10,371 research outputs found
Angular correlations in single-top-quark and Wjj production at next-to-leading order
I demonstrate that the correlated angular distributions of final-state
particles in both single-top-quark production and the dominant Wjj backgrounds
can be reliably predicted. Using these fully-correlated angular distributions,
I propose a set of cuts that can improve the single-top-quark discovery
significance by 25%, and the signal to background ratio by a factor of 3 with
very little theoretical uncertainty. Up to a subtlety in t-channel
single-top-quark production, leading-order matrix elements are shown to be
sufficient to reproduce the next-to-leading order correlated distributions.Comment: 22 pages, 23 figs, RevTex4, fixed typos, to appear in Phys. Rev.
Using Charge Asymmetries to Measure Single Top Quark Production at the LHC
Electroweak production of single top quarks is an as-yet-unverified
prediction of the Standard model, potentially sensitive to new physics. Two of
the single top quark productions channels have significant charge asymmetries
at the LHC, while the much larger background from is nearly
charge-symmetric. This can be used to reduce systematic uncertainties and make
precision measurements of single top quark production.Comment: 4 pages, 1 figur
The Detection of Lyman-alpha Absorption from Nine Nearby Galaxies
We have used STIS aboard HST to search for Lyman-alpha (Lya) absorption in
the outer regions of nine nearby (cz<6000 km/s) galaxies using background QSOs
and AGN as probes. The foreground galaxies are intercepted between 26 and 199
h-1 kpc from their centers, and in all cases we detect Lya within +/-500 km/s
of the galaxies' systemic velocities. The intervening galaxies have a wide
range of luminosities, from M_B = -17.1 to -20.0, and reside in various
environments: half the galaxies are relatively isolated, the remainder form
parts of groups or clusters of varying richness. The equivalent widths of the
Lya lines range from 0.08 - 0.68 A and, with the notable exception of
absorption from one pair, crudely correlate with sightline separation in a way
consistent with previously published data, though the column densities derived
from the lines do not. The lack of correlation between line strength and galaxy
luminosity or, in particular, the environment of the galaxy, suggests that the
absorption is not related to any individual galaxy, but arises in gas which
follows the same dark-matter structures that the galaxies inhabit.Comment: 8 pages, invited review to appear in the proceedings of the Yale
Cosmology Workshop on `The Shapes of Galaxies & their Halos", P. Natarajan,
ed. Best figures found in (17Mb) PS file at
http://astro.princeton.edu/~dvb/yale.p
Interstellar Mg II and C IV absorption by 1 1/2 galaxies along the sightline to MrK 205
The first results of our HST survey designed to search for Mg 2 and C 4 absorption lines from the disks and halos of low-redshift galaxies using background QSO's and supernovae as probes are presented. Our survey utilizes the high resolution of the Goddard High Resolution Spectrograph enabling us to calculate the column densities and doppler parameters of individual components within an absorption complex, and hence determine the physical conditions of the absorbing gas. Observing the complexity of the absorption line profiles i.e., the velocity distribution and total velocity extent of the constituent components, offers an important description of the kinematics of the absorbing gas, and hence an understanding of its origin. Focus is on one sight line in particular, that towards Mrk 205, which passes 3-5 kpc from the intervening galaxy NGC 4319. Mg 2 and C 4 absorption from both local Milky Way halo gas and from NGC 4319 is detected
Supporting the Mobile In-situ Authoring of Locative Media in Rural Places: Design and Expert Evaluation of the SMAT app
Providing users with carefully authored Locative media experiences (which can be consumed via their GPS equipped smartphones or tablets) has significant potential for fostering a strong engagement with their current surroundings. However, the availability of mobile tools to support the authoring of locative media experiences in-situ, and by non-technical users, remains scarce. In this article we present the design and field-trial expert evaluation of a mobile app developed under the SHARC project (Investigating Technology Support for the Shared Curation of Local History in a Rural Community). The app is named SMAT (SHARC Mobile Authoring Tool) and supports the authoring of Locative Media experiences with a focus on the creation of POIs (Points of Interest) and associated geo-fences which trigger the pushed delivery of media items such as photos, audio clips, etc. One important requirement of SMAT is the ability to support authoring in places where connectivity is intermittent or unavailable, e.g. many rural areas
