This Letter reports evidence of triple gauge boson production pp arrow right W((scriptlv) gamma gamma +X, which is accessible for the first time with the 8 TeV LHC data set. The fiducial cross ...section for this process is measured in a data sample corresponding to an integrated luminosity of 20.3 fb-1, collected by the ATLAS detector in 2012. Events are selected using the W boson decay to ev or mu v as well as requiring two isolated photons. The measured cross section is used to set limits on anomalous quartic gauge couplings in the high diphoton mass region.
This Letter presents a search for a heavy neutral particle decaying into an opposite-sign different-flavor dilepton pair, e±μ∓, e±τ∓, or μ±τ∓ using 20.3 fb-1 of pp collision data at √s=8 TeV ...collected by the ATLAS detector at the LHC. The numbers of observed candidate events are compatible with the standard model expectations. In addition, limits are set on the cross section of new phenomena in two scenarios: the production of ν˜τ in R-parity-violating supersymmetric models and the production of a lepton-flavor-violating Z' vector boson.
A search for a charged Higgs boson, H+ or -, decaying to a W+ or - boson and a Z boson is presented. The search is based on 20.3 fb-1 of proton-proton collision data at a center-of-mass energy of 8 ...TeV recorded with the ATLAS detector at the LHC. The H+ or - boson is assumed to be produced via vector-boson fusion and the decays W+ or - arrow right qq' super(-) and Z arrow right e+e-/ mu + mu - are considered. The search is performed in a range of charged Higgs boson masses from 200 to 1000 GeV. No evidence for the production of an H+ or - boson is observed. Upper limits of 31-1020 fb at 95% C.L. are placed on the cross section for vector-boson fusion production of an H+ or - boson times its branching fraction to W+ or -Z. The limits are compared with predictions from the Georgi-Machacek Higgs triplet model.
A search for a charged Higgs boson, H±, decaying to a W± boson and a Z boson is presented. The search is based on 20.3 fb–1 of proton-proton collision data at a center-of-mass energy of 8 TeV ...recorded with the ATLAS detector at the LHC. The H± boson is assumed to be produced via vector-boson fusion and the decays W± → qq¯' and Z → e+e–/μ+μ– are considered. The search is performed in a range of charged Higgs boson masses from 200 to 1000 GeV. No evidence for the production of an H± boson is observed. Upper limits of 31–1020 fb at 95% C.L. are placed on the cross section for vector-boson fusion production of an H± boson times its branching fraction to W±Z. The limits are compared with predictions from the Georgi-Machacek Higgs triplet model.
A search for new particles that decay into top quark pairs is reported. The search is performed with the ATLAS experiment at the LHC using an integrated luminosity of 20.3 fb-1 of proton-proton ...collision data collected at a centre-of-mass energy of \( \sqrt{s}=8 \) TeV. The lepton-plus-jets final state is used, where the top pair decays to \( {W}^{+}b{W}^{-}\overline{b} \), with one W boson decaying leptonically and the other hadronically. The invariant mass spectrum of top quark pairs is examined for local excesses or deficits that are inconsistent with the Standard Model predictions. No evidence for a top quark pair resonance is found, and 95% confidence-level limits on the production rate are determined for massive states in benchmark models. The upper limits on the cross-section times branching ratio of a narrow Z' boson decaying to top pairs range from 4.2 pb to 0.03 pb for resonance masses from 0.4 TeV to 3.0 TeV. A narrow leptophobic topcolour Z' boson with mass below 1.8 TeV is excluded. Upper limits are set on the cross-section times branching ratio for a broad colour-octet resonance with Γ/m = 15% decaying to \( t\overline{t} \). These range from 4.8 pb to 0.03 pb for masses from 0.4 TeV to 3.0 TeV. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.2 TeV.
A search for the decays of the Higgs and Z bosons to J/psi gamma and Upsilon(nS) gamma (n=1,2,3) is performed with pp collision data samples corresponding to integrated luminosities of up to 20.3 ...fb-1 collected at s=8 TeV with the ATLAS detector at the CERN Large Hadron Collider. No significant excess of events is observed above expected backgrounds and 95% C.L. upper limits are placed on the branching fractions. In the J/psi gamma final state the limits are 1.5x10-3 and 2.6x10-6 for the Higgs and Z boson decays, respectively, while in the Upsilon(1S,2S,3S) gamma final states the limits are (1.3,1.9,1.3)x10-3 and (3.4,6.5,5.4)x10-6, respectively.
Searches are performed for resonant and nonresonant Higgs boson pair production in the gamma gamma bb super(-) final 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. 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 arrow right hh resonance ranges between 0.7 and 3.5 pb as a function of the resonance mass.
Many extensions of the Standard Model predict the existence of charged heavy long-lived particles, such as R-hadrons or charginos. These particles, if produced at the Large Hadron Collider, should be ...moving non-relativistically and are therefore identifiable through the measurement of an anomalously large specific energy loss in the ATLAS pixel detector. Measuring heavy long-lived particles through their track parameters in the vicinity of the interaction vertex provides sensitivity to metastable particles with lifetimes from 0.6 ns to 30 ns. A search for such particles with the ATLAS detector at the Large Hadron Collider is presented, based on a data sample corresponding to an integrated luminosity of 18.4 fb–1 of pp collisions at √s = 8 TeV. No significant deviation from the Standard Model background expectation is observed, and lifetime-dependent upper limits on R-hadrons and chargino production are set. Gluino R-hadrons with 10 ns lifetime and masses up to 1185 GeV are excluded at 95 % confidence level, and so are charginos with 15 ns lifetime and masses up to 482 GeV.
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