Abstract
Charged Higgs bosons heavier than the top quark and decaying via $H^{\pm} \rightarrow tb$ are searched for in proton--proton collisions measured with the ATLAS experiment at $\sqrt{s}=8$ TeV corresponding to an integrated luminosity of 20.3 fb$^{-1}$. The production of a charged Higgs boson in association with a top quark, $gb \rightarrow tH^{\pm}$, is explored in the mass range 200 to 600 GeV using multi-jet final states with one electron or muon. In order to separate the signal from the Standard Model background, analysis techniques combining several kinematic variables are employed. An excess of events above the background-only hypothesis is observed across a wide mass range, amounting to up to 2.4 standard deviations. Upper limits are set on the $gb\rightarrow tH^{\pm}$ production cross section times the branching fraction $\mathrm{BR}(H^{\pm} \rightarrow tb)$. Additionally, the complementary $s$-channel production, $qq' \rightarrow H^{\pm}$, is investigated through a reinterpretation of $W' \rightarrow tb$ searches in ATLAS. Final states with one electron or muon are relevant for $H^{\pm}$ masses from 0.4 to 2.0 TeV, whereas the all-hadronic final state covers the range 1.5 to 3.0 TeV. In these search channels, no significant excesses from the predictions of the Standard Model are observed, and upper limits are placed on the $qq' \rightarrow H^{\pm}$ production cross section times the branching fraction BR$(H^{\pm} \rightarrow tb)$.
Highlights
Background and signal modellingThe background processes for the searches in this paper include SM pair production of top quarks, as well as the production of single-top-quark, W +jets, Z/γ∗+jets, diboson (W W/W Z/ZZ) and multi-jet events
This paper describes searches for charged Higgs bosons decaying into tb
The procedures for quantifying how well the data agree with the background-only hypothesis and for determining exclusion limits are based on the profile likelihood ratio test [107]
Summary
The first-level trigger (L1) is implemented in hardware, using a subset of detector information to reduce the event rate to no more than 75 kHz. The first-level trigger (L1) is implemented in hardware, using a subset of detector information to reduce the event rate to no more than 75 kHz This is followed by two software-based trigger levels (L2 and EF), which together further reduce the event rate to less than 400 Hz. Stringent data-quality requirements are applied, resulting in an integrated luminosity of 20.3 fb−1 for the 2012 data-taking period. The integrated luminosity has an uncertainty of 2.8%, measured following the methodology described in ref. Events are required to have a primary vertex with at least five associated tracks, each with a transverse momentum pT greater than 400 MeV. If an event has more than one reconstructed vertex satisfying these criteria, the primary vertex is defined as the reconstructed vertex with the largest sum of squared track transverse momenta
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