Abstract
Searches are performed for resonant and nonresonant Higgs boson pair production in the γγbb[over ¯] final state using 20 fb^{-1} of proton-proton collisions at a center-of-mass energy of 8TeV 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 2.2pb, while the expected limit is 1.0pb. 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→hh resonance ranges between 0.7 and 3.5pb as a function of the resonance mass.
Highlights
Background events with a singleHiggs boson produced in association with a W or Z boson or tt (Wh, Zh, tth) are simulated with PYTHIA8 [24] using CTEQ6L1 parton distribution functions of the proton (PDFs) [25]
Searches are performed for resonant and nonresonant Higgs boson pair production in the γγbbfinal state using 20 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
Background events with a single Higgs boson produced in association with a W or Z boson or tt (Wh, Zh, tth) are simulated with PYTHIA8 [24] using CTEQ6L1 parton distribution functions of the proton (PDFs) [25]
Summary
Searches are performed for resonant and nonresonant Higgs boson pair production in the γγbbfinal state using 20 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. The background and potential signal are fit to the unbinned mγγ distribution of all events passing the dijet and diphoton selections described above This fit has three components: the signal with a pair of Higgs bosons, the background processes with a single Higgs boson resonant at mγγ 1⁄4 mh, and the continuum background. The mγγ resolution is set to the expected value of 1.6 GeV The acceptance of this requirement on background events without Higgs bosons, εmγγ , is measured by fitting an exponential function to the mγγ sidebands for events with fewer than two b-tagged jets. For this fit, the mγγ region of mh Æ 5 GeV is excluded to eliminate any potential contamination from resonant Higgs boson production. The combined acceptance and selection efficiency for a resonance signal to pass
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