3,467 research outputs found

    Does the `Higgs' have Spin Zero?

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    The Higgs boson is predicted to have spin zero. The ATLAS and CMS experiments have recently reported of an excess of events with mass ~ 125 GeV that has some of the characteristics expected for a Higgs boson. We address the questions whether there is already any evidence that this excess has spin zero, and how this possibility could be confirmed in the near future. The excess observed in the gamma gamma final state could not have spin one, leaving zero and two as open possibilities. We calculate the angular distribution of gamma gamma pairs from the decays of a spin-two boson produced in gluon-gluon collisions, showing that is unique and distinct from the spin-zero case. We also calculate the distributions for lepton pairs that would be produced in the W W* decays of a spin-two boson, which are very different from those in Higgs decays, and note that the kinematics of the event selection used to produce the excess observed in the W W* final state have reduced efficiency for spin two.Comment: 22 pages, 22 figures, Version accepted for publication in JHEP, includes additional plots of dilepton mass distribution

    Recent studies of top quark properties and decays at hadron colliders

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    The top quark is the heaviest known elementary particle. Observed for the first time in 1995 at the Tevatron by the CDF and D0 experiments, it has become object of several studies aimed at fully characterize its properties and decays. Precise determinations of top quark characteristics verify the internal consistency of the standard model and are sensitive to new physics phenomena. With the advent of the large top quark production rates generated at the LHC, top quark studies have reached unprecedented statistical precision. This review summarizes the recent measurements of top quark properties and studies of its decays performed at the LHC and Tevatron.Comment: 13 pages, 4 figures, 5 tables, Presented at Flavor Physics and CP Violation (FPCP 2012), Hefei, China, May 21-25, 201

    Cross Section Ratios between different CM energies at the LHC: opportunities for precision measurements and BSM sensitivity

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    The staged increase of the LHC beam energy provides a new class of interesting observables, namely ratios and double ratios of cross sections of various hard processes. The large degree of correlation of theoretical systematics in the cross section calculations at different energies leads to highly precise predictions for such ratios. We present in this letter few examples of such ratios, and discuss their possible implications, both in terms of opportunities for precision measurements and in terms of sensitivity to Beyond the Standard Model dynamics.Comment: 19 pages, 9 figure

    Where is SUSY?

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    The direct searches for Superymmetry at colliders can be complemented by direct searches for dark matter (DM) in underground experiments, if one assumes the Lightest Supersymmetric Particle (LSP) provides the dark matter of the universe. It will be shown that within the Constrained minimal Supersymmetric Model (CMSSM) the direct searches for DM are complementary to direct LHC searches for SUSY and Higgs particles using analytical formulae. A combined excluded region from LHC, WMAP and XENON100 will be provided, showing that within the CMSSM gluinos below 1 TeV and LSP masses below 160 GeV are excluded (m_{1/2} > 400 GeV) independent of the squark masses.Comment: 16 pages, 10 figure

    Top Quark Physics at the LHC: A Review of the First Two Years

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    This review summarizes the highlights in the area of top quark physics obtained with the two general purpose detectors ATLAS and CMS during the first two years of operation of the Large Hadron Collider LHC. It covers the 2010 and 2011 data taking periods, where the LHC provided pp collisions at a center-of-mass energy of sqrt(s)=7 TeV. Measurements are presented of the total and differential top quark pair production cross section in many different channels, the top quark mass and various other properties of the top quark and its interactions, for instance the charge asymmetry. Measurements of single top quark production and various searches for new physics involving top quarks are also discussed. The already very precise experimental data are in good agreement with the standard model.Comment: 107 pages, invited review for Int. J. Mod. Phys. A, v2 is identical to v1 except for the addition of the table of content

    Study of LHC Searches for a Lepton and Many Jets

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    Searches for new physics in high-multiplicity events with little or no missing energy are an important component of the LHC program, complementary to analyses that rely on missing energy. We consider the potential reach of searches for events with a lepton and six or more jets, and show they can provide increased sensitivity to many supersymmetric and exotic models that would not be detected through standard missing-energy analyses. Among these are supersymmetric models with gauge mediation, R-parity violation, and light hidden sectors. Moreover, ATLAS and CMS measurements suggest the primary background in this channel is from t-tbar, rather than W+jets or QCD, which reduces the complexity of background modeling necessary for such a search. We also comment on related searches where the lepton is replaced with another visible object, such as a Z boson.Comment: 23 pages, 12 figures, 1 tabl

    Bound-state/elementary-particle duality in the Higgs sector and the case for an excited 'Higgs' within the standard model

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    Though being weakly interacting, QED can support bound states. In principle, this can be expected for the weak interactions in the Higgs sector as well. In fact, it has been argued long ago that there should be a duality between bound states and the elementary particles in this sector, at least in leading order in an expansion in the Higgs condensate. Whether this remains true beyond the leading order is investigated using lattice simulations, and support is found. This provides a natural interpretation of peaks in cross sections as bound states. Unambiguously, this would imply the existence of (possibly very broad) resonances of Higgs and W and Z bound states within the standard model.Comment: 15 pages, 3 figures v2: added appendix with technical details, some minor improvement
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