546 research outputs found
Dissipation and fragmentation of low-Q^2 scattered partons in Au-Au collisions at RHIC
Two-particle correlations and event-wise fluctuations in transverse momentum
p_t are reported for Au-Au collisions at sqrt{s_{NN}} = 62 and 200 GeV on
pseudorapidity (eta) and azimuth (phi). Distributions of all pairs of particles
(no leading trigger particle) reveal jet-like correlations, or peaks at
pair-wise opening angles of order 1 radian or less. The width of this same-side
correlation peak increases dramatically on pseudorapidity and decreases on
azimuth for increasing collision centrality. Evolution of the same-side peak
with centrality suggests dissipation of low-Q^2 partons via strong coupling to
an expanding bulk medium. p_t correlations, which provide access to temperature
and/or velocity distributions in the colliding system, are also presented.Comment: 4 pages, 2 figures, conference poster write-u
Angular Correlations in STAR
The related studies of two-particle correlations and event-by-event fluctuations have played important roles in the search for new physics through the experimental study of relativistic heavy ion collisions. We present a general method of determining minimum-bias two-particle correlations and show the relationship between these correlations and event-by-event fluctuations. Data from the STAR experiment at RHIC for Au-Au collisions at = 62 and 200 GeV will be presented that show the energy and centrality dependences of angular correlations. This analysis provides a unique method for studying the interaction of semi-hard scattered partons with the dense medium produced at RHIC as well as properties of the bulk medium itself, and will shed new light on the sources of non-statistical fluctuations
Azimuth Quadrupole Systematics in Au-Au Collisions
We have measured -dependent two-particle number correlations on azimuth
and pseudorapidity for eleven centralities of and 200~GeV
Au-Au collisions at STAR. 2D fits to these angular correlations isolate the
azimuth quadrupole amplitude, denoted , from
localized same-side correlations. Event-plane measurements within
the STAR TPC acceptance can be expressed as a sum of the azimuth quadrupole and
the quadrupole component of the same-side peak. can be
transformed to reveal quadrupole spectra which are approximately
described by a fixed transverse boost and universal L\'evy form nearly
independent of centrality. A parametrization of can be
factored into centrality and -dependent pieces with a simple
dependence above 0.75 GeV/c. Results from STAR are compared to published data
and model predictions.Comment: Conference proceedings for Hot Quarks 201
Fluctuation and flow probes of early-time correlations in relativistic heavy ion collisions
Fluctuation and correlation observables are often measured using
multi-particle correlation methods and therefore mutually probe the origins of
genuine correlations present in multi-particle distribution functions. We
investigate the common influence of correlations arising from the spatially
inhomogeneous initial state on multiplicity and momentum fluctuations as well
as flow fluctuations. Although these observables reflect different aspects of
the initial state, taken together, they can constrain a correlation scale set
at the earliest moments of the collision. We calculate both the correlation
scale in an initial stage Glasma flux tube picture and the modification to
these correlations from later stage hydrodynamic flow and find quantitative
agreement with experimental measurements over a range of collision systems and
energies.Comment: Proceedings of the 28th Winter Workshop on Nuclear Dynamics, Dorado
del Mar, Puerto Rico, April 7-14, 201
Applicability of Monte Carlo Glauber models to relativistic heavy ion collision data
The accuracy of Monte Carlo Glauber model descriptions of minimum-bias
multiplicity frequency distributions is evaluated using data from the
Relativistic Heavy Ion Collider (RHIC) within the context of a sensitive,
power-law representation introduced previously by Trainor and Prindle (TP).
Uncertainties in the Glauber model input and in the mid-rapidity multiplicity
frequency distribution data are reviewed and estimated using the TP centrality
methodology. The resulting errors in model-dependent geometrical quantities
used to characterize heavy ion collisions ({\em i.e.} impact parameter, number
of nucleon participants , number of binary interactions ,
and average number of binary collisions per incident participant nucleon )
are presented for minimum-bias Au-Au collisions at = 20, 62,
130 and 200 GeV and Cu-Cu collisions at = 62 and 200 GeV.
Considerable improvement in the accuracy of collision geometry quantities is
obtained compared to previous Monte Carlo Glauber model studies, confirming the
TP conclusions. The present analysis provides a comprehensive list of the
sources of uncertainty and the resulting errors in the above geometrical
collision quantities as functions of centrality. The capability of energy
deposition data from trigger detectors to enable further improvements in the
accuracy of collision geometry quantities is also discussed.Comment: 27 pages, 4 figures, 11 table
Viscosity and the Soft Ridge at RHIC
Correlation studies exhibit a ridge-like feature in rapidity and azimuthal
angle, with and without a jet trigger. We ask whether the feature in
untriggered correlations can be a consequence of transverse flow and viscous
diffusion.Comment: Proc. Quark Matter 2008, Jaipur, Indi
Understanding jet quenching and medium response with di-hadron correlation
A brief review of the dependence of the dihadron correlations from RHIC
is presented. We attempt to construct a consistent picture that can describe
the data as a whole, focusing on the following important aspects, 1) the
relation between jet fragmentation of survived jet and medium response to
quenched jets, 2) the possible origin of the medium response and its relation
to intermediate physics for single hadron production, 3) the connection
between the near-side ridge and away-side cone, 4) and their relations to low
energy results.Comment: 8 pages, 8 figures, presented at the 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 2008. Updated with the published versio
Quantifying Properties of the QCD Matter at RHIC
We will review recent results on quantitative description of global
properties of bulk partonic matter at RHIC. These results include strangeness
phase space factor of the partonic matter, azimuthal angular anisotropy ,
and transverse momentum distributions of effective partons at the
hadronization of bulk partonic matter. We present empirical constraints on
parton energy loss in the high region ( 5 GeV/c). A flat as a
function of at mid-rapidity implies a constant fraction of the parton
energy loss () and the fraction reaches 25% for neutral ,
charged hadrons and non-photonic electrons of heavy quark decays from central
Au+Au collisions at 200 GeV. Collision centrality dependence of
from Au+Au and Cu+Cu collisions indicates that the fraction is
approximately proportional to particle rapidity density divided by the
initial transverse overlapping area of the colliding nuclei. Implications on
dynamics of parton energy loss will be discussed.Comment: To Appear in SQM2008 Conference Proceeding
Novel Bose-Einstein Interference in the Passage of a Fast Particle in a Dense Medium
When an energetic particle collides coherently with many medium particles at
high energies, the Bose-Einstein symmetry with respect to the interchange of
the exchanged virtual bosons leads to a destructive interference of the Feynman
amplitudes in most regions of the phase space but a constructive interference
in some other regions of the phase space. As a consequence, the recoiling
medium particles have a tendency to come out collectively along the direction
of the incident fast particle, each carrying a substantial fraction of the
incident longitudinal momentum. Such an interference appearing as collective
recoils of scatterers along the incident particle direction may have been
observed in angular correlations of hadrons associated with a high-
trigger in high-energy AuAu collisions at RHIC.Comment: 10 pages, 2 figures, invited talk presented at the 35th Symposium on
Nuclear Physics, Cocoyoc, Mexico, January 3, 2012, to be published in IOP
Conference Serie
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