Higgs production in association with top quarks at the LHC

[摘要] Since it has been found that the MadGraph Monte Carlo generator offers superiorflavour-matching capability as compared to Alpgen, the suitability of MadGraphfor the generation of ttb¯ ¯b events is explored, with a view to simulating this backgroundin searches for the Standard Model Higgs production and decay processttH, H ¯ → b¯b. Comparisons are performed between the output of MadGraph andthat of Alpgen, showing that satisfactory agreement in their predictions can beobtained with the appropriate generator settings.A search for the Standard Model Higgs boson, produced in association with the topquark and decaying into a b¯b pair, using 20.3 fb−1of 8 TeV collision data collectedin 2012 by the ATLAS experiment at CERN’s Large Hadron Collider, is presented.The GlaNtp analysis framework, together with the RooFit package and associatedsoftware, are used to obtain an expected 95% confidence-level limit of 4.2+4.1−2.0timesthe Standard Model expectation, and the corresponding observed limit is found tobe 5.9; this is within experimental uncertainty of the published result of the analysisperformed by the ATLAS collaboration.A search for a heavy charged Higgs boson of mass mH± in the range200 ≤ mH± /GeV ≤ 600, where the Higgs mediates the five-flavour beyond-theStandard-Modelphysics process gb → tH± → ttb, with one top quark decaying leptonicallyand the other decaying hadronically, is presented, using the 20.3 fb−18 TeVATLAS data set. Upper limits on the product of the production cross-section andthe branching ratio of the H± boson are computed for six mass points, and theseare found to be compatible within experimental uncertainty with those obtained bythe corresponding published ATLAS analysis.

[发布机构] University:University of Glasgow;Department:School of Physics and Astronomy

[关键词] science, experimental, particle, physics, data, analysis, Higgs, ATLAS, CERN, standard, model, supersymmetry, top, quark, BSM, MSSM, ttH, SUSY.