3,838 research outputs found
Automated optical identification of a large complete northern hemisphere sample of flat spectrum radio sources with S_6cm > 200 mJy
This paper describes the automated optical APM identification of radio
sources from the Jodrell Bank - VLA Astrometric Survey (JVAS), as used for the
search for distant radio-loud quasars. The sample has been used to investigate
possible relations between optical and radio properties of flat spectrum radio
sources. From the 915 sources in the sample, 756 have an optical APM
identification at a red (e) and/or blue (o) plate,resulting in an
identification fraction of 83% with a completeness and reliability of 98% and
99% respectively. About 20% are optically identified with extended APM objects
on the red plates, e.g. galaxies. However the distinction between galaxies and
quasars can not be done properly near the magnitude limit of the POSS-I plates.
The identification fraction appears to decrease from >90% for sources with a 5
GHz flux density of >1 Jy, to <80% for sources at 0.2 Jy. The identification
fraction, in particular that for unresolved quasars, is found to be lower for
sources with steeper radio spectra. In agreement with previous studies, we find
that the quasars at low radio flux density levels also tend to have fainter
optical magnitudes, although there is a large spread. In addition, objects with
a steep radio-to-optical spectral index are found to be mainly highly polarised
quasars, supporting the idea that in these objects the polarised synchrotron
component is more prominent. It is shown that the large spread in
radio-to-optical spectral index is possibly caused by source to source
variations in the Doppler boosting of the synchrotron component [Abridged].Comment: LaTex, 17 pages, 5 gif figures, 4 tables. Accepted for publication in
MNRAS. High resolution figures can be found at http://www.roe.ac.uk/~ignas
Learning How to Count: A High Multiplicity Search for the LHC
We introduce a search technique that is sensitive to a broad class of signals
with large final state multiplicities. Events are clustered into large radius
jets and jet substructure techniques are used to count the number of subjets
within each jet. The search consists of a cut on the total number of subjets in
the event as well as the summed jet mass and missing energy. Two different
techniques for counting subjets are described and expected sensitivities are
presented for eight benchmark signals. These signals exhibit diverse
phenomenology, including 2-step cascade decays, direct three body decays, and
multi-top final states. We find improved sensitivity to these signals as
compared to previous high multiplicity searches as well as a reduced reliance
on missing energy requirements. One benefit of this approach is that it allows
for natural data driven estimates of the QCD background.Comment: 36 pages, 12 Figures, 5 Tables; journal versio
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