Nanosized patterns as reference structures for macroscopic transport properties and vortex phases in YBCO films

This paper studies the striking correlation between nanosized structural patterns in YBCO films and macroscopic transport current. A nanosized network of parallel Josephson junctions laced by insulating dislocations is almost mimicking the grain boundary structural network. It contributes to the macroscopic properties and accounts for the strong intergranular pinning across the film in the intermediate temperature range. The correlation between the two networks enables to find out an outstanding scaling law in the (Jc,B) plane and to determine meaningful parameters concerning the matching between the vortex lattice and the intergranular defect lattice. Two asymptotic behaviors of the pinning force below the flux flow regime are checked: the corresponding vortex phases are clearly individuated.Comment: 4 pages, 4 figure

Screening magnetic fields by a superconducting disk: a simple model

We introduce a simple approach to evaluate the magnetic field distribution around superconducting samples, based on the London equations; the elementary variable is the vector potential. This procedure has no adjustable parameters, only the sample geometry and the London length, $\lambda$, determine the solution. The calculated field reproduces quantitatively the measured induction field above MgB$_2$ disks of different diameters, at 20K and for applied fields lower than 0.4T. The model can be applied if the flux line penetration inside the sample can be neglected when calculating the induction field distribution outside the superconductor. Finally we show on a cup-shape geometry how one can design a magnetic shield satisfying a specific constraint

A new apparatus for deep patterning of beam sensitive targets by means of high-energy ion beam

The paper reports on a high precision equipment designed to modify over 3-dimensions (3D) by means of high-energy gold ions the local properties of thin and thick films. A target-moving system aimed at creating patterns across the volume is driven by an x-y writing protocol that allows one to modify beam sensitive samples over micrometer-size regions of whatever shape. The apparatus has a mechanical resolution of 15 nm. The issue of the local fluence measurement has been particularly addressed. The setup has been checked by means of different geometries patterned on beam sensitive sheets as well as on superconducting materials. In the last case the 3D modification consists of amorphous nanostructures. The nanostructures create zones with different dissipative properties with respect to the virgin regions. The main analysis method consists of magneto-optical imaging that provides local information on the electrodynamics of the modified zones. Features typical of non-linear current flow hint at which pattern geometry is more functional to applications in the framework of nanostructures across superconducting films.Comment: 7 page

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

Combined search for the quarks of a sequential fourth generation

Results are presented from a search for a fourth generation of quarks produced singly or in pairs in a data set corresponding to an integrated luminosity of 5 inverse femtobarns recorded by the CMS experiment at the LHC in 2011. A novel strategy has been developed for a combined search for quarks of the up and down type in decay channels with at least one isolated muon or electron. Limits on the mass of the fourth-generation quarks and the relevant Cabibbo-Kobayashi-Maskawa matrix elements are derived in the context of a simple extension of the standard model with a sequential fourth generation of fermions. The existence of mass-degenerate fourth-generation quarks with masses below 685 GeV is excluded at 95% confidence level for minimal off-diagonal mixing between the third- and the fourth-generation quarks. With a mass difference of 25 GeV between the quark masses, the obtained limit on the masses of the fourth-generation quarks shifts by about +/- 20 GeV. These results significantly reduce the allowed parameter space for a fourth generation of fermions.Comment: Replaced with published version. Added journal reference and DO

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum