Results of a study of the substructure of the highest transverse momentum (pT) jets observed by the CDF collaboration are presented. Events containing at least one jet with pT > 400 GeV/c in a sample corresponding to an integrated luminosity of 5.95
inverse fb, collected in 1.96 TeV proton-antiproton collisions at the Fermilab Tevatron collider, are selected. A study of the jet mass, angularity, and planar-flow distributions is presented, and the measurements are compared with predictions of perturbative quantum chromodynamics. A search for boosted top-quark production is also described, leading to a 95% confidence level upper limit of 38 fb on the production cross section of top quarks with pT > 400 GeV/c.
We briefly review the concept and properties of the Thick GEM (THGEM); it is a robust, high-gain gaseous electron multiplier, manufactured economically by standard printed-circuit drilling and etching technology. Its operation and structure resemble
that of GEMs but with 5 to 20-fold expanded dimensions. The millimeter-scale hole-size results in good electron transport and in large avalanche-multiplication factors, e.g. reaching 10^7 in double-THGEM cascaded single-photoelectron detectors. The multipliers material, parameters and shape can be application-tailored; it can operate practically in any counting gas, including noble gases, over a pressure range spanning from 1 mbar to several bars; its operation at cryogenic (LAr) conditions was recently demonstrated. The high gain, sub-millimeter spatial resolution, high counting-rate capability, good timing properties and the possibility of industrial production capability of large-area robust detectors, pave ways towards a broad spectrum of potential applications; some are discussed here in brief.
We present the results of our recent studies on a Thick Gas Electron Multiplier (THGEM)-based imaging detector prototype. It consists of two 100x100 mm^2 THGEM electrodes in cascade, coupled to a resistive anode. The event location is recorded with a
2D double-sided readout electrode equipped with discrete delay-lines and dedicated electronics. The THGEM electrodes, produced by standard printed-circuit board and mechanical drilling techniques, a 0.4 mm thick with 0.5 mm diameter holes spaced by 1 mm. Localization resolutions of about 0.7 mm (FWHM) were measured with soft x-rays, in a detector operated with atmospheric-pressure Ar/CH4; good linearity and homogeneity were achieved. We describe the imaging-detector layout, the resistive-anode 2D readout system and the imaging properties. The THGEM has numerous potential applications that require large-area imaging detectors, with high-rate capability, single-electron sensitivity and moderate (sub-mm) localization resolution.
We present the results of our recent studies of a Thick Gaseous Electron Multiplier (THGEM)-based detector, operated in Ar, Xe and Ar:Xe (95:5) at various gas pressures. Avalanche-multiplication properties and energy resolution were investigated with
soft x-rays for different detector configurations and parameters. Gains above 10E4 were reached in a double-THGEM detector, at atmospheric pressure, in all gases, in almost all the tested conditions; in Ar:Xe (95:5) similar gains were reached at pressures up to 2 bar. The energy resolution dependence on the gas, pressure, hole geometry and electric fields was studied in detail, yielding in some configurations values below 20% FWHM with 5.9 keV x-rays.
