27 research outputs found

    Seeing The Light (higgs): Searches And Measurements Of Higgs Boson Decays To Photons

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    This dissertation presents two results involving Standard Model Higgs bosons decaying to at least one photon. These analyses are performed using 79.8/fb of proton-proton collisions collected at √s=13 TeV with the ATLAS detector at the Large Hadron Collider. Differential and fiducial cross section measurements of the Higgs boson decaying to two photons are presented.The inclusive diphoton cross section was measured to be 55 ± 9 (stat.) ± 4 (syst.) ± 0.1 (theo.) fb compared with the Standard model prediction of 64 ± 2 fb. In addition to inclusive cross section measurement, fiducial cross section results are shown for regions targeting the vector boson fusion, VH, and ttH production modes of the Higgs boson as well as a region targeting beyond the Standard Model contributions. Differential results are given for multiple measured spectra involving kinematics of the diphoton system or variables with jets produced in association with the Higgs boson. No significant deviations from the Standard Model are observed and in their absence, limits are set on alternative hypotheses involving higher order couplings between Standard Model particles and the Higgs boson. Additionally, a search for a Standard Model Higgs bosons decaying into at least one photon and missing transverse momentum was performed.The photon can arise from a Higgs boson decaying into one or two neutralinos, which in turn decay into a gravitino and photon.Higgs bosons produced in association with a Z boson are considered in order to reduce the number of background events. No excess with respect to the Standard Model prediction is observed. Assuming a Standard Model ZH production cross section, the branching fraction of a Higgs boson to neutralinos or neutralino/gravitino is constrained to be less than 5-11% at the 95% confidence level for nearly massless gravitinos

    Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

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    A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

    Search for single production of vector-like quarks decaying into Wb in pp collisions at s=8\sqrt{s} = 8 TeV with the ATLAS detector

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    Measurements of top-quark pair differential cross-sections in the eμe\mu channel in pppp collisions at s=13\sqrt{s} = 13 TeV using the ATLAS detector

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    Measurement of the charge asymmetry in top-quark pair production in the lepton-plus-jets final state in pp collision data at s=8TeV\sqrt{s}=8\,\mathrm TeV{} with the ATLAS detector

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    Charged-particle distributions at low transverse momentum in s=13\sqrt{s} = 13 TeV pppp interactions measured with the ATLAS detector at the LHC

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    Measurement of the bbb\overline{b} dijet cross section in pp collisions at s=7\sqrt{s} = 7 TeV with the ATLAS detector

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    Measurement of jet fragmentation in Pb+Pb and pppp collisions at sNN=2.76\sqrt{{s_\mathrm{NN}}} = 2.76 TeV with the ATLAS detector at the LHC

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