1,112 research outputs found
The Angular Power Spectrum of Heavy Ion Collisions
Particles produced in heavy ion collisions carry information about
anisotropies present already in the early state of the system and play a
crucial role in understanding the Quark Gluon Plasma and its evolution. We
explore the angular power spectrum of particle multiplicities in such heavy ion
collisions to extract fluctuations in particle multiplicities on the surface a
sphere. Results are presented for Pb-Pb data at , extracted from the ALICE open data portal. We find that odd
modes of the power spectrum display a power-law behavior with corresponding
index , which is found to be close to unity. We also demonstrate that
the angular power spectrum allows us to extract accurately the flow
coefficients of non-central collisions
The Laser Calibration System of the ALICE Time Projection Chamber
A Large Ion Collider Experiment (ALICE) is the only experiment at the Large
Hadron Collider (LHC) dedicated to the study of heavy ion collisions. The Time
Projection Chamber (TPC) is the main tracking detector covering the pseudo
rapidity range . It is designed for a maximum multiplicity \dNdy =
8000. The aim of the laser system is to simulate ionizing tracks at predifined
positions throughout the drift volume in order to monitor the TPC response to a
known source. In particular, the alignment of the read-out chambers will be
performed, and variations of the drift velocity due to drift field
imperfections can be measured and used as calibration data in the physics data
analysis. In this paper we present the design of the pulsed UV laser and
optical system, together with the control and monitoring systems.Comment: 4 pages, 3 figure
The Laser of the ALICE Time Projection Chamber
The large TPC () of the ALICE detector at the CERN LHC was
commissioned in summer 2006. The first tracks were observed both from the
cosmic ray muons and from the laser rays injected into the TPC. In this article
the basic principles of operating the lasers are presented,
showing the installation and adjustment of the optical system and describing
the control system. To generate the laser tracks, a wide laser beam is split
into several hundred narrow beams by fixed micro-mirrors at stable and known
positions throughout the TPC. In the drift volume, these narrow beams generate
straight tracks at many angles. Here we describe the generation of the first
tracks and compare them with simulations.Comment: QM06 poster proceedings, 6 pages, 4 figure
Perspectives of Nuclear Physics in Europe: NuPECC Long Range Plan 2010
The goal of this European Science Foundation Forward Look into the future of Nuclear Physics is to bring together
the entire Nuclear Physics community in Europe to formulate a coherent plan of the best way to develop the field in
the coming decade and beyond.<p></p>
The primary aim of Nuclear Physics is to understand the origin, evolution, structure and phases of strongly interacting matter, which constitutes nearly 100% of the visible matter in the universe. This is an immensely important and challenging task that requires the concerted effort of scientists working in both theory and experiment, funding agencies, politicians and the public.<p></p>
Nuclear Physics projects are often “big science”, which implies large investments and long lead times. They need careful forward planning and strong support from policy makers. This Forward Look provides an excellent tool to achieve this. It represents the outcome of detailed scrutiny by Europe’s leading experts and will help focus the views of the scientific community on the most promising directions in the field and create the basis for funding agencies to provide adequate support.<p></p>
The current NuPECC Long Range Plan 2010 “Perspectives of Nuclear Physics in Europe” resulted from consultation
with close to 6 000 scientists and engineers over a period of approximately one year. Its detailed recommendations
are presented on the following pages. For the interested public, a short summary brochure has been produced to
accompany the Forward Look.<p></p>
Transverse Momentum Spectra in Au+Au and d+Au Collisions at =200 GeV and the Pseudorapidity Dependence of High p Suppression
We present spectra of charged hadrons from Au+Au and d+Au collisions at
GeV measured with the BRAHMS experiment at RHIC. The
spectra for different collision centralities are compared to spectra from collisions at the same energy scaled by the number of binary
collisions. The resulting ratios (nuclear modification factors) for central
Au+Au collisions at and evidence a strong suppression in
the high region (2 GeV/c). In contrast, the d+Au nuclear
modification factor (at ) exhibits an enhancement of the high
yields. These measurements indicate a high energy loss of the high
particles in the medium created in the central Au+Au collisions. The lack of
suppression in d+Au collisions makes it unlikely that initial state effects can
explain the suppression in the central Au+Au collisions.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Restoration of Isospin Symmetry in Highly Excited Nuclei
Explicit relations between the isospin mixing probability, the spreading
width of the Isobaric Analog State (IAS) and the
statistical decay width of the compound nucleus at finite excitation
energy, are derived by using the Feshbach projection formalism. The temperature
dependence of the isospin mixing probability is discussed quantitatively for
the first time by using the values of and of
calculated by means of microscopic models. It is shown that the
mixing probability remains essentially constant up to a temperature of the
order of 1 MeV and then decreases to about 1/4 of its zero temperature value,
at higher temperature than 3 MeV, due to the short decay time of the
compound system.Comment: 13 pages, 1 figure (PostScript file included). To appear in Phys.
