Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector

Abstract

A search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb${}^{-1}$ of proton-proton collision data recorded by the ATLAS experiment at $\sqrt{s}=8$ TeV at the Large Hadron Collider. Five final states, targeting the decays $H\to W{W}^{\ast }$, $\tau \tau$, and $Z{Z}^{\ast }$, are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons ($e$ or $\mu$) without a hadronically decaying $\tau$ lepton; three light leptons; two same-charge light leptons with a hadronically decaying $\tau$ lepton; four light leptons; and one light lepton and two hadronically decaying $\tau$ leptons. No significant excess of events is observed above the background expectation. The best fit for the $t\bar{t}H$ production cross section, assuming a Higgs boson mass of 125 GeV, is $2.1_{-1.2}^{+1.4}$ times the SM expectation, and the observed (expected) upper limit at the 95% confidence level is 4.7 (2.4) times the SM rate. The $p$-value for compatibility with the background-only hypothesis is $1.8\sigma$; the expectation in the presence of a Standard Model signal is $0.9\sigma$.

14 pages plus author list + cover pages (26 pages total), 3 figures, 5 tables, submitted to Phys. Lett. B, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2013-26/

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