7,355 research outputs found
Rapidity equilibration and longitudinal expansion at RHIC
The evolution of net-proton rapidity spectra with sqrt(s_NN) in heavy
relativistic systems is proposed as an indicator for local equilibration and
longitudinal expansion. In a Relativistic Diffusion Model, bell-shaped
distributions in central collisions at AGS energies and double-humped
nonequilibrium spectra at SPS show pronounced longitudinal collective expansion
when compared to the available data. The broad midrapidity valley recently
discovered at RHIC in central Au+Au collisions at sqrt(s_NN) = 200 GeV
indicates rapid local equilibration which is most likely due to deconfinement,
and fast longitudinal expansion of the locally equilibrated subsystem. A
prediction is made for Au+Au at sqrt(s_NN)= 62.4 GeV.Comment: 11 pages, 1 table, 2 figures; changes/additions in text, table, fig
Analysis of one- and two-particle spectra at RHIC based on a hydrodynamical model
We calculate the one-particle hadronic spectra and correlation functions of
pions based on a hydrodynamical model. Parameters in the model are so chosen
that the one-particle spectra reproduce experimental results of
GeV Au+Au collisions at RHIC. Based on the numerical solution,
we discuss the space-time evolution of the fluid. Two-pion correlation
functions are also discussed. Our numerical solution suggests the formation of
the quark-gluon plasma with large volume and low net baryon density.Comment: LaTeX, 4pages, 4 figures. To appear in the proceedings of Fourth
International Conference on Physics and Astrophysics of Quark-Gluon Plasma
(ICPAQGP-2001), Nov 26-30, 2001, Jaipur, Indi
Interplay between soft and hard hadronic components for identified hadrons in relativistic heavy ion collisions
We investigate the transverse dynamics in Au+Au collisions at \sqrt{s_NN}=200
GeV by emphasis upon the interplay between soft and hard components through p_T
dependences of particle spectra, ratios of yields, suppression factors, and
elliptic flow for identified hadrons. From hydrodynamics combined with
traversing minijets which go through jet quenching in the hot medium, we
calculate interactions of hard jets with the soft hydrodynamic components. It
is shown by the explicit dynamical calculations that the hydrodynamic radial
flow and the jet quenching of hard jets are the keys to understand the
differences among the hadron spectra for pions, kaons, and protons. This leads
to the natural interpretation for N_p/N_\pi ~ 1, R_{AA} >~ 1 for protons, and
v_2^p > v_2^\pi recently observed in the intermediate transverse momentum
region at Relativistic Heavy Ion Collider (RHIC).Comment: 11 pages, 9 figures; some references added; title changed, some data
points included in figure
Exact Analysis of Entanglement in Gapped Quantum Spin Chains
We investigate the entanglement properties of the valence-bond-solid states
with generic integer-spin . Using the Schwinger boson representation of the
valence-bond-solid states, the entanglement entropy, the von Neumann entropy of
a subsystem, is obtained exactly and its relationship with the usual
correlation function is clarified. The saturation value of the entanglement
entropy, , is derived explicitly and is interpreted in terms of
the edge-state picture. The validity of our analytical results and the
edge-state picture is numerically confirmed. We also propose a novel
application of the edge state as a qubit for quantum computation.Comment: 4 pages, 2 figure
A High Stellar Obliquity in the WASP-7 Exoplanetary System
We measure a tilt of 86+-6 deg between the sky projections of the rotation
axis of the WASP-7 star, and the orbital axis of its close-in giant planet.
