2,488 research outputs found
Estimations of at RHIC from a QGP Model with Diquarks
Assuming that axial-vector and scalar diquarks exist in the Quark-Gluon
Plasma near the critical temporature , baryons can be produced from
quark-diquark interactions. In RHIC conditions ( and
), the ratio may be larger than 1, based on
the concept that QGP with diquarks would exist. This unusual result might be a
helpful evidence for QGP existing in RHIC.Comment: 6 pages, 1 figure. accepted by J.Phys.
Hadron production in heavy ion collisions: Fragmentation and recombination from a dense parton phase
We discuss hadron production in heavy ion collisions at RHIC. We argue that
hadrons at transverse momenta P_T < 5 GeV are formed by recombination of
partons from the dense parton phase created in central collisions at RHIC. We
provide a theoretical description of the recombination process for P_T > 2 GeV.
Below P_T = 2 GeV our results smoothly match a purely statistical description.
At high transverse momentum hadron production is well described in the language
of perturbative QCD by the fragmentation of partons. We give numerical results
for a variety of hadron spectra, ratios and nuclear suppression factors. We
also discuss the anisotropic flow v_2 and give results based on a flow in the
parton phase. Our results are consistent with the existence of a parton phase
at RHIC hadronizing at a temperature of 175 MeV and a radial flow velocity of
0.55c.Comment: 25 pages LaTeX, 18 figures; v2: some references updated; v3: some
typos fixe
The STAR Silicon Strip Detector (SSD)
The STAR Silicon Strip Detector (SSD) completes the three layers of the
Silicon Vertex Tracker (SVT) to make an inner tracking system located inside
the Time Projection Chamber (TPC). This additional fourth layer provides two
dimensional hit position and energy loss measurements for charged particles,
improving the extrapolation of TPC tracks through SVT hits. To match the high
multiplicity of central Au+Au collisions at RHIC the double sided silicon strip
technology was chosen which makes the SSD a half million channels detector.
Dedicated electronics have been designed for both readout and control. Also a
novel technique of bonding, the Tape Automated Bonding (TAB), was used to
fullfill the large number of bounds to be done. All aspects of the SSD are
shortly described here and test performances of produced detection modules as
well as simulated results on hit reconstruction are given.Comment: 11 pages, 8 figures, 1 tabl
Hydrodynamic emission of strange and non-strange particles at RHIC and LHC
The hydrodynamic model is used to describe the single-particle spectra and
elliptic flow of hadrons at RHIC and to predict the emission angle dependence
of HBT correlations at RHIC and LHC energies.Comment: 6 pages LaTeX, 3 postscript figures. Proceedings for the conference
"Strange Quark Matter 2003", Atlantic Beach, NC, March 12-17, 2003, to appear
in J. Phys.
Transverse energy production and charged-particle multiplicity at midrapidity in various systems from to 200 GeV
Measurements of midrapidity charged particle multiplicity distributions,
, and midrapidity transverse-energy distributions,
, are presented for a variety of collision systems and energies.
Included are distributions for AuAu collisions at ,
130, 62.4, 39, 27, 19.6, 14.5, and 7.7 GeV, CuCu collisions at
and 62.4 GeV, CuAu collisions at
GeV, UU collisions at GeV,
Au collisions at GeV, HeAu collisions at
GeV, and collisions at
GeV. Centrality-dependent distributions at midrapidity are presented in terms
of the number of nucleon participants, , and the number of
constituent quark participants, . For all collisions
down to GeV, it is observed that the midrapidity data
are better described by scaling with than scaling with . Also presented are estimates of the Bjorken energy density,
, and the ratio of to ,
the latter of which is seen to be constant as a function of centrality for all
systems.Comment: 706 authors, 32 pages, 20 figures, 34 tables, 2004, 2005, 2008, 2010,
2011, and 2012 data. v2 is version accepted for publication in Phys. Rev.