Lett.
Rapidity Dependence of Charged Antiparticle-to-Particle Ratios in Au+Au Collisions at GeV
We present ratios of the numbers of charged antiparticles to particles
(pions, kaons and protons) in Au + Au collisions at GeV as
a function of rapidity in the range =0-3. While the particle ratios at
midrapidity are approaching unity, the and ratios
decrease significantly at forward rapidities. An interpretation of the results
within the statistical model indicates a reduction of the baryon chemical
potential from MeV at =3 to MeV at
=0.Comment: 4 pages, 4 figure
Behavior of the giant-dipole resonance in Sn and Pb at high excitation energ
The properties of the giant-dipole resonance (GDR) are calculated as a
function of excitation energy, angular momentum, and the compound nucleus
particle decay width in the nuclei Sn and Pb, and are compared
with recent experimental data. Differences observed in the behavior of the
full-width-at-half-maximum of the GDR for Sn and Pb are
attributed to the fact that shell corrections in Pb are stronger than
in Sn, and favor the spherical shape at low temperatures. The effects
shell corrections have on both the free energy and the moments of inertia are
discussed in detail. At high temperature, the FWHM in Sn exhibits
effects due to the evaporation width of the compound nucleus, while these
effects are predicted for Pb.Comment: 28 pages in RevTeX plus eight postscript figures. Submitted to Nucl.
Phys.
Compilation of Giant Electric Dipole Resonances Built on Excited States
Giant Electric Dipole Resonance (GDR) parameters for gamma decay to excited
states with finite spin and temperature are compiled. Over 100 original works
have been reviewed and from some 70 of which more than 300 parameter sets of
hot GDR parameters for different isotopes, excitation energies, and spin
regions have been extracted. All parameter sets have been brought onto a common
footing by calculating the equivalent Lorentzian parameters. The current
compilation is complementary to an earlier compilation by Samuel S. Dietrich
and Barry L. Berman (At. Data Nucl. Data Tables 38(1988)199-338) on
ground-state photo-neutron and photo-absorption cross sections and their
Lorentzian parameters. A comparison of the two may help shed light on the
evolution of GDR parameters with temperature and spin. The present compilation
is current as of January 2006.Comment: 31 pages including 1 tabl
Coulomb Effects on Particle Spectra in Relativistic Nuclear Collisions
Coulomb effects on and spectra in relativistic nuclear collisions are investigated. At collision energies around 1 GeV the ratio of at ultrarelativistic energies. We describe the ratios at SIS, AGS and SPS energies with simple analytic models as well as more elaborate numerical models incorporating the expansion dynamics. The Coulomb effect depends on the properties of the source after the violent collision phase and provides information on source sizes, freeze-out times, and expansion velocities. Comparison with results from HBT analyses are made. Predictions for and at RHIC and LHC energies are given
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