A search for the fourth SM family quarks at Tevatron

It is shown that the fourth standard model (SM) family quarks can be observed at the Fermilab Tevatron if their anomalous interactions with known quarks have sufficient strength.Comment: 7 pages, 2 tables, 4 figure

Adsorption of Pt and bimetallic PtAu clusters on the partially reduced rutile (110) TiO 2 surface: A first-principles study

An extensive study of the adsorption of small Pt n (n = 1-8) and bimetallic Pt 2Au m (m = 1-5) clusters on the partially reduced rutile (110) TiO 2 surface has been performed via total energy pseudopotential calculations based on density functional theory. Structures, energetics, and electronic properties of adsorbed Pt n and Pt 2Au m clusters have been determined. The surface oxygen vacancy site has been found to be the nucleation center for the growth of Pt clusters. These small Pt clusters strongly interact with the partially reduced surface and prefer to form planar structures for n = 1-6 since the cluster-substrate interaction governs the cluster growth at low Pt coverage. We found a planar-to-three-dimensional structural transition at n = 7 for the formation of Pt n clusters on the reduced TiO 2 surface. GGA+U calculations have also been performed to get a reasonable description of the reduced oxide surface. We observed significant band gap narrowing upon surface-Pt n cluster interaction which leads to the formation of gap localized Pt states. In the case of bimetallic Pt-Au clusters, Au m clusters have been grown on the Pt 2-TiO 2 surface. The previously adsorbed Pt dimer at the vacancy site of the reduced surface acts as a clustering center for Au atoms. The presence of the Pt dimer remarkably enhances the binding energy and limits the migration of Au atoms on the titania surface. The charge state of both individual atoms and clusters has been obtained from the Bader charge analysis, and it has been found that charge transfer among the Pt atoms of Pt n clusters and the metal oxide surface is stronger compared to that of Au clusters and the Pt 2-TiO 2 system. © 2012 American Chemical Society

Search for supersymmetry in events with large missing transverse momentum, jets, and at least one tau lepton in 20 fb−1 of √s= 8 TeV proton-proton collision data with the ATLAS detector

© 2014, The Author(s). A search for supersymmetry (SUSY) in events with large missing transverse momentum, jets, at least one hadronically decaying tau lepton and zero or one additional light leptons (electron/muon), has been performed using 20.3fb−1of proton-proton collision data at √ s= 8 TeV recorded with the ATLAS detector at the Large Hadron Collider. No excess above the Standard Model background expectation is observed in the various signal regions and 95% confidence level upper limits on the visible cross section for new phenomena are set. The results of the analysis are interpreted in several SUSY scenarios, significantly extending previous limits obtained in the same final states. In the framework of minimal gauge-mediated SUSY breaking models, values of the SUSY breaking scale Λ below 63 TeV are excluded, independently of tan β. Exclusion limits are also derived for an mSUGRA/CMSSM model, in both the R-parity-conserving and R-parity-violating case. A further interpretation is presented in a framework of natural gauge mediation, in which the gluino is assumed to be the only light coloured sparticle and gluino masses below 1090 GeV are excluded