Medium modification of jet fragmentation in Au+Au collisions at sqrt(s_NN)=200 GeV measured in direct photon-hadron correlations
The jet fragmentation function is measured with direct photon-hadron
correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the
photon is an excellent approximation to the initial p_T of the jet and the
ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation
function. A statistical subtraction is used to extract the direct photon-hadron
yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_
AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates
modification of the jet fragmentation function. Suppression, most likely due to
energy loss in the medium, is seen at high z_T. The fragment yield at low z_T
is enhanced at large angles. Such a trend is expected from redistribution of
the lost energy into increased production of low-momentum particles.Comment: 562 authors, 70 insitutions, 8 pages, and 3 figures. Submitted to
Phys. Rev. Lett. v2 has minor changes to improve clarity. Plain text data
tables for the points plotted in figures for this and previous PHENIX
publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Measurements of elliptic and triangular flow in high-multiplicity HeAu collisions at GeV
We present the first measurement of elliptic () and triangular ()
flow in high-multiplicity HeAu collisions at
GeV. Two-particle correlations, where the particles have a large separation in
pseudorapidity, are compared in HeAu and in collisions and
indicate that collective effects dominate the second and third Fourier
components for the correlations observed in the HeAu system. The
collective behavior is quantified in terms of elliptic and triangular
anisotropy coefficients measured with respect to their corresponding
event planes. The values are comparable to those previously measured in
Au collisions at the same nucleon-nucleon center-of-mass energy.
Comparison with various theoretical predictions are made, including to models
where the hot spots created by the impact of the three He nucleons on the
Au nucleus expand hydrodynamically to generate the triangular flow. The
agreement of these models with data may indicate the formation of low-viscosity
quark-gluon plasma even in these small collision systems.Comment: 630 authors, 9 pages, 4 figures, 2 tables. v2 is the version accepted
for publication by Physical Review Letters. Plain text data tables for the
points plotted in figures for this and previous PHENIX publications are (or
will be) publicly available at http://www.phenix.bnl.gov/papers.htm
High-pT pi^zero Production with Respect to the Reaction Plane in Au + Au Collisions at sqrt(s_NN) = 200 GeV
Measurements of the azimuthal anisotropy of high-\pT neutral pion neutral
pion production in Au+Au collisions at sqrt(s_NN) = 200 GeV by the PHENIX
experiment are presented. The data included in this paper were collected during
the 2004 RHIC running period and represent approximately an order of magnitude
increase in the number of analyzed events relative to previously published
results. Azimuthal angle distributions of pi^0s detected in the PHENIX
electromagnetic calorimeters are measured relative to the reaction plane
determined event-by-event using the forward and backward beam-beam counters.
Amplitudes of the second Fourier component (v_2) of the angular distributions
are presented as a function of pi^0 transverse momentum p_T for different bins
in collision centrality. Measured reaction plane dependent pi^0 yields are used
to determine the azimuthal dependence of the pi^0 suppression as a function of
p_T, R_AA (Delta phi,p_T). A jet-quenching motivated geometric analysis is
presented that attempts to simultaneously describe the centrality dependence
and reaction plane angle dependence of the pi^0 suppression in terms of the
path lengths of hypothetical parent partons in the medium. This set of results
allows for a detailed examination of the influence of geometry in the collision
region, and of the interplay between collective flow and jet-quenching effects
along the azimuthal axis.Comment: 344 authors, 35 pages text, RevTeX-4, 24 figures, 8 tables. Submitted
to Physical Review
Transverse momentum and centrality dependence of dihadron correlations in Au+Au collisions at sqrt(s_NN)=200 GeV: Jet-quenching and the response of partonic matter
Azimuthal angle \Delta\phi correlations are presented for charged hadrons
from dijets for 0.4 < p_T < 10 GeV/c in Au+Au collisions at sqrt(s_NN) = 200
GeV. With increasing p_T, the away-side distribution evolves from a broad to a
concave shape, then to a convex shape. Comparisons to p+p data suggest that the
away-side can be divided into a partially suppressed "head" region centered at
Delta\phi ~ \pi, and an enhanced "shoulder" region centered at Delta\phi ~ \pi
+/- 1.1. The p_T spectrum for the "head" region softens toward central
collisions, consistent with the onset of jet quenching. The spectral slope for
the "shoulder" region is independent of centrality and trigger p_T, which
offers constraints on energy transport mechanisms and suggests that the
"shoulder" region contains the medium response to energetic jets.Comment: 420 authors from 58 institutions, 6 pages, 4 figures. Submitted to
Physical Review Letters. Plain text data tables for the points plotted in
figures for this and previous PHENIX publications are (or will be) publicly
available at http://www.phenix.bnl.gov/papers.htm
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