Study of Characteristics of the Quasi-spherical Measurement Modules of the Cherenkov Water Calorimeter NEVOD

AbstractThe use of quasi-spherical modules with several PMTs with flat photocathodes in Cherenkov water detectors is discussed. Properties of the response of such modules are examined. The characteristics of the quasi-spherical module with six PMTs that is used in the Cherenkov water calorimeter NEVOD are considered. The results of studying the isotropy of the amplitude response of this module and the quality of reconstruction of light direction with a single module and with a group of modules are demonstrated

Two-temperature relaxation and melting after absorption of femtosecond laser pulse

The theory and experiments concerned with the electron-ion thermal relaxation and melting of overheated crystal lattice constitute the subject of this paper. The physical model includes two-temperature equation of state, many-body interatomic potential, the electron-ion energy exchange, electron thermal conductivity, and optical properties of solid, liquid, and two phase solid-liquid mixture. Two-temperature hydrodynamics and molecular dynamics codes are used. An experimental setup with pump-probe technique is used to follow evolution of an irradiated target with a short time step 100 fs between the probe femtosecond laser pulses. Accuracy of measurements of reflection coefficient and phase of reflected probe light are ~1% and \sim 1\un{nm}, respectively. It is found that, {\it firstly}, the electron-electron collisions make a minor contribution to a light absorbtion in solid Al at moderate intensities; {\it secondly}, the phase shift of a reflected probe results from heating of ion subsystem and kinetics of melting of Al crystal during 0 where $t$ is time delay between the pump and probe pulses measured from the maximum of the pump; {\it thirdly} the optical response of Au to a pump shows a marked contrast to that of Al on account of excitation of \textit{d}-electronsComment: 6th International Conference on Photo-Excited Processes and Applications 9-12 Sep 2008, Sapporo, Japan, http://www.icpepa6.com, the contributed paper will be published in Applied Surface Science(2009

Flux pinning and vortex dynamics in MgB₂ doped with TiO₂ and SiC inclusions

The mixed-state superconducting properties of bulk MgB₂ + 2 at.% TiO₂ and + 8 at.% SiC, prepared by the in situ solid state reaction, have been investigated. The analysis on the mixed-state parameters, such as the upper critical field, the coherence length and the Ginzburg–Landau parameter, proves that the MgB₂ + 2 at.% TiO₂ is a high-к type-II superconductor in the dirty limit while the MgB₂ + 8 at.% SiC corresponds to that in the moderately clean limit. It was shown that the anisotropic grain-boundary pinning is realized in the fine-grained doped MgB₂ polycrystals rather than the electron scattering one. The field-cooled temperature dependences of magnetic moment exhibit a transition of the samples to the paramagnetic state at certain applied magnetic fields, which is treated as manifestation of the paramagnetic Meissner effect. The experimental results are discussed on the base of modern theoretical approaches

Evidence for non-Dzyaloshinskii–Moriya ferromagnetism in epitaxial BiFeO₃ films

BiFeO₃ films have been prepared by dc magnetron sputtering on LaAlO₃ (001) single-crystalline substrate. X-ray diffraction analysis and high-resolution electron-microscopy study reveal that the films have a highly coriented orthorhombic crystal structure. It was found that the magnetic properties of the BiFeO₃ films are typical for the ensemble of interacting superparamagnetic clusters rather than for the Dzyaloshinskii–Moriya weak ferromagnet. Appearance of the extrinsic nanoscale superparamagnetic clusters is explained by the oxygen deficiency in certain regions of the film, where the ferromagnetic ordering is realized through the double-exchange mechanism by Zener

Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2

We present a precise measurement of the deuteron longitudinal spin asymmetry A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1 GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured A_1^d and g_1^d are found to be consistent with zero in the whole range of x.Comment: 17 pages, 10 figure

Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs

We present a determination of the gluon polarization Delta G/G in the nucleon, based on the helicity asymmetry of quasi-real photoproduction events, Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV polarized muon beam scattered on a polarized 6-LiD target. The helicity asymmetry for the selected events is = 0.002 +- 0.019(stat.) +- 0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3 (GeV}/c)^2.Comment: 10 pages, 3 figure

The Deuteron Spin-dependent Structure Function g1d and its First Moment

We present a measurement of the deuteron spin-dependent structure function g1d based on the data collected by the COMPASS experiment at CERN during the years 2002-2004. The data provide an accurate evaluation for Gamma_1^d, the first moment of g1d(x), and for the matrix element of the singlet axial current, a0. The results of QCD fits in the next to leading order (NLO) on all g1 deep inelastic scattering data are also presented. They provide two solutions with the gluon spin distribution function Delta G positive or negative, which describe the data equally well. In both cases, at Q^2 = 3 (GeV/c)^2 the first moment of Delta G is found to be of the order of 0.2 - 0.3 in absolute value.Comment: fits redone using MRST2004 instead of MRSV1998 for G(x), correlation matrix adde

The COMPASS Experiment at CERN

The COMPASS experiment makes use of the CERN SPS high-intensitymuon and hadron beams for the investigation of the nucleon spin structure and the spectroscopy of hadrons. One or more outgoing particles are detected in coincidence with the incoming muon or hadron. A large polarized target inside a superconducting solenoid is used for the measurements with the muon beam. Outgoing particles are detected by a two-stage, large angle and large momentum range spectrometer. The setup is built using several types of tracking detectors, according to the expected incident rate, required space resolution and the solid angle to be covered. Particle identification is achieved using a RICH counter and both hadron and electromagnetic calorimeters. The setup has been successfully operated from 2002 onwards using a muon beam. Data with a hadron beam were also collected in 2004. This article describes the main features and performances of the spectrometer in 2004; a short summary of the 2006 upgrade is also given.Comment: 84 papes, 74 figure