A Comparison of Absorption and Emission Line Abundances in the Nearby Damped Lyman-alpha Galaxy SBS 1543+593
We have used the Space Telescope Imaging Spectrograph (STIS) aboard HST to
measure a sulfur abundance of [S/H] = -0.41 +/-0.06 in the interstellar medium
(ISM) of the nearby damped Lyman-alpha (DLA) absorbing galaxy SBS 1543+593. A
direct comparison between this QSO absorption line abundance on the one hand,
and abundances measured from HII region emission line diagnostics on the other,
yield the same result: the abundance of sulfur in the neutral ISM is in good
agreement with that of oxygen measured in an HII region 3 kpc away. Our result
contrasts with those of other recent studies which have claimed
order-of-magnitude differences between HI (absorption) and HII (emission)
region abundances. We also derive a nickel abundance of [Ni/H] < -0.81, some
three times less than that of sulfur, and suggest that the depletion is due to
dust, although we cannot rule out an over-abundance of alpha-elements as the
cause of the lower metallicity. It is possible that our measure of [S/H] is
over-estimated if some SII arises in ionized gas; adopting a plausible star
formation rate for the galaxy along the line of sight, and a measurement of the
CII* 1335.7 absorption line detected from SBS 1543+593, we determine that the
metallicity is unlikely to be smaller than we derive by more than 0.25 dex. We
estimate that the cooling rate of the cool neutral medium is log [l_c (ergs
s^{-1} H atom^{-1})] = -27.0, the same value as that seen in the high redshift
DLA population.Comment: 31 pages; accepted for publication in the Ap
Redshifts of galaxies close to bright QSO lines of sight
To expand the known number of low-redshift galaxies which lie close to bright
() QSO lines of sight, we have identified 24 galaxies within 11
arcmins of nine QSOs which have been observed with the Hubble Space Telescope
(HST). Galaxies are found between redshifts of and lie between
kpc from QSO sightlines. Knowing the redshifts of these
galaxies has already proved important in understanding results from HST
programmes designed to search for UV absorption lines from low-redshift
galaxies, and will enable future observations to probe the halos of these
galaxies in detail.Comment: MNRAS in press. 9 pages LaTeX using MNRAS sty. Postscript figures are
excluded due to large size. Paper with figures can be obtained from
http://www.roe.ac.uk/research/bowen1.ps.
Teleportation of continuous variable polarisation states
This paper discusses methods for the optical teleportation of continuous
variable polarisation states. We show that using two pairs of entangled beams,
generated using four squeezed beams, perfect teleportation of optical
polarisation states can be performed. Restricting ourselves to 3 squeezed
beams, we demonstrate that polarisation state teleportation can still exceed
the classical limit. The 3-squeezer schemes involve either the use of quantum
non-demolition measurement or biased entanglement generated from a single
squeezed beam. We analyse the efficacies of these schemes in terms of fidelity,
signal transfer coefficients and quantum correlations
21-cm H I emission from the Damped Lyman-alpha absorber SBS 1543+593
We detect 21-cm emission from the Low Surface Brightness (LSB) galaxy SBS
1543+593, which gives rise to a Damped Lyman-alpha (DLA) absorption line in the
spectrum of the background QSO HS 1543+5921 (z=0.807). We obtain an accurate
measure of the velocity of the H I gas in the LSB galaxy, v=2868 km/s, and
derive a mass of 1.3e9 solar masses. We compare this value with limits obtained
towards two other z~0.1 DLA systems, and show that SBS 1543+593 would not have
been detected. Hence LSB galaxies similar to SBS 1543+593 can be responsible
for DLA systems at even modest redshifts without being detectable from their
21-cm emission.Comment: 4 pages, 1 figure, accepted for publication in A&
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