563 research outputs found
A high angular resolution interferometric backscatter meter
Backscatter limits many interferometric measurements, including gravitational
wave detectors, by creating spurious interference. We describe an experimental
method to directly and quantitatively measure the backscatter interference. We
derive and verify experimentally a relation between backscatter interference,
beam radius and the scattering sample bidirectional reflectance distribution
function. We also demonstrate that our method is able to measure backscatter
from high quality optics for angles as low as 500 urad with a 160 urad angular
resolution.Comment: 4 pages, 4 figure
Performance of an externally triggered gravitational-wave burst search
We present the performance of searches for gravitational wave bursts
associated with external astrophysical triggers as a function of the search sky
region. We discuss both the case of Gaussian noise and real noise of
gravitational wave detectors for arbitrary detector networks. We demonstrate
the ability to reach Gaussian limited sensitivity in real non-Gaussian data,
and show the conditions required to attain it. We find that a single sky
position search is ~20% more sensitive than an all-sky search of the same data.Comment: 9 pages, 5 figures, accepted by PR
On the background estimation by time slides in a network of gravitational wave detectors
Time shifting the outputs of Gravitational Wave detectors operating in
coincidence is a convenient way to estimate the background in a search for
short duration signals. However this procedure is limited as increasing
indefinitely the number of time shifts does not provide better estimates. We
show that the false alarm rate estimation error saturates with the number of
time shifts. In particular, for detectors with very different trigger rates
this error saturates at a large value. Explicit computations are done for 2
detectors, and for 3 detectors where the detection statistic relies on the
logical ``OR'' of the coincidences of the 3 couples in the network.Comment: accepted for publication in CQ
X-Pipeline: An analysis package for autonomous gravitational-wave burst searches
Autonomous gravitational-wave searches -- fully automated analyses of data
that run without human intervention or assistance -- are desirable for a number
of reasons. They are necessary for the rapid identification of
gravitational-wave burst candidates, which in turn will allow for follow-up
observations by other observatories and the maximum exploitation of their
scientific potential. A fully automated analysis would also circumvent the
traditional "by hand" setup and tuning of burst searches that is both
labourious and time consuming. We demonstrate a fully automated search with
X-Pipeline, a software package for the coherent analysis of data from networks
of interferometers for detecting bursts associated with GRBs and other
astrophysical triggers. We discuss the methods X-Pipeline uses for automated
running, including background estimation, efficiency studies, unbiased optimal
tuning of search thresholds, and prediction of upper limits. These are all done
automatically via Monte Carlo with multiple independent data samples, and
without requiring human intervention. As a demonstration of the power of this
approach, we apply X-Pipeline to LIGO data to search for gravitational-wave
emission associated with GRB 031108. We find that X-Pipeline is sensitive to
signals approximately a factor of 2 weaker in amplitude than those detectable
by the cross-correlation technique used in LIGO searches to date. We conclude
with the prospects for running X-Pipeline as a fully autonomous, near real-time
triggered burst search in the next LSC-Virgo Science Run.Comment: 18 pages, 10 figures. Minor edits and clarifications; added more
background on gravitational waves and detectors. To appear in New Journal of
Physics
Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV
The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of βs = 7TeV corresponding to an integrated luminosity of 38 pb-1. Jets are reconstructed with the anti-kt algorithm with distance parameters R=0. 4 or R=0. 6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pTβ₯20 GeV and pseudorapidities {pipe}Ξ·{pipe}<4. 5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}Ξ·{pipe}<0. 8) for jets with 60β€pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2β€{pipe}Ξ·{pipe}<4. 5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined. Β© 2013 CERN for the benefit of the ATLAS collaboration
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