169 research outputs found
Quantum Lifetime of Two-Dimensional Holes
The quantum lifetime of two-dimensional holes in a GaAs/AlGaAs double quantum
well is determined via tunneling spectroscopy. At low temperatures the lifetime
is limited by impurity scattering but at higher temperatures hole-hole Coulomb
scattering dominates. Our results are consistent with Fermi liquid theory, at
least up to r_s = 11. At the highest temperatures the measured width of the
hole spectral function becomes comparable to the Fermi energy. A new,
tunneling-spectroscopic, method for determining the in-plane effective mass of
the holes is also demonstrated.Comment: 5 pages, 4 figures. Published versio
Development of Hydrogen and Helium Proximity Zones around Quasars
Increasing evidence suggests that He II proximity profiles in the quasar
spectra at z ~ 3 - 4 are sensitive probes of quasar ages. But the development
of their H I counterparts is difficult to trace and remains poorly constrained.
We compare the UV spectra of 15 He II quasars with their high-resolution
optical counterparts and find a significant correlation between the sizes of He
II and H I proximity zones. The luminous quasar HE2347-4342 displays a null
proximity zone in both He II and H I, suggesting that it is extremely young
(age < 0.2 Myr). Three other quasars also display small proximity zones for He
II and H I. There is no evidence that a H I ionization zone expands
considerably faster than its He II counterpart. The results suggest that the
expansion of quasar ionizing fronts may be noticeably slower than the speed of
light, and raise the possibility of distinguishing young and old quasars from
the sizes of their H I proximity zones.Comment: To appear in The Astrophysical Journal, with 19 pages, 11 figures, 2
table
Accelerator performance analysis of the Fermilab Muon Campus
Fermilab is dedicated to hosting world-class experiments in search of new
physics that will operate in the coming years. The Muon g-2 Experiment is one
such experiment that will determine with unprecedented precision the muon
anomalous magnetic moment, which offers an important test of the Standard
Model. We describe in this study the accelerator facility that will deliver a
muon beam to this experiment. We first present the lattice design that allows
for efficient capture, transport, and delivery of polarized muon beams. We then
numerically examine its performance by simulating pion production in the
target, muon collection by the downstream beam line optics, as well as
transport of muon polarization. We finally establish the conditions required
for the safe removal of unwanted secondary particles that minimizes
contamination of the final beam.Comment: 10 p
Edge Theories for Polarized Quantum Hall States
Starting from recently proposed bosonic mean field theories for fully and
partially polarized quantum Hall states, we construct corresponding effective
low energy theories for the edge modes. The requirements of gauge symmetry and
invariance under global O(3) spin rotations, broken only by a Zeeman coupling,
imply boundary conditions that allow for edge spin waves. In the generic case,
these modes are chiral, and the spin stiffness differs from that in the bulk.
For the case of a fully polarized state, our results agree with
previous Hartree-Fock calculations.Comment: 15 pages (number of pages has been reduced by typesetting in RevTeX);
2 references adde
The Properties of Two Low Redshift O VI Absorbers and Their Associated Galaxies Toward 3C 263
Ultraviolet observations of the QSO 3C 263 (zem = 0.652) with COS and FUSE
reveal O VI absorption systems at z = 0.06342 and 0.14072 . WIYN multi-object
spectrograph observations provide information about the galaxies associated
with the absorbers. The multi-phase system at z = 0.06342 traces cool
photoionized gas and warm collisionally ionized gas associated with a L ~
0.31L* compact spiral emission line galaxy with an impact parameter of 63 kpc.
The cool photoionized gas in the absorber is well modeled with log U ~ -2.6,
log N(H) ~17.8, log n(H) ~ -3.3 and [Si/H] = -0.14\pm0.23. The collisionally
ionized gas containing C IV and O VI probably arises in cooling shock heated
transition temperature gas with log T ~ 5.5. The absorber is likely tracing
circumgalactic gas enriched by gas ejected from the spiral emission line
galaxy. The simple system at z = 0.14072 only contains O VI and broad and
narrow H I. The O VI with b = 33.4\pm11.9 km s-1 is likely associated with the
broad H I {\lambda}1215 absorption with b = 86.7\pm15.4 km s-1. The difference
in Doppler parameters implies the detection of a very large column of warm gas
with log T = 5.61(+0.16, -0.25), log N(H) = 19.54(+0.26, -0.44) and [O/H] =
-1.48 (+0.46, -0.26). This absorber is possibly associated with a 1.6L*
absorption line galaxy with an impact parameter of 617 kpc although an origin
in warm filament gas or in the halo of a fainter galaxy is more likely.Comment: Accepted by the Astrophysical Journal. 24 pages and 9 figure
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