Search for Higgs Boson Pair Production in the $\gamma \gamma b\overline{b}$ Final State Using $pp$ Collision Data at $\sqrt{s}=8\mathrm{TeV}$ from the ATLAS Detector

Searches are performed for resonant and nonresonant Higgs boson pair production in the $\gamma \gamma b\overline{b}$ final state using $20{\mathrm{fb}}^{-1}$ of proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the CERN Large Hadron Collider. A 95% confidence level upper limit on the cross section times branching ratio of nonresonant production is set at 2.2 pb, while the expected limit is 1.0 pb. The difference derives from a modest excess of events, corresponding to 2.4 standard deviations from the background-only hypothesis. The limit observed in the search for a narrow $X\to hh$ resonance ranges between 0.7 and 3.5 pb as a function of the resonance mass.

Figure 1

Upper plot: diphoton invariant mass spectrum for data and the corresponding fitted signal and background in the signal region for the nonresonance search. Lower plot: the diphoton invariant mass spectrum in the continuum background from events with fewer than two $b$ tags and the corresponding fitted curve, the shape of which is also used in the upper plot.

Figure 2

Upper plot: the constrained four-object invariant mass $m_{\gamma \gamma jj}$ for data events in the resonance signal region. The expected backgrounds are also shown. A narrow width resonance at 300 GeV is displayed for comparison only. Lower plot: the diphoton invariant mass spectrum in the continuum background from events with fewer than two $b$ tags and the corresponding fitted curve, the shape of which is also used in the upper plot.

Figure 3

A 95% CL upper limit on the cross section times branching ratio of a narrow resonance decaying to pairs of Higgs bosons as a function of $m_X$ (see text for more details).