Low mass Higgs boson searches in b¯b or ττ channels at CMS

The most probable decay for a light Higgs Boson Standard Model (mH < 135 GeV) is H → b¯b; the signal competes with background mostly due to multijet processes (QCD). The poster summarizes the analysis status with data sample corresponding to an integrated luminosity of about 4.7 fb −1, collected in 2011 by the Compact Muon Solenoid experiment during the Large Hadron Collider proton-proton collisions at a centre of mass energy √s = 7TeV. The Standard Model Higgs H, produced in association with a vector boson V , is studied in five different final states, where H → b¯b and the vector boson decays to charged leptons (e, μ) and neutrinos. The poster shows the resulting global limit on production cross section of Higgs boson and weak bosons, pp → VH + X. The poster also includes information on recent light Higgs boson searches studying the H → ττ decay. Such a final state is also important in the context of MSSM neutral Higgs boson searches

Effect of proton irradiation on the normal state low-energy excitations of Ba(Fe1−x_{1-x}Rhx_x)2_2As2_2 superconductors

We present a \asnmr Nuclear Magnetic Resonance (NMR) and resistivity study of the effect of 5.5 MeV proton irradiation on the optimal electron doped ($x=$ 0.068) and overdoped ($x=$ 0.107) Ba(Fe$_{1-x}$Rh$_x$)$_2$As$_2$ iron based superconductors. While the proton induced defects only mildly suppress the critical temperature and increase residual resistivity in both compositions, sizable broadening of the NMR spectra was observed in all the irradiated samples at low temperature. The effect is significantly stronger in the optimally doped sample where the Curie Weiss temperature dependence of the line width suggests the onset of ferromagnetic correlations coexisting with superconductivity at the nanoscale. 1/T$_2$ measurements revealed that the energy barrier characterizing the low energy spin fluctuations of these compounds is enhanced upon proton irradiation, suggesting that the defects are likely slowing down the fluctuations between ($0,\pi)$ and ($\pi$,0) nematic ground states.Comment: 9 pages, 9 figure

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

Dual curing systems based on UV curing and alkoxy-silane groups condensation

The use of dual curing systems was proposed in order to overcome some problems and unsatisfactory properties presented by UV curable coatings, mainly with respect to adhesion and mechanical properties. In these systems two types of functional groups are present, one sensitive to the radical curing reaction induced by UV radiation (generally acrylic d. b.) , the other suitable to react according to a different mechanism which is normally chosen among thermal curing processes, at high or room temperature, as well in the presence of epoxy or Isocyanate groups. The use of alkoxy-silane derivatives as coupling agents, mainly for glass fibers, is well known; the condensation reaction between the silanolic groups of the organic network and the ones on the glass surface yields very strong siloxane bonds. Moreover the use of these compour)d as adhesion promoters for metal substrates was reported in the literature. Therefore the study' of a dual curing system based on UV curing and alkoxy-silane groups condensation seems to be interesting In order to achieve particular film properties (e.g. adhesion on glass substrates) or to modify the network structure

Comprehensive Eliashberg analysis of microwave conductivity and penetration depth of K-, Co-, and P-substituted BaFe2As2

We report on the combined experimental and theoretical analysis of the microwave-frequency electromagnetic response of BaFe2As2single crystals with different substitutions: K in the Ba site (hole doping), Co in the Fe site (electron doping), and P in the As site (isovalent substitution). Measurements using a coplanar resonator technique lead to the experimental determination of the penetration depth and microwave conductivity as a function of temperature. The whole set of data is analyzed within a self-consistent three-bands±-wave Eliashberg approach, able to account for all the main observed features in the different properties. Besides the validation of the model itself, the comparison between experiment and theory allows discussing the possible role of the Fe-As planes in defining the superconducting properties of these compounds, the relevance of coherence effects, and the presence of nodes in the superconducting order parameter

A pulsed-Laser Rb atomic frequency standard for GNSS applications

We present the results of 10 years of research related to the development of a Rubidium vapor cell clock based on the principle of pulsed optical pumping (POP). Since in the pulsed approach, the clock operation phases take place at different times, this technique demonstrated to be very effective in curing several issues affecting traditional Rb clocks working in a continuous regime, like light shift, with a consequent improvement of the frequency stability performances. We describe two laboratory prototypes of POP clock, both developed at INRIM. The first one achieved the best results in terms of frequency stability: an Allan deviation of σy(τ) = 1.7 × 10−13 τ−1/2, being τ the averaging time, has been measured. In the prospect of a space application, we show preliminary results obtained with a second more recent prototype based on a loaded cavity-cell arrangement. This clock has a reduced size and exhibited an Allan deviation of σy(τ) = 6 × 10−13 τ−1/2, still a remarkable result for a vapor cell device. In parallel, an ongoing activity performed in collaboration with Leonardo S.p.A. and aimed at developing an engineered space prototype of the POP clock is finally mentioned. Possible issues related to space implementation are also briefly discussed. On the basis of the achieved results, the POP clock represents a promising technology for future GNSSs

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

Disorder-Driven Transition from s(+/-) to s(+ +) Superconducting Order Parameter in Proton Irradiated Ba(Fe1-xRhx)(2)As-2 Single Crystals

Microwave measurements of the London penetration depth and critical temperature T c were used to show evidence of a disordered-driven transition from s ± to s + + order parameter symmetry in optimally doped Ba ( Fe 1 − x Rh x ) 2 As 2 single crystals, where disorder was induced by means of 3.5 MeV proton irradiation. Signatures of such a transition, as theoretically predicted [V. D. Efremov et al., Phys. Rev. B 84, 180512(R) (2011)], are found as a drop in the low-temperature values of the London penetration depth and a virtually disorder-independent superconducting T c . We show how these experimental observations can be described by multiband Eliashberg calculations in which the effect of disorder is accounted for in a suitable way. To this aim, an effective two-band approach is adopted, allowing us to treat disorder in a range between the Born approximation and the unitary limit

Twofold role of columnar defects in iron based superconductors

We report on the introduction of columnar defects in Ba1−x K x Fe2As2 and BaFe2(As1−x P x )2 single crystals via 1.2 GeV Pb irradiation. Scanning transmission electron microscopy analysis proves the formation of continuous defects along the ion tracks, with a diameter of about 3 nm, and a planar density compatible with the irradiation fluence. The twofold role of such defects, i.e. as pair breakers as well as pinning centers, is investigated by a microwave technique, allowing us to determine critical temperature T c , surface impedance and penetration depth λ L , and by magneto-optical imaging and superconducting quantum interference device magnetometry to evaluate the critical current density J c . The decrease of T c is quite modest and, together with λ L modifications, testifies the increase of pair-breaking scattering following irradiation. The dependence of J c on irradiation dose and temperature is due to the pinning landscape induced by the columnar defects, and shows the existence of an optimal irradiation dose to enhance the critical current