3,230 research outputs found
ATLAS results on top properties
Recent measurements of top quark properties using events produced
in proton-proton collisions at the Large Hadron Collider with centre of mass
energies of 7 and 8 TeV and detected by the ATLAS experiment are presented.
These results include top quark mass, the top and anti-top mass difference, the
electric charge, the top quark polarization and spin correlation, the charge asymmetry and the search for flavour changing neutral currents.Comment: 6 pages. Proceedings of presentation at the The Second Annual
Conference on Large Hadron Collider Physics, Columbia University, New York,
U.S.A, June 2-7, 2014, On behalf of the ATLAS Collaboratio
Observation of Microlensing towards the Galactic Spiral Arms. EROS II 2 year survey
We present the analysis of the light curves of 8.5 million stars observed
during two seasons by EROS (Experience de Recherche d'Objets Sombres), in the
galactic plane away from the bulge. Three stars have been found that exhibit
luminosity variations compatible with gravitational microlensing effects due to
unseen objects. The corresponding optical depth, averaged over four directions,
is 0.38 (+0.53, -0.15) 10^{-6}. All three candidates have long Einstein radius
crossing times ( 70 to 100 days). For one of them, the lack of evidence
for a parallax or a source size effect enabled us to constrain the lens-source
% geometric configuration. Another candidate displays a modulation of the
magnification, which is compatible with the lensing of a binary source.
The interpretation of the optical depths inferred from these observations is
hindered by the imperfect knowledge of the distance to the target stars. Our
measurements are compatible with expectations from simple galactic models under
reasonable assumptions on the target distances.Comment: 11 pages, 13 figures, accepted by A&A in Aug 9
B-physics overview in ATLAS
An overview of the ATLAS B-physics trigger and offline performance studies are p resented. From the initial running at low luminosity at LHC, high-statistics B a nalyses will allow sensitive tests of possible new physics contributions by sear ching for additional CP violating effects and for anomalous rates of rare B-deca y channels. In the physics of the meson system the expected sensitiv ity to mass and width differences are compared to recent measurements done at th e Tevatron. There is also sensitivity to a weak mixing phase beyond the Standard Model expectation. ATLAS will also be able to access rare B decays using the high luminosity running
RETROCAM: A Versatile Optical Imager for Synoptic Studies
We present RETROCAM, an auxiliary CCD camera that can be rapidly inserted
into the optical beam of the MDM 2.4m telescope. The speed and ease of
reconfiguring the telescope to use the imager and a straightforward user
interface permit the camera to be used during the course of other observing
programs. This in turn encourages RETROCAM's use for a variety of monitoring
projects.Comment: 6 pages, 6 figures, Accepted by A
Observation of periodic variable stars towards the galactic spiral arms by EROS II
We present the results of a massive variability search based on a photometric
survey of a six square degree region along the Galactic plane at (, ) and (, ). This
survey was performed in the framework of the EROS II (Exp\'erience de Recherche
d'Objets Sombres) microlensing program. The variable stars were found among
1,913,576 stars that were monitored between April and June 1998 in two
passbands, with an average of 60 measurements. A new period-search technique is
proposed which makes use of a statistical variable that characterizes the
overall regularity of the flux versus phase diagram. This method is well suited
when the photometric data are unevenly distributed in time, as is our case.
1,362 objects whose luminosity varies were selected. Among them we identified 9
Cepheids, 19 RR Lyrae, 34 Miras, 176 eclipsing binaries and 266 Semi-Regular
stars. Most of them are newly identified objects. The cross-identification with
known catalogues has been performed. The mean distance of the RR Lyrae is
estimated to be kpc undergoing an average absorption of
magnitudes. This distance is in good agreement with the one
of disc stars which contribute to the microlensing source star population.Our
catalogue and light curves are available electronically from the CDS,
Strasbourg and from our Web site http://eros.in2p3.fr.Comment: 15 pages, 11 figures, accepted in A&A (april 2002
Characterization of Gravitational Microlensing Planetary Host Stars
The gravitational microlensing light curves that reveal the presence of
extrasolar planets generally yield the planet-star mass ratio and separation in
units of the Einstein ring radius. The microlensing method does not require the
detection of light from the planetary host star. This allows the detection of
planets orbiting very faint stars, but it also makes it difficult to convert
the planet-star mass ratio to a value for the planet mass. We show that in many
cases, the lens stars are readily detectable with high resolution space-based
follow-up observations in a single passband. When the lens star is detected,
the lens-source relative proper motion can also be measured, and this allows
the masses of the planet and its host star to be determined and the star-planet
separation can be converted to physical units. Observations in multiple
passbands provide redundant information, which can be used to confirm this
interpretation. For the recently detected super-Earth planet,
OGLE-2005-BLG-169Lb, we show that the lens star will definitely be detectable
with observations by the Hubble Space Telescope (HST) unless it is a stellar
remnant. Finally, we show that most planets detected by a space-based
microlensing survey are likely to orbit host stars that will be detected and
characterized by the same survey.Comment: accepted for publication in ApJ, May 10, 200
Improving the Prospects for Detecting Extrasolar Planets in Gravitational Microlensing in 2002
Gravitational microlensing events of high magnification have been shown to be
promising targets for detecting extrasolar planets. However, only a few events
of high magnification have been found using conventional survey techniques.
