7,812 research outputs found
Analysis of one- and two-particle spectra at RHIC based on a hydrodynamical model
We calculate the one-particle hadronic spectra and correlation functions of
pions based on a hydrodynamical model. Parameters in the model are so chosen
that the one-particle spectra reproduce experimental results of
GeV Au+Au collisions at RHIC. Based on the numerical solution,
we discuss the space-time evolution of the fluid. Two-pion correlation
functions are also discussed. Our numerical solution suggests the formation of
the quark-gluon plasma with large volume and low net baryon density.Comment: LaTeX, 4pages, 4 figures. To appear in the proceedings of Fourth
International Conference on Physics and Astrophysics of Quark-Gluon Plasma
(ICPAQGP-2001), Nov 26-30, 2001, Jaipur, Indi
A Ray-Tracing Model of the Vela Pulsar
In the relativistic plasma surrounding a pulsar, a subluminal ordinary-mode
electromagnetic wave will propagate along a magnetic field line. After some
distance, it can break free of the field line and escape the magnetosphere to
reach an observer. We describe a simple model of pulsar radio emission based on
this scenario and find that applying this model to the case of the Vela pulsar
reproduces qualitative characteristics of the observed Vela pulse profile.Comment: 23 pages, 9 figures, accepted for publication in Ap
Search for the onset of baryon anomaly at RHIC-PHENIX
The baryon production mechanism at the intermediate (2 - 5 GeV/) at
RHIC is still not well understood. The beam energy scan data in Cu+Cu and Au+Au
systems at RHIC may provide us a further insight on the origin of the baryon
anomaly and its evolution as a function of . In 2005 RHIC
physics program, the PHENIX experiment accumulated the first intensive low beam
energy data in Cu+Cu collisions. We present the preliminary results of
identified charged hadron spectra in Cu+Cu at = 22.5 and 62.4
GeV using the PHENIX detector. The centrality and beam energy dependences of
(anti)proton to pion ratios and the nuclear modification factors for charged
pions and (anti)protons are presented.Comment: 5 pages, 9 figures, proceedings for Hot Quarks 2006 workshop,
Villasimius, Sardinia, Italy, May 15 - 20, 2006. Proceedings of the
conference will be published in The European Physical Journal
Interplay between soft and hard hadronic components for identified hadrons in relativistic heavy ion collisions
We investigate the transverse dynamics in Au+Au collisions at \sqrt{s_NN}=200
GeV by emphasis upon the interplay between soft and hard components through p_T
dependences of particle spectra, ratios of yields, suppression factors, and
elliptic flow for identified hadrons. From hydrodynamics combined with
traversing minijets which go through jet quenching in the hot medium, we
calculate interactions of hard jets with the soft hydrodynamic components. It
is shown by the explicit dynamical calculations that the hydrodynamic radial
flow and the jet quenching of hard jets are the keys to understand the
differences among the hadron spectra for pions, kaons, and protons. This leads
to the natural interpretation for N_p/N_\pi ~ 1, R_{AA} >~ 1 for protons, and
v_2^p > v_2^\pi recently observed in the intermediate transverse momentum
region at Relativistic Heavy Ion Collider (RHIC).Comment: 11 pages, 9 figures; some references added; title changed, some data
points included in figure
The use of prognostic scores for causal inference with general treatment regimes
In nonrandomised studies, inferring causal effects requires appropriate methods for addressing confounding bias. Although it is common to adopt propensity score analysis to this purpose, prognostic score analysis has recently been proposed as an alternative strategy. While both approaches were originally introduced to estimate causal effects for binary interventions, the theory of propensity score has since been extended to the case of general treatment regimes. Indeed, many treatments are not assigned in a binary fashion and require a certain extent of dosing. Hence, researchers may often be interested in estimating treatment effects across multiple exposures. To the best of our knowledge, the prognostic score analysis has not been yet generalised to this case. In this article, we describe the theory of prognostic scores for causal inference with general treatment regimes. Our methods can be applied to compare multiple treatments using nonrandomised data, a topic of great relevance in contemporary evaluations of clinical interventions. We propose estimators for the average treatment effects in different populations of interest, the validity of which is assessed through a series of simulations. Finally, we present an illustrative case in which we estimate the effect of the delay to Aspirin administration on a composite outcome of death or dependence at 6Â months in stroke patients
Hydrodynamical analysis of hadronic spectra in the 130 GeV/nucleon Au+Au collisions
We study one-particle spectra and a two-particle correlation function in the
130 GeV/nucleon Au+Au collisions at RHIC by making use of a hydrodynamical
model. We calculate the one-particle hadronic spectra and present the first
analysis of Bose-Einstein correlation functions based on the numerical solution
of the hydrodynamical equations which takes both longitudinal and transverse
expansion into account appropriately. The hydrodynamical model provides
excellent agreement with the experimental data in the pseudorapidity and the
transverse momentum spectra of charged hadrons, the rapidity dependence of
anti-proton to proton ratio, and almost consistent result for the pion
Bose-Einstein correlation functions. Our numerical solution with simple
freeze-out picture suggests the formation of the quark-gluon plasma with large
volume and low net-baryon density.Comment: 7 pages, 8 figures, REVTeX4. Numerical results and figures are
correcte
Unitary Theory of Evaporating 2D Black Holes
We study a manifestly unitary formulation of 2d dilaton quantum gravity based
on the reduced phase space quantization. The spacetime metric can be expanded
in a formal power series of the matter energy-momentum tensor operator. This
expansion can be used for calculating the quantum corrections to the classical
black hole metric by evaluating the expectation value of the metric operator in
an appropriate class of the physical states. When the normal ordering in the
metric operator is chosen to be with respect to Kruskal vacuum, the lowest
order semiclassical metric is exactly the one-loop effective action metric
discovered by Bose, Parker and Peleg. The corresponding semiclassical geometry
describes an evaporating black hole which ends up as a remnant. The calculation
of higher order corrections and implications for the black hole fate are
discussed.Comment: LaTex fil
Comparison of space-time evolutions of hot/dense matter in =17 and 130 GeV relativistic heavy ion collisions based on a hydrodynamical model
Based on a hydrodynamical model, we compare 130 GeV/ Au+Au collisions at
RHIC and 17 GeV/ Pb+Pb collisions at SPS. The model well reproduces the
single-particle distributions of both RHIC and SPS.
The numerical solution indicates that huge amount of collision energy in RHIC
is mainly used to produce a large extent of hot fluid rather than to make a
high temperature matter; longitudinal extent of the hot fluid in RHIC is much
larger than that of SPS and initial energy density of the fluid is only 5%
higher than the one in SPS. The solution well describes the HBT radii at SPS
energy but shows some deviations from the ones at RHIC.Comment: 28 pages, 21 figures, REVTeX4, one figure is added and some figures
are replace
Theory and Phenomenology of Heavy Flavor at RHIC
We review the problem of heavy-quark diffusion in the Quark-Gluon Plasma and
its ramifications for heavy-quark spectra in heavy-ion collisions at RHIC. In
particular, we attempt to reconcile underlying mechanisms of several seemingly
different approaches that have been put forward to explain the large
suppression and elliptic flow of non-photonic electron spectra. We also
emphasize the importance of a quantitative description of the bulk medium
evolution to extract reliable values for the heavy-quark diffusion coefficient.Comment: 8 pages latex, including 10 eps figures; plenary talk at SQM08,
Beijing (China), Oct. 06-10, 200
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