111,311 research outputs found
What can we learn from Dijet suppression at RHIC?
We present a systematic study of the dijet suppression at RHIC using the
VNI/BMS parton cascade. We examine the modification of the dijet asymmetry A_j
and the within-cone transverse energy distribution (jet-shape) along with
partonic fragmentation distributions z and j_t in terms of: qhat; the path
length of leading and sub-leading jets; cuts on the jet energy distributions;
jet cone angle and the jet-medium interaction mechanism. We find that A_j is
most sensitive to qhat and relatively insensitive to the nature of the
jet-medium interaction mechanism. The jet profile is dominated by qhat and the
nature of the interaction mechanism. The partonic fragmentation distributions
clearly show the jet modification and differentiate between elastic and
radiative+elastic modes
Jet Modification in a Brick of QGP Matter
We have implemented the LPM effect into a microscopic transport model with
partonic degrees of freedom by following the algorithm of Zapp & Wiedemann. The
Landau-Pomeranchuk-Migdal (LPM) effect is a quantum interference process that
modifies the emission of radiation in the presence of a dense medium. In QCD
this results in a quadratic length dependence for radiative energy loss. This
is an important effect for the modification of jets by their passage through
the QGP.
We verify the leading parton energy loss in the model against the leading
order Baier-Dokshitzer-Mueller-Peigne-Schiff-Zakharov (BDMPS-Z) result.
We apply our model to the recent observations of the modification of di-jets
at the LHC.Comment: Presented at Panic 1
X-ray Dust Scattering at Small Angles: The Complete Halo around GX13+1
The exquisite angular resolution available with Chandra should allow
precision measurements of faint diffuse emission surrounding bright sources,
such as the X-ray scattering halos created by interstellar dust. However, the
ACIS CCDs suffer from pileup when observing bright sources, and this creates
difficulties when trying to extract the scattered halo near the source. The
initial study of the X-ray halo around GX13+1 using only the ACIS-I detector
done by Smith, Edgar & Shafer (2002) suffered from a lack of sensitivity within
50'' of the source, limiting what conclusions could be drawn.
To address this problem, observations of GX13+1 were obtained with the
Chandra HRC-I and simultaneously with the RXTE PCA. Combined with the existing
ACIS-I data, this allowed measurements of the X-ray halo between 2-1000''.
After considering a range of dust models, each assumed to be smoothly
distributed with or without a dense cloud along the line of sight, the results
show that there is no evidence in this data for a dense cloud near the source,
as suggested by Xiang et al. (2005). Finally, although no model leads to
formally acceptable results, the Weingartner & Draine (2001) and nearly all of
the composite grain models from Zubko, Dwek & Arendt (2004) give poor fits.Comment: 8 pages, 6 figures, accepted for publication in Ap
Topological states in multi-orbital HgTe honeycomb lattices
Research on graphene has revealed remarkable phenomena arising in the
honeycomb lattice. However, the quantum spin Hall effect predicted at the K
point could not be observed in graphene and other honeycomb structures of light
elements due to an insufficiently strong spin-orbit coupling. Here we show
theoretically that 2D honeycomb lattices of HgTe can combine the effects of the
honeycomb geometry and strong spin-orbit coupling. The conduction bands,
experimentally accessible via doping, can be described by a tight-binding
lattice model as in graphene, but including multi-orbital degrees of freedom
and spin-orbit coupling. This results in very large topological gaps (up to 35
meV) and a flattened band detached from the others. Owing to this flat band and
the sizable Coulomb interaction, honeycomb structures of HgTe constitute a
promising platform for the observation of a fractional Chern insulator or a
fractional quantum spin Hall phase.Comment: includes supplementary materia
Tuning the effects of Landau-level mixing on anisotropic transport in quantum Hall systems
Electron-electron interactions in half-filled high Landau levels in
two-dimensional electron gases in a strong perpendicular magnetic field can
lead to states with anisotropic longitudinal resistance. This longitudinal
resitance is generally believed to arise from broken rotational invariance,
which is indicated by charge density wave (CDW) order in Hartree-Fock
calculations. We use the Hartree-Fock approximation to study the influence of
externally tuned Landau level mixing on the formation of interaction induced
states that break rotational invariance in two-dimensional electron and hole
systems. We focus on the situation when there are two non-interacting states in
the vicinity of the Fermi level and construct a Landau theory to study coupled
charge density wave order that can occur as interactions are tuned and the
filling or mixing are varied. We examine in detail a specific example where
mixing is tuned externally through Rashba spin-orbit coupling. We calculate the
phase diagram and find the possibility of ordering involving coupled striped or
triangular charge density waves in the two levels. Our results may be relevant
to recent transport experiments on quantum Hall nematics in which Landau-level
mixing plays an important role.Comment: 25 pages, 6 figure
Stellar Populations in the Phoenix Dwarf (dIrr/dSph) Galaxy as Observed by HST/WFPC2
We present HST/WFPC2 photometry of the central regions of the Phoenix dwarf.
Accurate photometry allows us to: 1) confirm the existence of the horizontal
branch previously detected by ground-based observations, and use it to
determine a distance to Phoenix, 2) clearly detect the existence of multiple
ages in the stellar population of Phoenix, 3) determine a mean metallicity of
the old red giant branch stars in Phoenix, and suggest that Phoenix has evolved
chemically over its lifetime, 4) extract a rough star formation history for the
central regions which suggests that Phoenix has been forming stars roughly
continuously over its entire lifetime.Comment: Accepted by AJ, 22 pages including 6 figures + 1 figure in JPEG
forma
Exact Results for Three-Body Correlations in a Degenerate One-Dimensional Bose Gas
Motivated by recent experiments we derive an exact expression for the
correlation function entering the three-body recombination rate for a
one-dimensional gas of interacting bosons. The answer, given in terms of two
thermodynamic parameters of the Lieb-Liniger model, is valid for all values of
the dimensionless coupling and contains the previously known results
for the Bogoliubov and Tonks-Girardeau regimes as limiting cases. We also
investigate finite-size effects by calculating the correlation function for
small systems of 3, 4, 5 and 6 particles.Comment: 4 pages, 2 figure
Very high two-dimensional hole gas mobilities in strained silicon germanium
We report on the growth by solid source MBE and characterization of remote doped Si/SiGe/Si two-dimensional hole gas structures. It has been found that by reducing the Ge composition to <=13% and limiting the thickness of the alloy layer, growth temperatures can be increased up to 950 °C for these structures while maintaining good structural integrity and planar interfaces. Record mobilities of 19 820 cm2 V−1 s−1 at 7 K were obtained in normal structures. Our calculations suggest that alloy scattering is not important in these structures and that interface roughness and interface charge scattering limit the low temperature mobilities
Quasi-Particle Spectra, Charge-Density-Wave, Superconductivity and Electron-Phonon Coupling in 2H-NbSe2
High-resolution photoemission has been used to study the electronic structure
of the charge density wave (CDW) and superconducting (SC) dichalcogenide, 2H-
NbSe2. From the extracted self-energies, important components of the
quasiparticle (QP) interactions have been identified. In contrast to previously
studied TaSe2, the CDW transition does not affect the electronic properties
significantly. The electron-phonon coupling is identified as a dominant
contribution to the QP self-energy and is shown to be very anisotropic
(k-dependent) and much stronger than in TaSe2.Comment: 4 pages, 3 figures, minor changes, to appear in PR
- …