11,396 research outputs found
Small optic suspensions for Advanced LIGO input optics and other precision optical experiments
We report on the design and performance of small optic suspensions developed
to suppress seismic motion of out-of-cavity optics in the Input Optics
subsystem of the Advanced LIGO interferometric gravitational wave detector.
These compact single stage suspensions provide isolation in all six degrees of
freedom of the optic, local sensing and actuation in three of them, and passive
damping for the other three
Characterization of thermal effects in the Enhanced LIGO Input Optics
We present the design and performance of the LIGO Input Optics subsystem as
implemented for the sixth science run of the LIGO interferometers. The Initial
LIGO Input Optics experienced thermal side effects when operating with 7 W
input power. We designed, built, and implemented improved versions of the Input
Optics for Enhanced LIGO, an incremental upgrade to the Initial LIGO
interferometers, designed to run with 30 W input power. At four times the power
of Initial LIGO, the Enhanced LIGO Input Optics demonstrated improved
performance including better optical isolation, less thermal drift, minimal
thermal lensing and higher optical efficiency. The success of the Input Optics
design fosters confidence for its ability to perform well in Advanced LIGO
Deep inelastic events containing a forward photon as a probe of small dynamics
We calculate the rate of producing deep inelastic events containing an
energetic isolated forward photon at HERA. We quantify the enhancement arising
from the leading gluon emissions with a view to using such events to
identify the underlying dynamics.Comment: 11 pages, Latex, 7 ps figure
A Survey for Massive Giant Planets in Debris Disks with Evacuated Inner Cavities
The commonality of collisionally replenished debris around main sequence
stars suggests that minor bodies are frequent around Sun-like stars. Whether or
not debris disks in general are accompanied by planets is yet unknown, but
debris disks with large inner cavities - perhaps dynamically cleared - are
considered to be prime candidates for hosting large-separation massive giant
planets. We present here a high-contrast VLT/NACO angular differential imaging
survey for eight such cold debris disks. We investigated the presence of
massive giant planets in the range of orbital radii where the inner edge of the
dust debris is expected. Our observations are sensitive to planets and brown
dwarfs with masses >3 to 7 Jupiter mass, depending on the age and distance of
the target star. Our observations did not identify any planet candidates. We
compare the derived planet mass upper limits to the minimum planet mass
required to dynamically clear the inner disks. While we cannot exclude that
single giant planets are responsible for clearing out the inner debris disks,
our observations constrain the parameter space available for such planets. The
non-detection of massive planets in these evacuated debris disks further
reinforces the notion that the giant planet population is confined to the inner
disk (<15 AU).Comment: Accepted for publication in Ap
Parity Violation in gamma proton Compton Scattering
A measurement of parity-violating spin-dependent gamma proton Compton
scattering will provide a theoretically clean determination of the
parity-violating pion-nucleon coupling constant . We
calculate the leading parity-violating amplitude arising from one-loop pion
graphs in chiral perturbation theory. An asymmetry of ~5 10^{-8} is estimated
for Compton scattering of 100 MeV photons.Comment: 6 pages, 1 figure, latex. Reference adde
Theoretical issues of small physics
The perturbative QCD predictions concerning deep inelastic scattering at low
are summarized. The theoretical framework based on the leading log
resummation and factorization theorem is described and some recent
developments concerning the BFKL equation and its generalization are discussed.
The QCD expectations concerning the small behaviour of the spin dependent
structure function are briefly summarized and the importance of
the double logarithmic terms which sum contributions containing the leading
powers of is emphasised. The role of studying final states
in deep inelastic scattering for revealing the details of the underlying
dynamics at low is pointed out and some dedicated measurements, like deep
inelastic scattering accompanied by an energetic jet, the measurement of the
transverse energy flow etc., are briefly discussed.Comment: 17 pages, LATEX, 7 uuencoded eps figures include
Diffractive Leptoproduction of Vector Mesons in QCD
We demonstrate that the distinctive features of the forward differential
cross section of diffractive leptoproduction of a vector meson can be
legitimately calculated in perturbative QCD in terms of the light-cone wave function of the vector meson and the gluon distribution of the target.
In particular, we calculate the and nuclear dependence of the diffractive
leptoproduction of vector mesons and estimate the cross section. The production
of longitudinally polarized vector mesons by longitudinally polarized virtual
photons is predicted to be the dominant component, yielding a cross section
behaving as . The nuclear dependence of the diffractive cross sections,
which follows from a factorization theorem in perturbative QCD, provides
important tests of color transparency as well as constraints on the shadowing
of the gluon structure functions and the longitudinal structure functions of
nuclei.Comment: 32 pages, requires phyzzx.tex, figures can be obtained by sending
preprint request to SLAC, minor clarifications and additional references
incorporated in revised version, preprint SLAC-PUB-641
Quark Orbital-Angular-Momentum Distribution in the Nucleon
We introduce gauge-invariant quark and gluon angular momentum distributions
after making a generalization of the angular momentum density operators. From
the quark angular momentum distribution, we define the gauge-invariant and
leading-twist quark {\it orbital} angular momentum distribution . The
latter can be extracted from data on the polarized and unpolarized quark
distributions and the off-forward distribution in the forward limit. We
comment upon the evolution equations obeyed by this as well as other orbital
distributions considered in the literature.Comment: 8 pages, latex, no figures, minor corrections mad
Observable jets from the BFKL chain
We derive a modified form of the BFKL equation which enables the structure of
the gluon emissions to be studied in small deep inelastic scattering. The
equation incorporates the resummation of the virtual and unresolved real gluon
emissions. We solve the equation to calculate the number of small
deep-inelastic events containing 0,1,2 ...resolved gluon jets, that is jets
with transverse momenta . We study the jet decomposition for
different choices of the jet resolution parameter .Comment: 14 pages, Latex, 13 ps figure
New measurement of the scattering cross section of slow neutrons on liquid parahydrogen from neutron transmission
Liquid hydrogen is a dense Bose fluid whose equilibrium properties are both
calculable from first principles using various theoretical approaches and of
interest for the understanding of a wide range of questions in many body
physics. Unfortunately, the pair correlation function inferred from
neutron scattering measurements of the differential cross section from different measurements reported in the literature are
inconsistent. We have measured the energy dependence of the total cross section
and the scattering cross section for slow neutrons with energies between
0.43~meV and 16.1~meV on liquid hydrogen at 15.6~K (which is dominated by the
parahydrogen component) using neutron transmission measurements on the hydrogen
target of the NPDGamma collaboration at the Spallation Neutron Source at Oak
Ridge National Laboratory. The relationship between the neutron transmission
measurement we perform and the total cross section is unambiguous, and the
energy range accesses length scales where the pair correlation function is
rapidly varying. At 1~meV our measurement is a factor of 3 below the data from
previous work. We present evidence that these previous measurements of the
hydrogen cross section, which assumed that the equilibrium value for the ratio
of orthohydrogen and parahydrogen has been reached in the target liquid, were
in fact contaminated with an extra non-equilibrium component of orthohydrogen.
Liquid parahydrogen is also a widely-used neutron moderator medium, and an
accurate knowledge of its slow neutron cross section is essential for the
design and optimization of intense slow neutron sources. We describe our
measurements and compare them with previous work.Comment: Edited for submission to Physical Review
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