMin subsets are noticeably superior to the k-means subsets; that the property-based descriptors are marginally superior to the fragment-based descriptors; and that both approaches are noticeably superior to random selection

    A trap-based pulsed positron beam optimised for positronium laser spectroscopy

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    We describe a pulsed positron beam that is optimised for positronium (Ps) laser-spectroscopy experiments. The system is based on a two-stage Surko-type buffer gas trap that produces 4 ns wide pulses containing up to 5 × 105 positrons at a rate of 0.5-10 Hz. By implanting positrons from the trap into a suitable target material, a dilute positronium gas with an initial density of the order of 107 cm−3 is created in vacuum. This is then probed with pulsed (ns) laser systems, where various Ps-laser interactions have been observed via changes in Ps annihilation rates using a fast gamma ray detector. We demonstrate the capabilities of the apparatus and detection methodology via the observation of Rydberg positronium atoms with principal quantum numbers ranging from 11 to 22 and the Stark broadening of the n = 2 → 11 transition in electric fields

    Antiproton-Hydrogen annihilation at sub-kelvin temperatures

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    The main properties of the interaction of ultra low-energy antiprotons (E≀10−6% E\le10^{-6} a.u.) with atomic hydrogen are established. They include the elastic and inelastic cross sections and Protonium (Pn) formation spectrum. The inverse Auger process (Pn+e→H+pˉPn+e \to H+\bar{p}) is taken into account in the framework of an unitary coupled-channels model. The annihilation cross-section is found to be several times smaller than the predictions made by the black sphere absorption models. A family of pˉH\bar{p}H nearthreshold metastable states is predicited. The dependence of Protonium formation probability on the position of such nearthreshold S-matrix singularities is analysed. An estimation for the HHˉH\bar{H} annihilation cross section is obtained.Comment: latex.tar.gz file, 22 pages, 9 figure