700 research outputs found

    Parton Production Via Vacuum Polarization

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    We discuss the production mechanism of partons via vacuum polarization during the very early, gluon dominated phase of an ultrarelativistic heavy-ion collision in the framework of the background field method of quantum chromodynamics.Comment: 3 pages, Latex, 3 figures (eps), to be published in JPhysG, SQM2001 proceeding

    Fluid Dynamics of Relativistic Quantum Dust

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    The microscopic transport equations for free fields are solved using the Schwinger function. Thus, for general initial conditions, the evolution of the energy-momentum tensor is obtained, incorporating the quantum effects exactly. The result for relativistic fermions differs from classical hydrodynamics, which is illustrated for Landau and Bjorken type initial conditions in this model of exploding primordial matter. Free fermions behave like classical dust concerning hydrodynamic observables. However, quantum effects which are present in the initial state are preserved.Comment: 5 pages; LaTe

    Low-noise monolithic bipolar front-end for silicon drift detectors

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    Abstract A very low noise, 32-channel preamplifier/shaper chip has been designed for the analogue readout of silicon detectors. The circuit has been optimized in view of the operation of silicon drift detectors, which have very low capacitance and produce gaussian signals of σ of few tens of ns. The chip (OLA) has been designed and manufactured using the SHPi full-custom bipolar process by Tektronix. Each channel is composed by a preamplifier, a shaper and a symmetrical line driver, which allows to drive either a positive and a negative single ended output separately on 50 Ω impedance or a differential twisted pair. The intrinsic peaking time of the circuit is ∌60 ns , and the noise is below 250 electrons at zero input load capacitance. The power consumption is 2 mW/channel, mostly due to the output driver

    Beam test results of the irradiated Silicon Drift Detector for ALICE

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    The Silicon Drift Detectors will equip two of the six cylindrical layers of high precision position sensitive detectors in the ITS of the ALICE experiment at LHC. In this paper we report the beam test results of a SDD irradiated with 1 GeV electrons. The aim of this test was to verify the radiation tolerance of the device under an electron fluence equivalent to twice particle fluence expected during 10 years of ALICE operation.Comment: 6 pages,6 figures, to appear in the proceedings of International Workshop In high Multiplicity Environments (TIME'05), 3-7 October 2005, Zurich,Switzerlan

    Measurement of the cosmic ray hadron spectrum up to 30 TeV at mountain altitude: the primary proton spectrum

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    The flux of cosmic ray hadrons at the atmospheric depth of 820 g/cm^2 has been measured by means of the EAS-TOP hadron calorimeter (Campo Imperatore, National Gran Sasso Laboratories, 2005 m a.s.l.). The hadron spectrum is well described by a single power law : S(E_h) = (2.25 +- 0.21 +- 0.34(sys)) 10^(-7)(E_h/1000)^(-2.79 +- 0.05) m^(-2) s^(-1) sr^(-1) GeV^(-1) over the energy range 30 GeV-30 TeV. The procedure and the accuracy of the measurement are discussed. The primary proton spectrum is derived from the data by using the CORSIKA/QGSJET code to compute the local hadron flux as a function of the primary proton spectrum and to calculate and subtract the heavy nuclei contribution (basing on direct measurements). Over a wide energy range E_0 = 0.5-50 TeV its best fit is given by a single power law : S(E_0) = (9.8 +- 1.1 +- 1.6(sys)) 10^(-5) (E_0/1000)^(-2.80 +- 0.06) m^(-2) s^(-1) sr^(-1) GeV^(-1). The validity of the CORSIKA/QGSJET code for such application has been checked using the EAS-TOP and KASCADE experimental data by reproducing the ratio of the measured hadron fluxes at the two experimental depths (820 and 1030 g/cm^2 respectively) at better than 10% in the considered energy range.Comment: 16 pages, 9 figures, accepted for publication in Astroparticle Physic

    The silicon Multiplicity Detector for the NA50 experiment

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    Abstract The operation and performance of the silicon strip Multiplicity Detector in the heavy-ion experiment NA50 at CERN are presented together with a selection of physics results. The main features of the detector are high speed (50 MHz sampling frequency), high granularity (more than 13,000 strips), and good radiation resistance. The detector provided a measurement of event centrality in Pb–Pb collisions, as well as target identification and the measurement of charged particle pseudorapidity distributions as a function of centrality

    Radiation damage of silicon strip detectors in the NA50 experiment

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    Abstract During operation of the multiplicity detector in the NA50 experiment the single sided AC-coupled p-on-n silicon strip detectors were exposed to charged particle fluences up to 10 14 eq n/cm 2 and ionising doses up to 20 Mrad, with a very non-uniform radiation spatial distribution. Radiation effects in the detectors observed during the '96 lead ion run as well as results of the post-run measurements are presented in this paper

    Phase Space Description of the Leading Order Quark and Gluon Production from a Space-Time Dependent Chromofield

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    We derive source terms for the production of quarks and gluons from the QCD vacuum in the presence of a space-time dependent external chromofield A_{cl} to the order of S^{(1)}. We found that the source terms for the parton production processes A_{cl} -> q\bar{q} and A_{cl},A_{cl}A_{cl} -> gg also include the annihilation processes q\bar{q} -> A_{cl} and gg -> A_{cl},A_{cl}A_{cl}. The source terms we derive are applicable for the description of the production of partons with momentum p larger rhan gA which itself must be larger than \Lambda_{QCD}. We observe that these source terms for the production of partons from a space-time dependent chromofield can be used to study the production and equilibration of the quark-gluon plasma during the very early stages of an ultrarelativistic heavy-ion collision.Comment: 30 pages latex (single spaced), 7 eps figures, Revised Version, To appear in Physical Review

    Analysis of radiation effects on silicon strip detectors in the NA50 experiment

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    Abstract During the operation of the Multiplicity Detector in the NA50 experiment the single sided AC-coupled p-on-n silicon strip detectors were exposed to charged particle fluences resulting in an equivalent 1 MeV neutron fluence up to 10 14 eq. n/cm 2 and a total ionising dose up to 20 Mrad, with a very non-uniform radiation spatial distribution. In this paper detailed analysis of radiation effects observed on the detectors during the 1996 lead ion run as well as results of measurements performed after the run are presented
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