10,020 research outputs found
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
Equation of State and Collective Dynamics
This talk summarizes the present status of a program to quantitatively relate
data from the Relativistic Heavy Ion Collider (RHIC) on collective expansion
flow to the Equation of State (EOS) of hot and dense strongly interacting
matter, including the quark-gluon plasma and the quark-hadron phase transition.
The limits reached with the present state of the art and the next steps
required to make further progress will both be discussed.Comment: 8 pages, 6 two-part figures. Invited talk given at the 5th
International Conference on the Physics and Astrophysics of Quark-Gluon
Plasma (ICPAQGP 2005), Kolkata (India), Feb 8-12, 2005. Proceedings to be
published in Journal of Physics: Conference Series (Jan-E Alam et al., eds.
Optimal entanglement criterion for mixed quantum states
We develop a strong and computationally simple entanglement criterion. The
criterion is based on an elementary positive map Phi which operates on state
spaces with even dimension N >= 4. It is shown that Phi detects many entangled
states with positive partial transposition (PPT) and that it leads to a class
of optimal entanglement witnesses. This implies that there are no other
witnesses which can detect more entangled PPT states. The map Phi yields a
systematic method for the explicit construction of high-dimensional manifolds
of bound entangled states.Comment: 4 pages, no figures, replaced by published version (minor changes),
Journal-reference adde
Formation Time of QGP from Thermal Photon Elliptic Flow
We show that the transverse momentum dependent elliptic flow of
thermal photons is quite sensitive to the initial formation time () of
Quark Gluon Plasma (QGP) for semi-central collision of gold nuclei at RHIC
\cite{tau}. A smaller value of the formation time or a larger initial
temperature leads to a significant increase in the thermal photon radiation
from QGP phase, which has a smaller . The elliptic flow of thermal photon
is dominated by the contribution from the quark matter at intermediate and high
range and as a result sum decreases with smaller for GeV. On the other hand we find that the elliptic flow parameter for
hadrons depends only marginally on the value of .Comment: 4 pages, 3 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee, v2: minor
correction
Elliptic flow of thermal dileptons in relativistic nuclear collisions
We calculate the transverse momentum and invariant mass dependence of
elliptic flow of thermal dileptons for Au+Au collisions at the Relativistic
Heavy Ion Collider. The system is described using hydrodynamics, with the
assumption of formation of a thermalized quark-gluon plasma at some early time,
followed by cooling through expansion, hadronization and decoupling. Dileptons
are emitted throughout the expansion history: by annihilation of quarks and
anti-quarks inthe early quark-gluon plasma stage and through a set of hadronic
reactions during the late hadronic stage. The resulting differential elliptic
flow exhibits a rich structure, with different dilepton mass windows providing
access to different stages of the expansion history. Elliptic flow measurements
for dileptons,combined with those of hadrons and direct photons, are a powerful
tool for mapping the time-evolution of heavy-ion collisions.Comment: Latex 8 pages including a total of 13 postscript figures. Added 2
figures, additional references, and expanded discussions. Figures modified
for better viewing. To appear in Phys. Rev.
Elliptic flow of thermal photons in relativistic nuclear collisions
We predict the transverse momentum (pT) dependence of elliptic flow of
thermal photons for Au+Au collisions at the Relativistic Heavy Ion Collider. We
model the system hydrodynamically, assuming formation of a thermalized
quark-gluon plasma at some early time, followed by cooling through expansion,
hadronization and decoupling. Photons are emitted throughout the expansion
history. Contrary to hadron elliptic flow, which hydrodynamics predicts to
increase monotonically with pT, the elliptic flow of thermal photons is
predicted to first rise and then fall again as pT increases. Photon elliptic
flow at high pT is shown to reflect the quark momentum anisotropy at early
times when it is small, whereas at low pT it is controlled by the much larger
pion momentum anisotropy during the late hadronic emission stage. An
interesting structure is predicted at intermediate pT ~ 0.4 GeV/c where photon
elliptic flow reflects the momenta and the (compared to pions) reduced v2 of
heavy vector mesons in the late hadronic phase.Comment: 4 pages, 4 figures. Amended Fig. 3 and corresponding discussion, with
complete explanation of the low-pT structure of photon elliptic flow around
pT=400 MeV/
Electron Refrigeration in the Tunneling Approach
The qualities of electron refrigeration by means of tunnel junctions between
superconducting and normal--metal electrodes are studied theoretically. A
suitable approximation of the basic expression for the heat current across
those tunnel junctions allows the investigation of several features of the
device such as its optimal bias voltage, its maximal heat current, its optimal
working point, and the maximally gained temperature reduction. Fortunately, the
obtained results can be compared with those of a recent experiment.Comment: 4 pages, 4 Postscript figures, uses eps
- …