782 research outputs found
Determination of the reaction plane in ultrarelativistic nuclear collisions
In the particles produced in a nuclear collision undergo collective flow, the
reaction plane can in principle be determined through a global event analysis.
We show here that collective flow can be identified by evaluating the reaction
plane independently in two separate rapidity intervals, and studying the
correlation between the two results. We give an analytical expression for the
correlation function between the two planes as a function of their relative
angle. We also discuss how this correlation function is related to the
anisotropy of the transverse momentum distribution. Email contact:
[email protected]: Saclay-T93/026 Email: [email protected]
Azimuthal Correlations in the Target Fragmentation Region of High Energy Nuclear Collisions
Results on the target mass dependence of proton and pion pseudorapidity
distributions and of their azimuthal correlations in the target rapidity range
are presented. The data have been taken with the
Plastic-Ball detector set-up for 4.9 GeV p + Au collisions at the Berkeley
BEVALAC and for 200 GeV/ p-, O-, and S-induced reactions on
different nuclei at the CERN-SPS. The yield of protons at backward rapidities
is found to be proportional to the target mass. Although protons show a typical
``back-to-back'' correlations, a ``side-by-side'' correlation is observed for
positive pions, which increases both with target mass and with impact parameter
of a collision. The data can consistently be described by assuming strong
rescattering phenomena including pion absorption effects in the entire excited
target nucleus.Comment: 7 pages, figures included, complete postscript available at
ftp://qgp.uni-muenster.de/pub/paper/azi-correlations.ps submitted to Phys.
Lett.
The Origin of Transverse Flow at the SPS
We study the transverse expansion in central Pb+Pb collisions at the CERN
SPS. Strong collective motion of hadrons can be created. This flow is mainly
due to meson baryon rescattering. It allows to study the angular distribution
of intermediate mass meson baryon interactions.Comment: submitted to Phys. Lett.
Precision Spectroscopy at Heavy Ion Ring Accelerator SIS300
Unique spectroscopic possibilities open up if a laser beam interacts with
relativistic lithium-like ions stored in the heavy ion ring accelerator SIS300
at the future Facility for Antiproton and Ion Research FAIR in Darmstadt,
Germany. At a relativistic factor gamma = 36 the 2P 1/2 level can be excited
from the 2S 1/2 ground state for any element with frequency doubled dye-lasers
in collinear geometry. Precise transition energy measurements can be performed
if the fluorescence photons, boosted in forward direction into the X-ray
region, are energetically analyzed with a single crystal monochromator. The
hyperfine structure can be investigated at the 2P 1/2 - 2S 1/2 transition for
all elements and at the 2P 3/2 - 2S 1/2 transition for elements with Z < 50.
Isotope shifts and nuclear moments can be measured with unprecedented
precision, in principle even for only a few stored radioactive species with
known nuclear spin. A superior relative line width in the order of 5E-7 may be
feasible after laser cooling, and even polarized external beams may be prepared
by optical pumping
Heavy Ion Physics at RHIC
The status of the physics of heavy ion collisions is reviewed based on
measurements over the past 6 years from the Relativistic Heavy Ion Collider
(RHIC) at Brookhaven National Laboratory. The dense nuclear matter produced in
Au+Au collisions with nucleon-nucleon c.m. energy GeV at
RHIC corresponds roughly to the density and temperature of the universe a few
microseconds after the `big-bang' and has been described as "a perfect liquid"
of quarks and gluons, rather than the gas of free quarks and gluons, ``the
quark-gluon plasma" as originally envisaged. The measurements and arguments
leading to this description will be presented.Comment: 31 pages, 23 figures, Proceedings of Symposium "50+ Years of High
Energy Physics at UB", University at Buffalo, NY, October 20-21,200
In situ Measurements of pH, CA2+, and Dic Dynamics within the Extrapallial Fluid of the Ocean Quahog Arctica islandica
