Search for charged Higgs bosons in the $H^{\pm} \rightarrow tb$ decay channel in $pp$ collisions at $\sqrt{s} = 8$ TeV using the ATLAS detector

TL;DR

This paper reports a search for heavy charged Higgs bosons decaying into top and bottom quarks in proton-proton collisions at 8 TeV using the ATLAS detector, employing advanced analysis techniques to set limits on production cross sections.

Contribution

It introduces a comprehensive search strategy for charged Higgs bosons in multiple production channels and final states, extending previous searches with new analysis methods and reinterpretations.

Findings

Observed a 2.4 sigma excess in some mass ranges.

Set upper limits on $gb ightarrow tH^{ ext{±}}$ production cross section.

Set upper limits on $qq' ightarrow H^{ ext{±}}$ production cross section.

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$(H^{\pm} \rightarrow tb)$.