Laser shadow and interferometric investigation of the structure and dynamics of plasma in PF-3 facility

The work presents the laser investigation of a plasma focus discharge in neon. This investigation was done in connection with the recently discussed possibility of the use of such type of discharges for the creation of the soft X-ray source and its application for the compression of the solid targets (liners). Some features of a plasma focus discharge in 2.8 MJ Plasma Focus such as a complicated structure of current-plasma sheath (CPS), its relation to soft X-ray (SXR) pulse emitted from a pinching region were studied by developed laser diagnostics.У роботі представлене лазерне дослідження плазмово-фокусного розряду в неоні на установці ПФ-3. Дослідження були виконані в зв'язку з обговорюваною останнім часом можливістю використання такого типу розрядів для створення могутніх джерел м'якого рентгенівського випромінювання і їх застосування для стиску твердих мішеней (лайнерів). Деякі особливості плазмово-фокусного розряду в установці ПФ-3 такі, як складна структура струмо-плазмової оболонки і її зв'язок із властивостями імпульсу м'якого рентгенівського випромінювання, випромінюваного з області пінчування плазми, досліджені за допомогою розробленої лазерної діагностики.В работе представлено лазерное исследование плазмофокусного разряда в неоне на установке ПФ-3. Исследования были выполнены в связи с обсуждаемой в последнее время возможностью использования такого типа разрядов для создания мощных источников мягкого рентгеновского излучения и применения их для сжатия твердых мишеней (лайнеров). Некоторые особенности плазмофокусного разряда в установке ПФ-3 такие, как сложная структура токово-плазменной оболочки и ее связь со свойствами импульса мягкого рентгеновского излучения, излучаемого из области пинчевания плазмы, исследованы с помощью разработанной лазерной диагностики

Role of dislocations in formation of ohmic contacts to heavily doped n-Si

We present experimental results concerning a high density of structural defects (in particular, dislocations) in the near-contact region of heavily doped n-silicon. They appear in the course of firing Au Pd Ti Pd -Si n ohmic contact at 450С for 10 min in a vacuum of ~10 Pa⁻⁴ . These defects lead to appearance of metal shunts that determine the current flow mechanism in these ohmic contacts. The calculated and experimental temperature dependences of contact resistivity, ρс(Т), are in good agreement. It is shown that ρс increases with temperature. This is characteristic of a model of ohmic contacts with a high dislocation density in the near-contact region of semiconducto

On a feature of temperature dependence of contact resistivity for ohmic contacts to n-Si with an n⁺ -n doping step

We present both theoretical and experimental temperature dependences of contact resistivity ρс(Т) for ohmic contacts to the silicon n⁺ -n-structures whose n⁺ -layer was formed using phosphorus diffusion or ion implantation. The ρс(Т) dependence was measured in the 125–375 K temperature range with the transmission line method, with allowance made for conduction in both the n⁺ -layer and n⁺ -n doping step

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC

Measurements of inclusive jet suppression in heavy ion collisions at the LHC provide direct sensitivity to the physics of jet quenching. In a sample of lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the anti-kt algorithm with values for the distance parameter that determines the nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp. Jet production is found to be suppressed by approximately a factor of two in the 10% most central collisions relative to peripheral collisions. Rcp varies smoothly with centrality as characterized by the number of participating nucleons. The observed suppression is only weakly dependent on jet radius and transverse momentum. These results provide the first direct measurement of inclusive jet suppression in heavy ion collisions and complement previous measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables, submitted to Physics Letters B. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters