5,429 research outputs found
production in Au+Au/Cu+Cu collisions at =200 GeV and the threshold model
Using the QGP motivated threshold model, where all the 's are
suppressed above a threshold density, we have analyzed the preliminary PHENIX
data on the centrality dependence of nuclear modification factor for 's
in Cu+Cu and in Au+Au collisions, at RHIC energy, =200 GeV.
Centrality dependence of suppression in Au+Au collisions are well
explained in the model for threshold densities in ranges of 3.6-3.7 .
suppression in Cu+Cu collisions on the other hand are not explained in
the model.Comment: 6 pages, 5 figure
Conical flow due to partonic jets in central Au+Au collisions
In jet quenching, a hard QCD parton, before fragmenting into a jet of
hadrons, deposits a fraction of its energy in the medium, leading to suppressed
production of high- hadrons. The process can generate shock waves. We
study the distortion of Mach shock waves due to jet quenching in central Au+Au
collisions and its effect on particle production. Finite fluid velocity and
inhomogeneity of the medium can distort the Mach shock front significantly such
that the inside shock front disappear and the outside shock front is opened up.
We also show that the STAR data on azimuthal distribution of background
subtracted secondaries, associated with high trigger, are reasonably well
explained by the excess pions produced due to partonic energy loss.Comment: 4 pages, 4 figure
Transverse energy distributions and production in Pb+Pb collisions
We have analyzed the latest NA50 data on transverse energy distributions and
suppression in Pb+Pb collisions. The transverse energy distribution
was analysed in the geometric model of AA collisions. In the geometric model,
fluctuations in the number of NN collisions at fixed impact parameter are taken
into account. Analysis suggests that in Pb+Pb collisions, individual NN
collisions produces less , than in other AA collisions. The nucleons are
more transparent in Pb+Pb collisions. The transverse energy dependence of the
suppression was obtained following the model of Blaizot et al, where
charmonium suppression is assumed to be 100% effective above a threshold
density. With fluctuations in number of NN collisions taken into account, good
fit to the data is obtained, with a single parameter, the threshold density.Comment: Revised version with better E_T fit. 4 pages, 2 figure
Effects of jet quenching on the hydrodynamical evolution of quark-gluon plasma
We study the effects of jet quenching on the hydrodynamical evolution of the
quark-gluon plasma (QGP) fluid created in a heavy-ion collision. In jet
quenching, a hard QCD parton, before fragmenting into a jet of hadrons,
deposits a fraction of its energy in the medium, leading to suppressed
production of high-pT hadrons. Assuming that the deposited energy quickly
thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP
fluid. For partons moving at supersonic speed, v_p > c_s, and sufficiently
large energy loss, a shock wave forms leading to conical flow [1]. The PHENIX
Collaboration recently suggested that observed structures in the azimuthal
angle distribution [2] might be caused by conical flow. We show here that
conical flow produces different angular structures than predicted in [1] and
that, for phenomenologically acceptable values of parton energy loss, conical
flow effects are too weak to explain the structures seen by PHENIX [2].Comment: 4 pages, 3 figures. Last figure changed, now showing angular
distribution of pions instead of photons. Added comments on "lost jets" and
pT-dependence of angular correlation
Differentially Private Model Selection with Penalized and Constrained Likelihood
In statistical disclosure control, the goal of data analysis is twofold: The
released information must provide accurate and useful statistics about the
underlying population of interest, while minimizing the potential for an
individual record to be identified. In recent years, the notion of differential
privacy has received much attention in theoretical computer science, machine
learning, and statistics. It provides a rigorous and strong notion of
protection for individuals' sensitive information. A fundamental question is
how to incorporate differential privacy into traditional statistical inference
procedures. In this paper we study model selection in multivariate linear
regression under the constraint of differential privacy. We show that model
selection procedures based on penalized least squares or likelihood can be made
differentially private by a combination of regularization and randomization,
and propose two algorithms to do so. We show that our private procedures are
consistent under essentially the same conditions as the corresponding
non-private procedures. We also find that under differential privacy, the
procedure becomes more sensitive to the tuning parameters. We illustrate and
evaluate our method using simulation studies and two real data examples
Learning Arbitrary Statistical Mixtures of Discrete Distributions
We study the problem of learning from unlabeled samples very general
statistical mixture models on large finite sets. Specifically, the model to be
learned, , is a probability distribution over probability
distributions , where each such is a probability distribution over . When we sample from , we do not observe
directly, but only indirectly and in very noisy fashion, by sampling from
repeatedly, independently times from the distribution . The problem is
to infer to high accuracy in transportation (earthmover) distance.
We give the first efficient algorithms for learning this mixture model
without making any restricting assumptions on the structure of the distribution
. We bound the quality of the solution as a function of the size of
the samples and the number of samples used. Our model and results have
applications to a variety of unsupervised learning scenarios, including
learning topic models and collaborative filtering.Comment: 23 pages. Preliminary version in the Proceeding of the 47th ACM
Symposium on the Theory of Computing (STOC15
production in Au+Au collisions at RHIC and the nuclear absorption
It is shown that a QCD based nuclear absorption model, with few parameters
fixed to reproduce experimental yield in 200 GeV pp/pA and 450 GeV pA
collisions can explain the preliminary PHENIX data on the centrality dependence
of suppression in Cu+Cu collisions at RHIC energy, =200
GeV. However, the model does not give satisfactory description to the
preliminary PHENIX data on the centrality dependence of suppression in
Au+Au collisions. The analysis suggest that in Au+Au collisions, are
suppressed in a medium unlike the medium produced in SPS energy nuclear
collisions or in RHIC energy Cu+Cu collisions.Comment: Revised version, published in Phys. Rev. C 74(2006)044907. PHENIX
preliminary data on the centrality dependence of nuclear modification factor
for in Cu+Cu and in Au+Au are analysed. 6 pages, 5 figure
Di-jet hadron pair correlation in a hydrodynamical model with a quenching jet
In jet quenching, a hard QCD parton, before fragmenting into a jet of
hadrons, deposits a fraction of its energy in the medium, leading to suppressed
production of high- hadrons. Assuming that the deposited energy quickly
thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP
fluid. Hydrodynamic evolution and subsequent particle emission depend on the
jet trajectories. Azimuthal distribution of excess due to quenching
jet, averaged over all the trajectories, reasonably well reproduce the
di-hadron correlation as measured by the STAR and PHENIX collaboration in
central and in peripheral Au+Au collisions.Comment: 5 pages, 4 figures. Some minor corrections are made in the revised
manuscrip
Deconfinement and the Hagedorn Transition in String Theory
Superseded and extended in hep-th/0105110 and hep-th/0208112.Comment: Superseded and extended in hep-th/0105110 and hep-th/020811
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