698 research outputs found
Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions
We review the most important experimental results from the first three years
of nucleus-nucleus collision studies at RHIC, with emphasis on results from the
STAR experiment, and we assess their interpretation and comparison to theory.
The theory-experiment comparison suggests that central Au+Au collisions at RHIC
produce dense, rapidly thermalizing matter characterized by: (1) initial energy
densities above the critical values predicted by lattice QCD for establishment
of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by
constituent interactions of very short mean free path, established most
probably at a stage preceding hadron formation; and (3) opacity to jets. Many
of the observations are consistent with models incorporating QGP formation in
the early collision stages, and have not found ready explanation in a hadronic
framework. However, the measurements themselves do not yet establish
unequivocal evidence for a transition to this new form of matter. The
theoretical treatment of the collision evolution, despite impressive successes,
invokes a suite of distinct models, degrees of freedom and assumptions of as
yet unknown quantitative consequence. We pose a set of important open
questions, and suggest additional measurements, at least some of which should
be addressed in order to establish a compelling basis to conclude definitively
that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.
Race-Specific Patterns of Treatment Intensification Among Hypertensive Patients Using Home Blood Pressure Monitoring: Analysis Using Defined Daily Doses in the Heart Healthy Lenoir Study
Background: Racial disparities in blood pressure (BP) control persist, but whether differences by race in antihypertensive medication intensification (AMI) contribute is unknown. Objective: To compare AMI by race for patients with elevated home BP readings. Methods: This prospective cohort study followed adult patients from 6 rural primary care practices who used home BP monitoring (HBPM) and recorded/reported values. For providers, AMI was encouraged when mean HBPM systolic blood pressure (SBP) values were ⩾135 mm Hg; patients received phone-based coaching on HBPM technique and sharing HBPM findings. AMI was assessed between baseline and 12 months using defined daily dose (DDD) and summed to create a total antihypertensive DDD value. Results: A total of 217 patients (mean age = 61.4 ± 10.2 years; 66% female; 57% black) provided usable HBPM data. Among 90 (41%) intensification-eligible hypertensive patients (ie, mean HBPM SBP values for 6-months ⩾135 mm Hg), mean total antihypertensive DDD was increased in 61% at 12 months. Blacks had significantly higher mean DDD at baseline and 12 months, but intensification (+0.72 vs +0.65; P = 0.83) was similar by race. However, intensification was greater in males than females (+1.1 vs +0.39; P = 0.031). Reduction in mean SBP following intensification was greater in white versus black patients (−8.2 vs −3.9 mm Hg; P = 0.14). Conclusion/Relevance: Treatment intensification in HBPM users was similar by race, differed significantly by gender, and may produce a greater response in white patients. Differential AMI in HBPM users does not appear to contribute to persistent racial disparities in BP control
Relative Abundances of Cosmic Ray Nuclei B-C-N-O in the Energy Region from 10 GeV/n to 300 GeV/n. Results from the Science Flight of the ATIC
The ATIC balloon-borne experiment measures the energy spectra of elements from H to Fe in primary cosmic rays from about 100 GeV to 100 TeV. ATIC is comprised of a fully active bismuth germanate calorimeter, a carbon target with embedded scintillator hodoscopes, and a silicon matrix that is used as a main charge detector. The silicon matrix produces good charge resolution for the protons and helium but only a partial resolution for heavier nuclei. In the present paper a charge resolution of ATIC device was essentially improved and backgrounds were reduced in the region from Be to Si by means of the upper layer of the scintillator hodoscope that was used as an additional charge detector together with the silicon matrix. The flux ratios of nuclei B/C, O/C, N/C in the energy region from about 10 GeV/nucleon to 300 GeV/nucleon that were obtained from new high-resolution and high-quality charge spectra of nuclei are presented. The results are compared with existing theoretical predictions
Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV
We report the STAR measurement of Phi meson production in Au+Au and p+p
collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi
spectra and yields are obtained at mid-rapidity for five centrality bins in
Au+Au collisions and for non-singly-diffractive p+p collisions. It is found
that the Phi transverse momentum distributions from Au+Au collisions are better
fitted with a single-exponential while the p+p spectrum is better described by
a double-exponential distribution. The measured nuclear modification factors
indicate that Phi production in central Au+Au collisions is suppressed relative
to peripheral collisions when scaled by the number of binary collisions. The
systematics of versus centrality and the constant Phi/K- ratio versus beam
species, centrality, and collision energy rule out kaon coalescence as the
dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let
Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at GeV
We present first measurements of the evolution of the differential transverse
momentum correlation function, {\it C}, with collision centrality in Au+Au
interactions at GeV. {\it C} exhibits a strong dependence
on collision centrality that is qualitatively similar to that of number
correlations previously reported. We use the observed longitudinal broadening
of the near-side peak of {\it C} with increasing centrality to estimate the
ratio of the shear viscosity to entropy density, , of the matter formed
in central Au+Au interactions. We obtain an upper limit estimate of
that suggests that the produced medium has a small viscosity per unit entropy.Comment: 7 pages, 4 figures, STAR paper published in Phys. Lett.
Energy and system size dependence of \phi meson production in Cu+Cu and Au+Au collisions
We study the beam-energy and system-size dependence of \phi meson production
(using the hadronic decay mode \phi -- K+K-) by comparing the new results from
Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4
and 200 GeV measured in the STAR experiment at RHIC. Data presented are from
mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the
transverse momentum distributions for \phi mesons are observed to be similar in
yield and shape for Cu+Cu and Au+Au colliding systems with similar average
numbers of participating nucleons. The \phi meson yields in nucleus-nucleus
collisions, normalised by the average number of participating nucleons, are
found to be enhanced relative to those from p+p collisions with a different
trend compared to strange baryons. The enhancement for \phi mesons is observed
to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations
for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision
energies, the source of enhancement of strange hadrons is related to the
formation of a dense partonic medium in high energy nucleus-nucleus collisions
and cannot be alone due to canonical suppression of their production in smaller
systems.Comment: 20 pages and 5 figure
Energy Spectra of Abundant Nuclei of Primary Cosmic Rays from the Data of ATIC-2 Experiment: Final Results
The final results of processing the data from the balloon-born experiment
ATIC-2 (Antarctica, 2002-2003) for the energy spectra of protons and He, C, O,
Ne, Mg, Si, and Fe nuclei, the spectrum of all particles, and the mean
logarithm of atomic weight of primary cosmic rays as a function of energy are
presented. The final results are based on improvement of the methods used
earlier, in particular, considerably increased resolution of the charge
spectrum. The preliminary conclusions on the significant difference in the
spectra of protons and helium nuclei (the proton spectrum is steeper) and the
non-power character of the spectra of protons and heavier nuclei (flattening of
carbon spectrum at energies above 10 TeV) are confirmed. A complex structure of
the energy dependence of the mean logarithm of atomic weight is found.Comment: 4 pages, a paper for 30th Russian Cosmic Ray Conference (2008, St.
Petersburg
Longitudinal scaling property of the charge balance function in Au + Au collisions at 200 GeV
We present measurements of the charge balance function, from the charged
particles, for diverse pseudorapidity and transverse momentum ranges in Au + Au
collisions at 200 GeV using the STAR detector at RHIC. We observe that the
balance function is boost-invariant within the pseudorapidity coverage [-1.3,
1.3]. The balance function properly scaled by the width of the observed
pseudorapidity window does not depend on the position or size of the
pseudorapidity window. This scaling property also holds for particles in
different transverse momentum ranges. In addition, we find that the width of
the balance function decreases monotonically with increasing transverse
momentum for all centrality classes.Comment: 6 pages, 3 figure
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