1,936 research outputs found

    Recent Tests of QCD at SLD

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    We present selected results on strong interaction physics from the SLD experiment at the SLAC Linear Collider. We report on several new studies of 3- and 4-jet hadronic Z decays, in which jets are identified as quark, antiquark or gluon. The 3-jet Z^0->b\bar{b}g rate is sensitive to the b-quark mass; prospects for measuring m_b are discussed. The gluon energy spectrum is measured over the full kinematic range, providing an improved test of QCD and limits on anomalous bbg couplings. The parity violation in Z^0->b\bar{b}g decays is consistent with electroweak theory plus QCD. New tests of T- and CP-conservation at the bbg vertex are performed. A new measurement of the rate of gluon splitting into b\bar{b} pairs yields g_{b\bar{b}}=0.0031+-0.0007(stat.)+-0.0006(syst.) (Preliminary). We also present a number of new results on jet fragmentation into identified hadrons. The B hadron energy spectrum is measured over the full kinematic range using a new, inclusive technique, allowing stringent tests of predictions for its shape and a precise measurement of =0.714+-0.005(stat.)+-0.007(syst.) (Preliminary). A detailed study of correlations in rapidity y between pairs of identified pions, kaons and protons confirms that strangeness and baryon number are conserved locally, and shows local charge conservation between meson-baryon and strange-nonstrange pairs. Flavor-dependent long-range correlations are observed for all combinations of these hadron species, yielding new information on leading particle production. The first study of correlations using rapidities signed such that y>0 corresponds to the quark direction provides additional new insights into fragmentation, including the first direct observation of baryon number ordering along the q\bar{q} axis.Comment: 20 pages, 12 figs.; talk given at the QCD99 meeting, Montpellier, France, 7-13 July, 1999; a smaller-print version will appear in the proceeding

    Introduction to Collider Physics

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    This is a set of four lectures presented at the Theoretical Advanced Study Institute (TASI-09) in June 2009. The goal of the lectures is to introduce students to some of the basic ideas and tools required for theoretical analysis of collider data. Several examples of Standard Model processes at electron-positron and hadron colliders are considered to illustrate these ideas. In addition, a general strategy for formulating searches for physics beyond the Standard Model is outlined. The lectures conclude with a brief survey of recent, ongoing and future searches for the Higgs boson and supersymmetric particles.Comment: 47 pages, 34 figures, contributed to TASI-09 proceedings. One reference added in v

    Heavy Quarkonium Physics

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    This report is the result of the collaboration and research effort of the Quarkonium Working Group over the last three years. It provides a comprehensive overview of the state of the art in heavy-quarkonium theory and experiment, covering quarkonium spectroscopy, decay, and production, the determination of QCD parameters from quarkonium observables, quarkonia in media, and the effects on quarkonia of physics beyond the Standard Model. An introduction to common theoretical and experimental tools is included. Future opportunities for research in quarkonium physics are also discussed.Comment: xviii + 487 pages, 260 figures. The full text is also available at the Quarkonium Working Group web page: http://www.qwg.to.infn.i

    Review of Top Quark Physics

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    We present an overview of Top Quark Physics - from what has been learned so far at the Tevatron, to the searches that lie ahead at present and future colliders. We summarize the richness of the measurements and discuss their possible impact on our understanding of the Standard Model by pointing out their key elements and limitations. When possible, we discuss how the top quark may provide a connection to new or unexpected physics.Comment: 84 pp. With permission from the Annual Review of Nuclear & Particle Science. Final version of this material is scheduled to appear in the Annual Review of Nuclear & Particle Science Vol. 53, to be published in December 2003 by Annual Reviews (http://www.annualreviews.org

    The Physics of Hadronic Tau Decays

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    Hadronic tau decays represent a clean laboratory for the precise study of quantum chromodynamics (QCD). Observables (sum rules) based on the spectral functions of hadronic tau decays can be related to QCD quark-level calculations to determine fundamental quantities like the strong coupling constant, parameters of the chiral Lagrangian, |V_us|, the mass of the strange quark, and to simultaneously test the concept of quark-hadron duality. Using the best available measurements and a revisited analysis of the theoretical framework, the value alpha_s(m_tau) = 0.345 +- 0.004[exp] +- 0.009[theo] is obtained. Taken together with the determination of alpha_s(m_Z) from the global electroweak fit, this result leads to the most accurate test of asymptotic freedom: the value of the logarithmic slope of 1/alpha_s(s) is found to agree with QCD at a precision of 4%. In another approach, the tau spectral functions can be used to determine hadronic quantities that, due to the nonperturbative nature of long-distance QCD, cannot be computed from first principles. An example for this is the contribution from hadronic vacuum polarization to loop-dominated processes like the anomalous magnetic moment of the muon. This article reviews the measurements of nonstrange and strange tau spectral functions and their phenomenological applications.Comment: 89 pages, 32 figures; final version accepted for publication by Reviews of Modern Physic
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