This study investigated to what extent the extrapallial fluid (EPF) of the marine bivalve Arctica islandica (Linneaus, 1767) is involved in shell formation. With in situ pH microscopy, pH gradients were identified between inner shell surface and outer mantle epithelium (OME). pH at the OME varied rapidly between neutral and values above 9, suggesting active H+ pumping. Microsensor measurements showed also remarkable short-term dynamics in pH and Ca2+ concentrations, again suggesting active ion pumping. Further focus was on pH, Ca2+, and dissolved inorganic carbon dynamics within the EPF to determine whether calcium carbonate precipitation is possible within the EPF. The data show that the bulk of the inner EPF rarely reaches calcium carbonate saturation and, thus, cannot be the site of shell formation. At the OME surface, however, pH levels of up to 9.5 were observed, corresponding to a 30-fold carbonate supersaturation. Thus, ion pumping by the OME can drive calcification when the OME is just a few mm distant from the inner shell surface, as it is the case in the outer E
Event Anisotropy in High Energy Nucleus-Nucleus Collisions
The predictions of event anisotropy parameters from transport model RQMD are
compared with the recent experimental measurements for 158 GeV Pb+Pb
collisions. Using the same model, we study the time evolution of event
anisotropy at 2 GeV and 158 GeV for several colliding systems. For the
first time, both momentum and configuration space information are studied using
the Fourier analysis of the azimuthal angular distribution. We find that, in
the model, the initial geometry of the collision plays a dominant role in
determining the anisotropy parameters.Comment: 18 pages, 7 figures, 2 table
Shock waves in strongly coupled plasmas
Shock waves are supersonic disturbances propagating in a fluid and giving
rise to dissipation and drag. Weak shocks, i.e., those of small amplitude, can
be well described within the hydrodynamic approximation. On the other hand,
strong shocks are discontinuous within hydrodynamics and therefore probe the
microscopics of the theory. In this paper we consider the case of the strongly
coupled N=4 plasma whose microscopic description, applicable for scales smaller
than the inverse temperature, is given in terms of gravity in an asymptotically
space. In the gravity approximation, weak and strong shocks should be
described by smooth metrics with no discontinuities. For weak shocks we find
the dual metric in a derivative expansion and for strong shocks we use
linearized gravity to find the exponential tail that determines the width of
the shock. In particular we find that, when the velocity of the fluid relative
to the shock approaches the speed of light the penetration depth
scales as . We compare the results with second
order hydrodynamics and the Israel-Stewart approximation. Although they all
agree in the hydrodynamic regime of weak shocks, we show that there is not even
qualitative agreement for strong shocks. For the gravity side, the existence of
shock waves implies that there are disturbances of constant shape propagating
on the horizon of the dual black holes.Comment: 47 pages, 8 figures; v2:typos corrected, references adde
Two-particle interferometry for non-central heavy-ion collisions
In non-central heavy ion collisions, identical two particle
Hanbury-Brown/Twiss (HBT) correlations C(K,q) depend on the azimuthal direction
of the pair momentum K. We investigate the consequences for a harmonic analysis
of the corresponding HBT radius parameters. Our discussion includes both, a
model- independent analysis of these parameters in the Gaussian approximation,
and the study of a class of hydrodynamical models which mimic essential
geometrical and dynamical properties of peripheral heavy ion collisions. Also,
we discuss the additional geometrical and dynamical information contained in
the harmonic coefficients of these HBT radius parameters. The leading
contribution of their first and second harmonics are found to satisfy simple
constraints. This allows for a minimal, azimuthally sensitive parametrization
of all first and second harmonic coefficients in terms of only two additional
fit parameters. We determine to what extent these parameters can be extracted
from experimental data despite finite multiplicity fluctuations and the
resulting uncertainty in the reconstruction of the reaction plane.Comment: 14 pages, RevTeX, 7 eps-figures include
Viral Escape in the Central Nervous System with Multidrug-Resistant Human Immunodeficiency Virus-1
In this study, we report the case of a patient infected with human immunodeficiency virus (HIV)-1 who developed ataxia and neurocognitive impairment due to viral escape within the central nervous system (CNS) with a multidrug-resistant HIV-1 despite long-term viral suppression in plasma. Antiretroviral therapy optimization with drugs with high CNS penetration led to viral suppression in the CSF, regression of ataxia, and improvement of neurocognitive symptom
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