3,607 research outputs found

    Overview of physics at the Large Hadron Collider

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    The Large Hadron Collider has produced during the run from 2010 to 2012, proton-proton collision to a center-of-mass energy up to 8TeV. The data delivered to the experiments placed along the ring allowed studies of the hadron collision physics at this unprecedent energy scale, and accurate checks of the Standard Model have been performed. An overview of the most representative physics results achieved are briefly presented and discussed, with emphasis to the most recent studies made. In particular, an update on the first measurements of the new resonance with mass around 125 GeV is reported

    Phenomenology of the minimal supersymmetric U(1)BL×U(1)RU(1)_{B-L}\times U(1)_R extension of the standard model

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    We discuss the minimal supersymmetric U(1)BL×U(1)RU(1)_{B-L}\times U(1)_R extension of the standard model. Gauge couplings unify as in the MSSM, even if the scale of U(1)BL×U(1)RU(1)_{B-L}\times U(1)_R breaking is as low as order TeV and the model can be embedded into an SO(10) grand unified theory. The phenomenology of the model differs in some important aspects from the MSSM, leading potentially to rich phenomenology at the LHC. It predicts more light Higgs states and the mostly left CP-even Higgs has a mass reaching easily 125 GeV, with no constraints on the SUSY spectrum. Right sneutrinos can be the lightest supersymmetric particle, changing all dark matter constraints on SUSY parameter space. The model has seven neutralinos and squark/gluino decay chains involve more complicated cascades than in the MSSM. We also discuss briefly low-energy and accelerator constraints on the model, where the most important limits come from recent ZZ' searches at the LHC and upper limits on lepton flavour violation.Comment: 46 pages, 11 figure

    Structure of dimension-six derivative interactions in pseudo Nambu-Goldstone N Higgs doublet models

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    We derive the general structure of dimension-six derivative interactions in the N Higgs doublet models, where Higgs fields arise as pseudo Nambu-Goldstone modes of a strongly interacting sector. We show that there are several relations among the dimension-six operators, and therefore the number of independent operators decreases compared with models on which only SU(2)_L x U(1)_Y invariance is imposed. As an explicit example, we derive scattering amplitudes of longitudinal gauge bosons and Higgs bosons at high energy on models involving two Higgs doublets, and compare them with the amplitudes in the case of one Higgs doublet.Comment: 49 pages, 10 figure

    Standard Model Higgs boson searches with the ATLAS detector at the Large Hadron Collider

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    The investigation of the mechanism responsible for electroweak symmetry breaking is one of the most important tasks of the scientific program of the Large Hadron Collider. The experimental results on the search of the Standard Model Higgs boson with 1 to 2 fb^-1 of proton proton collision data at sqrt s=7 TeV recorded by the ATLAS detector are presented and discussed. No significant excess of events is found with respect to the expectations from Standard Model processes, and the production of a Higgs boson is excluded at 95% Confidence Level for the mass regions 144-232, 256-282 and 296-466 GeV.Comment: Proceedings of the Lepton Photon 2011 Conference, to appear in "Pramana - journal of phsyics". 11 pages, 13 figure

    Implications of a high mass light MSSM Higgs scalar for SUSY searches at the LHC

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    The Atlas and CMS collaborations have both reported an excess of events in the WW\star \rightarrow \ell+\ell- + ETmiss search channel, which could be the first evidence for the Higgs boson. In the context of the MSSM, the lightest SUSY Higgs scalar h is expected to occur with mass mh = 135 GeV, depending on the range of SUSY parameters scanned over. Since the h \rightarrow WW\star branching fraction falls swiftly with decreasing mh, a signal in the WW\star channel would favor an h at the high end of its predicted mass range. We scan over general GUT scale SUSY model parameters to find those which give rise to mh > 130 GeV. A value of m0 \sim 10 - 20 TeV is favored, with A0 \sim \pm2m0, while the lower range of m1/2 < 1 TeV is also slightly favored. This gives rise to an "effective SUSY" type of sparticle mass spectrum. For low m1/2, gluino pair production followed by three-body gluino decay to top quarks may ultimately be accesible to LHC searches, while for higher m1/2 values, the SUSY spectra would likely be out of range of any conceivable LHC reach. Since the thermal neutralino relic abundance tends to be very high, late-time entropy dilution or neutralino decay to light axinos would be required to gain accord with the measured dark matter abundanceComment: 12 pages, 3 figures, some references added, accepted in PR

    Measurement of the Superparticle Mass Spectrum in the Long-Lived Stau Scenario at the LHC

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    In supersymmetric scenarios with a long-lived stau, the LHC experiments provide us with a great environment for precise mass measurements of superparticles. We study a case in which the mass differences between the lightest stau and other sleptons are about 10 GeV or larger, so that the decay products of heavier sleptons are hard enough to be detected. We demonstrate that the masses of neutralinos, sleptons, and squarks can be measured with a good accuracy.Comment: 20 pages, 6 figure

    Interactions of Heavy Hadrons using Regge Phenomenology and the Quark Gluon String Model

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    The search for stable heavy exotic hadrons is a promising way to observe new physics processes at collider experiments. The discovery potential for such particles can be enhanced or suppressed by their interactions with detector material. This paper describes a model for the interactions in matter of stable hadrons containing an exotic quark of charges ±1/3e\pm {1/3}e or ±2/3e\pm {2/3}e using Regge phenomenology and the Quark Gluon String Model. The influence of such interactions on searches at the LHC is also discussed

    Calculation of the One W Loop HγγH \to \gamma \gamma Decay Amplitude with a Lattice Regulator

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    There has been a controversial recent claim that the standard result on the Higgs to two photon decay rate is incorrect, with the use of dimensional regularization fingered as the alleged culprit. Given the great importance of the HγγH\to \gamma \gamma process as a possible Standard Model Higgs discovery channel at the LHC if the Higgs mass is light, it is critical to find a way to check the correctness of the results of dimensional regularization for this process. Here we report the results of a perturbative calculation of the HγγH\to \gamma \gamma decay amplitude using a spacetime lattice as a UV regulator, which is the only known gauge-invariant regulator for non-Abelian gauge theories other than dimensional regularization. We find that the decay amplitude calculated using lattice-regularized perturbation theory is consistent to very high statistical accuracy with the decay amplitude obtained using dimensional regularization.Comment: 5 pages, 4 figure
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