This measurement is based on observations of the Rossiter-McLaughlin (RM)
effect with the Planet Finder Spectrograph on the Magellan II telescope. The
result conforms with the previously noted pattern among hot-Jupiter hosts,
namely, that the hosts lacking thick convective envelopes have high
obliquities. Because the planet's trajectory crosses a wide range of stellar
latitudes, observations of the RM effect can in principle reveal the stellar
differential rotation profile; however, with the present data the signal of
differential rotation could not be detected. The host star is found to exhibit
radial-velocity noise (``stellar jitter') with an amplitude of ~30m/s over a
timescale of days.Comment: ApJ accepted, 9 pages, 9 figure
Unified description of Bjorken and Landau 1+1 hydrodynamics
We propose a generalization of the Bjorken in-out Ansatz for fluid
trajectories which, when applied to the (1+1) hydrodynamic equations, generates
a one-parameter family of analytic solutions interpolating between the
boost-invariant Bjorken picture and the non boost-invariant one by Landau. This
parameter characterises the proper-time scale when the fluid velocities
approach the in-out Ansatz. We discuss the resulting rapidity distribution of
entropy for various freeze-out conditions and compare it with the original
Bjorken and Landau results.Comment: 20 pages, 5 figure
Search for the onset of baryon anomaly at RHIC-PHENIX
The baryon production mechanism at the intermediate (2 - 5 GeV/) at
RHIC is still not well understood. The beam energy scan data in Cu+Cu and Au+Au
systems at RHIC may provide us a further insight on the origin of the baryon
anomaly and its evolution as a function of . In 2005 RHIC
physics program, the PHENIX experiment accumulated the first intensive low beam
energy data in Cu+Cu collisions. We present the preliminary results of
identified charged hadron spectra in Cu+Cu at = 22.5 and 62.4
GeV using the PHENIX detector. The centrality and beam energy dependences of
(anti)proton to pion ratios and the nuclear modification factors for charged
pions and (anti)protons are presented.Comment: 5 pages, 9 figures, proceedings for Hot Quarks 2006 workshop,
Villasimius, Sardinia, Italy, May 15 - 20, 2006. Proceedings of the
conference will be published in The European Physical Journal
The eccentricity in heavy-ion collisions from Color Glass Condensate initial conditions
The eccentricity in coordinate-space at midrapidity of the overlap zone in
high-energy heavy-ion collisions predicted by the -factorization
formalism is generically larger than expected from scaling with the number of
participants. We provide a simple qualitative explanation of the effect which
shows that it is not caused predominantly by edge effects. We also show that it
is quite insensitive to ``details'' of the unintegrated gluon distribution
functions such as the presence of leading-twist shadowing and of an extended
geometric scaling window. The larger eccentricity increases the azimuthal
asymmetry of high transverse momentum particles. Finally, we point out that the
longitudinal structure of the Color Glass Condensate initial condition for
hydrodynamics away from midrapidity is non-trivial but requires understanding
of large- effects.Comment: 8 pages, 7 figures; v3: added note regarding Qs2~n_part versus
Qs2~T_A, final version to appear in PR
Unitary Theory of Evaporating 2D Black Holes
We study a manifestly unitary formulation of 2d dilaton quantum gravity based
on the reduced phase space quantization. The spacetime metric can be expanded
in a formal power series of the matter energy-momentum tensor operator. This
expansion can be used for calculating the quantum corrections to the classical
black hole metric by evaluating the expectation value of the metric operator in
an appropriate class of the physical states. When the normal ordering in the
metric operator is chosen to be with respect to Kruskal vacuum, the lowest
order semiclassical metric is exactly the one-loop effective action metric
discovered by Bose, Parker and Peleg. The corresponding semiclassical geometry
describes an evaporating black hole which ends up as a remnant. The calculation
of higher order corrections and implications for the black hole fate are
discussed.Comment: LaTex fil
CGC, Hydrodynamics, and the Parton Energy Loss
Hadron spectra in Au+Au collisions at RHIC are calculated by hydrodynamics
with initial conditions from the Color Glass Condensate (CGC). Minijet
components with parton energy loss in medium are also taken into account by
using parton density obtained from hydrodynamical simulations. We found that
CGC provides a good initial condition for hydrodynamics in Au+Au collisions at
RHIC.Comment: Quark Matter 2004 contribution, 4 pages, 2 figure
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