1,737 research outputs found

    A Fresh Look at Gauge Coupling Unification

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    The apparent unification of gauge couplings around 10^16 GeV is one of the strong arguments in favor of Supersymmetric extensions of the Standard Model (SM). In this contribution a new analysis, using the latest experimental data, is performed. The strong coupling alpha_s emerges as the key factor for evaluating the results of the fits, as the experimental and theoretical uncertainties in its measurements are substantially higher than for the electromagnetic and weak couplings. The present analysis pays special attention to numerical and statistical details. The results, combined with the current limits on the supersymmetric particle masses, favor a value for the SUSY scale <~ 150 GeV and for alpha_s = 0.118-0.119.Comment: 4 pages, 1 table, 1 figure; presented at the Meeting of the Division of Particles and Fields of the APS, Riverside, USA, August 200

    Sensitivity to Contact Interactions and Extra Dimensions in Di-lepton and Di-photon Channels at Future Colliders

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    Virtual effects from a generic description of physics beyond the Standard Model in terms of contact interactions, or from large extra dimensions will modify the observed cross sections for easy to detect final states like lepton or photon pairs, and can be used to probe scales much higher than the center-of-mass energy of the partons initiating the interactions. In this note the sensitivity reach of the Large Hadron Collider to contact interactions in the Drell-Yan channels and of a Future Linear Collider to contact interactions and extra dimensions in e+e−e^+e^-, ÎŒ+Ό−\mu^+\mu^- and γγ\gamma\gamma final states are studied. Experimental aspects of the measurements, systematic error effects and the evolution of the search reach with accumulated luminosity are considered.Comment: 13 pages, 2 figures, 8 tables; Contribution to LHC / LC Study Group Working Documen

    Other BSM Searches at the LHC

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    A review of the discovery potential of LHC for new phenomena beyond the Standard Model (BSM) other than Supersymmetry in the early phase of running is presented. Topics covered include searches for extra dimensions in different scenarios (ADD, Randall-Sundrum, black holes ...), resonance hunting in di-lepton, di-photon and di-jet final states, searches for contact interactions, heavy stable charged particles, technicolor, etc. The strategies of the ATLAS and CMS experiments to understand the detectors and prepare them for "search" mode and the prospects for discoveries using early data are described.Comment: 9 pages, 11 figures, Invited LHC review talk at HCP2008, 19th Hadron Collider Physics Symposium 2008, Galena, IL, USA, May 27-31 200

    Strong Coupling Running, Gauge Coupling Unification and the Scale of New Physics

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    The apparent unification of gauge couplings in Grand Unified Theories around 1016^{16} GeV is one of the strong arguments in favor of Supersymmetric extensions of the Standard Model. In this paper, an analysis of the measurements of the strong coupling running from the CMS experiment at the LHC is combined with a "traditional" gauge coupling unification analysis using data at the Z peak. This approach places powerful constraints on the possible scales of new physics and on the parameters around the unification scale. A supersymmetric analysis without GUT threshold corrections describes the CMS data well and provides perfect unification. The favored scales are $M_{SUSY}\ =\ 2820\ +670\ -540GeVand GeV and M_{GUT}\ =\ 1.05 \pm 0.06 \cdot 10^{16}$ GeV. For zero or small threshold corrections the scale of new physics may be well within LHC reach.Comment: 11 pages, 4 figures, 2 table

    Study of Parton Density Function Uncertainties with LHAPDF and PYTHIA at LHC

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    The experimental errors in current and future hadron colliders are expected to decrease to a level that will challenge the uncertainties in the theoretical calculations. One important component in the prediction uncertainties comes from the Parton Density Functions of the (anti)proton. In this work we develop an interface from the Les Houches Accord Parton Density Functions (LHAPDF) package to the very popular Monte Carlo generator {\tt PYTHIA} version 6.2. Then we proceed to estimate the PDF uncertainties for the production of Drell-Yan pairs from the Z pole to masses above 1 \TeV and for Higgs bosons at LHC. The measurement of the electro-weak mixing angle at LHC as a particularly difficult case is studied.Comment: 8 pages, 5 tables; code available on request from the author; Contribution to LHC / LC Study Group Working Documen

    Gauge Coupling Unification, SUSY Scale and Strong Coupling Running

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    The apparent unification of gauge couplings around 10^16 GeV is one of the strong arguments in favor of Supersymmetric extensions of the Standard Model (SM). In this contribution two new analyses of the gauge coupling running, the latter using in contrast to previous studies not data at the Z peak but at LEP2 energies, are presented. The generic SUSY scale in the more precise novel approach is 93 < M_SUSY < 183 GeV, easily within LHC, and possibly even within Tevatron reach.Comment: 3 pages, 1 table, 2 figures; presented at PANIC05, Particles and Nuclei International Conference, Santa Fe, New Mexico, October 24-28, 200

    Fermion-pair Production above the Z and Search for New Phenomena

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    A review of the measurements of hadron, flavour-tagged and lepton-pair production cross-sections and lepton-pair forward-backward asymmetries performed by the four LEP experiments ALEPH, DELPHI, L3 and OPAL at energies between 130 and 183 GeV is given. All 183 GeV results are preliminary. The searches by the four collaborations for new physics phenomena like contact interactions and compositeness, exchange of R-parity violating sneutrinos or squarks, leptoquarks or additional heavy gauge bosons Z' are summarized. No evidence for deviations from the Standard Model expectations is found and new or improved limits are derived.Comment: 6 pages, 3 figures, 2 tables, presented at the XXXIInd Rencontres de Moriond, Electroweak Interactions and Unified Theories, Les Arcs, France, March 14-21, 199