8,824 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
Dust interferometers in plasmas
An interferometric imaging technique has been proposed to instantly measure
the diameter of individual spherical dust particles suspended in a gas
discharge plasma. The technique is based on the defocused image analysis of
both spherical particles and their binary agglomerates. Above a critical
diameter, the defocused images of spherical particles contain stationary
interference fringe patterns and the fringe number increases with particle
diameters. Below this critical diameter, the particle size has been measured
using the rotational interference fringe patterns which appear only on the
defocused images of binary agglomerates. In this case, a lower cut-off limit of
particle diameter has been predicted, below which no such rotational fringe
patterns are observed for the binary agglomerates. The method can be useful as
a diagnostics for complex plasma experiments on earth as well as under
microgravity condition
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
Confinement and crowding control the morphology and dynamics of a model bacterial chromosome
Motivated by recent experiments probing shape, size and dynamics of bacterial
chromosomes in growing cells, we consider a polymer model consisting of a
circular backbone to which side-loops are attached, confined to a cylindrical
cell. Such a model chromosome spontaneously adopts a helical shape, which is
further compacted by molecular crowders to occupy a nucleoid-like subvolume of
the cell. With increasing cell length, the longitudinal size of the chromosome
increases in a non-linear fashion to finally saturate, its morphology gradually
opening up while displaying a changing number of helical turns. For shorter
cells, the chromosome extension varies non-monotonically with cell size, which
we show is associated with a radial to longitudinal spatial reordering of the
crowders. Confinement and crowders constrain chain dynamics leading to
anomalous diffusion. While the scaling exponent for the mean squared
displacement of center of mass grows and saturates with cell length, that of
individual loci displays broad distribution with a sharp maximum.Comment: 12 pages, 12 figure
Quasi-two-dimensional complex plasma containing spherical particles and their binary agglomerates
A new type of quasi-two-dimensional complex plasma system was observed which
consisted of monodisperse microspheres and their binary agglomerations
(dimers). The particles and their dimers levitated in a plasma sheath at
slightly different heights and formed two distinct sublayers. The sys- tem did
not crystallize and may be characterized as disordered solid. The dimers were
identified based on their characteristic appearance in defocused images, i.e.,
rotating interference fringe pat- terns. The in-plane and inter-plane particle
separations exhibit nonmonotonic dependence on the discharge pressure which
agrees well with theoretical predictions
Stochastic thermodynamics of macrospins with fluctuating amplitude and direction
We consider stochastic energy balance and entropy production (EP) in a
generalized Langevin dynamics of macrospins, allowing for both amplitude and
direction fluctuations, under external magnetic field. EP is calculated using
Fokker-Planck equation, distinguishing between reversible and irreversible
parts of probability currents. The system entropy increases due to irreversible
non-equilibrium processes, and reduces as heat dissipates to surrounding
environment. Using path probability distributions of time-forward trajectories
and conjugate trajectories under time reversal, we obtain fluctuation theorems
(FT) for total stochastic EP. We show that the choice of conjugate trajectories
is crucial in obtaining entropy like quantities that obey FTs.Comment: 7 pages, no figure; version accepted for publication in Phys. Rev.
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
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