Search for resonances decaying into top-quark pairs using fully hadronic decays in pp collisions with ATLAS at sqrts=7 TeV

A search for resonances produced in 7 TeV proton-proton collisions and decaying into top-quark pairs is described. In this Letter events where the top-quark decay produces two massive jets with large transverse momenta recorded with the ATLAS detector at the Large Hadron Collider are considered. Two techniques that rely on jet substructure are used to separate top-quark jets from those arising from light quarks and gluons. In addition, each massive jet is required to have evidence of an associated bottom-quark decay. The data are consistent with the Standard Model, and limits can be set on the production cross section times branching fraction of a Z' boson and a Kaluza-Klein gluon resonance. These limits exclude, at the 95% credibility level, Z' bosons with masses 0.70-1.00 TeV as well as 1.28-1.32 TeV and Kaluza-Klein gluons with masses 0.70-1.62 TeV.

A search for ttbar resonances in the lepton plus jets final state with ATLAS using 4.7 fb⁻¹ of collisions at sqrt(s) = 7 TeV

A search for new particles that decay into top quark pairs (t (t) over bar) is performed with the ATLAS experiment at the LHC using an integrated luminosity of 4.7 fb(-1) of proton-proton (pp) collision data collected at a center-of-mass energy root s = 7 TeV. In the t (t) over bar) -> WbWb decay, the lepton plus jets final state is used, where one W boson decays leptonically and the other hadronically. The t (t) over bar) system is reconstructed using both small-radius and large-radius jets, the latter being supplemented by a jet substructure analysis. A search for local excesses in the number of data events compared to the Standard Model expectation in the t (t) over bar) invariant mass spectrum is performed. No evidence for a t (t) over bar) resonance is found and 95% credibility-level limits on the production rate are determined for massive states predicted in two benchmark models. The upper limits on the cross section times branching ratio of a narrow Z' resonance range from 5.1 pb for a boson mass of 0.5 TeV to 0.03 pb for a mass of 3 TeV. A narrow leptophobic topcolor Z' resonance with a mass below 1.74 TeV is excluded. Limits are also derived for a broad color-octet resonance with m 15.3%. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.07 TeV.

A search for high-mass resonances decaying to tau⁺ tau⁻ in pp collisions at sqrts=7 TeV with the ATLAS detector

This Letter presents a search for high-mass resonances decaying into tau(+)tau(-) final states using proton-proton collisions at root s = 7 TeV produced by the Large Hadron Collider. The data were recorded with the ATLAS detector and correspond to an integrated luminosity of 4.6 fb(-1). No statistically significant excess above the Standard Model expectation is observed; 95% credibility upper limits are set on the cross section times branching fraction of Z' resonances decaying into tau(+)tau(-) pairs as a function of the resonance mass. As a result, Z' bosons of the Sequential Standard Model with masses less than 1.40 TeV are excluded at 95% credibility.

Search for new resonances in Wѵ and ℤѵ final states in pp collisions at √s=8 TeV with the ATLAS detector

This Letter presents a search for new resonances decaying to final states with a vector boson produced in association with a high transverse momentum photon, Vγ, with V=W(→ℓν)or Z(→ℓ+ℓ−), where ℓ =e or μ. The measurements use 20.3fb−1 of proton–proton collision data at a center-of-mass energy of √s=8TeV recorded with the ATLAS detector. No deviations from the Standard Model expectations are found, and production cross section limits are set at 95% confidence level. Masses of the hypothetical aT and ωT states of a benchmark Low Scale Technicolor model are excluded in the ranges [275, 960] GeVand [200, 700] ∪[750, 890] GeV, respectively. Limits at 95% confidence level on the production cross section of a singlet scalar resonance decaying to Zγ final states have also been obtained for masses below 1180 GeV.

Search for Scalar Diphoton Resonances in the Mass Range 65-600 GeV with the ATLAS Detector in pp Collision Data at √s = 8 TeV

A search for scalar particles decaying via narrow resonances into two photons in the mass range 65–600 GeV is performed using 20.3  fb −1 of s √ =8  TeV pp collision data collected with the ATLAS detector at the Large Hadron Collider. The recently discovered Higgs boson is treated as a background. No significant evidence for an additional signal is observed. The results are presented as limits at the 95% confidence level on the production cross section of a scalar boson times branching ratio into two photons, in a fiducial volume where the reconstruction efficiency is approximately independent of the event topology. The upper limits set extend over a considerably wider mass range than previous searches.

Search for WZ resonances in the fully leptonic channel using pp collisions at √s = 8 TeV with the ATLAS detector

A search for resonant WZ production in the ℓνℓ′ℓ′ℓνℓ′ℓ′ (ℓ,ℓ′=e,μℓ,ℓ′=e,μ) decay channel using 20.3 fb−1 of View the MathML sources=8 TeVpp collision data collected by the ATLAS experiment at LHC is presented. No significant deviation from the Standard Model prediction is observed and upper limits on the production cross sections of WZ resonances from an extended gauge model W′W′ and from a simplified model of heavy vector triplets are derived. A corresponding observed (expected) lower mass limit of 1.52 (1.49) TeV is derived for the W′W′ at the 95% confidence level.

Search for high-mass dilepton resonances in pp collisions at √s=8 TeV with the ATLAS detector

The ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to dielectron or dimuon final states. Results are presented from an analysis of proton-proton (pp ) collisions at a center-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3  fb −1 in the dimuon channel. A narrow resonance with Standard Model Z couplings to fermions is excluded at 95% confidence level for masses less than 2.79 TeV in the dielectron channel, 2.53 TeV in the dimuon channel, and 2.90 TeV in the two channels combined. Limits on other model interpretations are also presented, including a grand-unification model based on the E 6 gauge group, Z ∗ bosons, minimal Z' models, a spin-2 graviton excitation from Randall-Sundrum models, quantum black holes, and a minimal walking technicolor model with a composite Higgs boson.

Visibility of lipid resonances in HR-MAS spectra of brain biopsies subject to spinning rate variation.

Lipid resonances from mobile lipids can be observed by (1)H NMR spectroscopy in multiple tissues and have also been associated with malignancy. In order to use lipid resonances as a marker for disease, a reference standard from a healthy tissue has to be established taking the influence of variable factors like the spinning rate into account. The purpose of our study was to investigate the effect of spinning rate variation on the HR-MAS pattern of lipid resonances in non-neoplastic brain biopsies from different regions and visualize polar and non-polar lipids by fluorescence microscopy using Nile Red staining. (1)H HR-MAS NMR spectroscopy demonstrated higher lipid peak intensities in normal sheep brain pure white matter biopsies compared to mixed white and gray matter biopsies and pure gray matter biopsies. High spinning rates increased the visibility particularly of the methyl resonances at 1.3 and the methylene resonance at 0.89ppm in white matter biopsies stronger compared to thalamus and brainstem biopsies, and gray matter biopsies. The absence of lipid droplets and presence of a large number of myelin sheaths observed in white matter by Nile Red fluorescence microscopy suggest that the observed lipid resonances originate from the macromolecular pool of lipid protons of the myelin sheath's plasma membranes. When using lipid contents as a marker for disease, the variable behavior of lipid resonances in different neuroanatomical regions of the brain and at variable spinning rates should be considered. The findings may open up interesting possibilities for investigating lipids in myelin sheaths.