15,621 research outputs found

    A high yield neutron target

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    Target, in cylinder form, rotates rapidly in front of beam. Titanium tritide film is much thicker than range of accelerated deutron. Sputtering electrode permits full use of thick film. Stream of high-velocity coolant provides efficient transfer of heat from target

    Strangeness Saturation: Dependence on System-Size, Centrality and Energy

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    The dependence of the strangeness saturation factor on the system size, centrality and energy is studied in relativistic heavy-ion collisions.Comment: contribution for Proc. 19th Winter Workshop on Nuclear Dynamics, Breckenridge, February 8-15, 200

    Photonic measurements of the longitudinal expansion dynamics in Heavy-Ion collisions

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    Due to the smallness of the electromagnetic coupling, photons escape from the hot and dense matter created in an heavy-ion collision at all times, in contrast to hadrons which are predominantly emitted in the final freeze-out phase of the evolving system. Thus, the thermal photon yield carries an imprint from the early evolution. We suggest how this fact can be used to gain information about where between the two limiting cases of Bjorken (boost-invariant expansion) and Landau (complete initial stopping and re-expansion) hydrodynamics the actual evolution can be found. We argue that both the rapidity dependence of the photon yield and photonic HBT radii are capable of answering this question.Comment: 10 pages, 3 figure

    Measurement of macroscopic plasma parameters with a radio experiment: Interpretation of the quasi-thermal noise spectrum observed in the solar wind

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    The ISEE-3 SBH radio receiver has provided the first systematic observations of the quasi-thermal (plasma waves) noise in the solar wind plasma. The theoretical interpretation of that noise involves the particle distribution function so that electric noise measurements with long antennas provide a fast and independent method of measuring plasma parameters: densities and temperatures of a two component (core and halo) electron distribution function have been obtained in that way. The polarization of that noise is frequency dependent and sensitive to the drift velocity of the electron population. Below the plasma frequency, there is evidence of a weak noise spectrum with spectral index -1 which is not yet accounted for by the theory. The theoretical treatment of the noise associated with the low energy (thermal) proton population shows that the moving electrical antenna radiates in the surrounding plasma by Carenkov emission which becomes predominant at the low frequencies, below about 0.1 F sub P

    Flow induced ultrasound scattering: experimental studies

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    Sound scattering by a finite width beam on a single rigid body rotation vortex flow is detected by a linear array of transducers (both smaller than a flow cell), and analyzed using a revised scattering theory. Both the phase and amplitude of the scattered signal are obtained on 64 elements of the detector array and used for the analysis of velocity and vorticity fields. Due to averaging on many pulses the signal-to-noise ratio of the phases difference in the scattered sound signal can be amplified drastically, and the resolution of the method in the detection of circulation, vortex radius, vorticity, and vortex location becomes comparable with that obtained earlier by time-reversal mirror (TRM) method (P. Roux, J. de Rosny, M. Tanter, and M. Fink, {\sl Phys. Rev. Lett.} {\bf 79}, 3170 (1997)). The revised scattering theory includes two crucial steps, which allow overcoming limitations of the existing theories. First, the Huygens construction of a far field scattering signal is carried out from a signal obtained at any intermediate plane. Second, a beam function that describes a finite width beam is introduced, which allows using a theory developed for an infinite width beam for the relation between a scattering amplitude and the vorticity structure function. Structure functions of the velocity and vorticity fields deduced from the sound scattering signal are compared with those obtained from simultaneous particle image velocimetry (PIV) measurements. Good quantitative agreement is found.Comment: 14 pages, 23 figures. accepted for publication in Phys. Fluids(June issue

    Heavy-ion physics with the ATLAS detector at the LHC

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    First results on jet, Jψ and Z production are presented from the first lead-lead run at the LHC, using the ATLAS detector. The transverse energies of opposed dijets are observed to show greater asymmetry with increasing event centrality, something not observed in proton-proton collisions. This may point to an interpretation in terms of strong jet energy loss in a hot, dense medium. Also, using the ATLAS muon spectrometer, a centrality-dependent suppression has been observed in the yield of J/ψ mesons. It is found to be qualitatively similar to the trends observed at previous, lower-energy experiments. The relative yields of Z bosons as a function of centrality are also presented, although the low statistics precludes any strong conclusions. These results provide a first look at the modification of high-pT processes in heavy-ion collisions at the highest-available beam energy
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