Here we demonstrate that high magnification events can be readily found in
microlensing surveys using a strategy that combines high frequency sampling of
target fields with online difference imaging analysis. We present 10
microlensing events with peak magnifications greater than 40 that were detected
in real-time towards the Galactic Bulge during 2001 by MOA. We show that Earth
mass planets can be detected in future events such as these through intensive
follow-up observations around the event peaks. We report this result with
urgency as a similar number of such events are expected in 2002.Comment: 11 pages, 3 embedded ps figures including 2 colour, revised version
accepted by MNRA
Discovery of a peculiar Cepheid-like star towards the northern edge of the Small Magellanic Cloud
For seven years, the EROS-2 project obtained a mass of photometric data on
variable stars. We present a peculiar Cepheid-like star, in the direction of
the Small Magellanic Cloud, which demonstrates unusual photometric behaviour
over a short time interval. We report on data of the photometry acquired by the
MARLY telescope and spectroscopy from the EFOSC instrument for this star,
called EROS2 J005135-714459(sm0060n13842), which resembles the unusual Cepheid
HR 7308. The light curve of our target is analysed using the Analysis of
Variance method to determine a pulsational period of 5.5675 days. A fit of
time-dependent Fourier coefficients is performed and a search for proper motion
is conducted. The light curve exhibits a previously unobserved and spectacular
change in both mean magnitude and amplitude, which has no clear theoretical
explanation. Our analysis of the spectrum implies a radial velocity of 104 km
s and a metallicity of -0.40.2 dex. In the direction of right
ascension, we measure a proper motion of 17.46.0 mas yr using EROS
astrometry, which is compatible with data from the NOMAD catalogue. The nature
of EROS2 J005135-714459(sm0060n13842) remains unclear. For this star, we may
have detected a non-zero proper motion for this star, which would imply that it
is a foreground object. Its radial velocity, pulsational characteristics, and
photometric data, however, suggest that it is instead a Cepheid-like object
located in the SMC. In such a case, it would present a challenge to
conventional Cepheid models.Comment: Correction of typos in the abstrac
The Wendelstein Calar Alto Pixellensing Project(WeCAPP): First MACHO Candidates
We report the detection of the first 2 microlensing candidates from the
Wendelstein Calar Alto Pixellensing Project (WeCAPP). Both are detected with a
high signal-to-noise-ratio and were filtered out from 4.5 mill. pixel light
curves using a variety of selection criteria. Here we only consider
well-sampled events with timescales of 1 d < t_fwhm < 20 d, high amplitude, and
low chi^2 of the microlensing fit. The two-color photometry (R,I) shows that
the events are achromatic and that giant stars with colors of (R-I) ~ 1.1 mag
in the bulge of M31 have been lensed. The magnification factors are 64 and 10
which are obtained for typical giant luminosities of M_I = -2.5 mag. Both
lensing events lasted for only a few days (t_fwhm^GL1 = 1.7 d and t_fwhm^GL2 =
5.4 d). The event GL1 is likely identical with PA-00-S3 reported by the
POINT-AGAPE project. Our calculations favor in both cases the possibility that
MACHOs in the halo of M31 caused the lensing events. The most probable masses,
0.08 M_sun for GL1 and 0.02 M_sun for GL2, are in the range of the brown dwarf
limit of hydrogen burning. Solar mass objects are a factor of two less likely.Comment: Accepted for publication in ApJ Letters (28 Oct 2003), 4 pages, 2
color figures, uses emulateapj styl
MACHO 96-LMC-2: Lensing of a Binary Source in the LMC and Constraints on the Lensing Object
We present photometry and analysis of the microlensing alert MACHO 96-LMC-2.
The ~3% photometry provided by the Global Microlensing Alert Network follow--up
effort reveals a periodic modulation in the lightcurve. We attribute this to
binarity of the lensed source. Microlensing fits to a rotating binary source
magnified by a single lens converge on two minima, separated by delta chi^2 ~
1. The most significant fit X1 predicts a primary which contributes ~100% of
the light, a dark secondary, and an orbital period (T) of 9.2 days. The second
fit X2 yields a binary source with two stars of roughly equal mass and
luminosity, and T = 21.2 days.
The lensed object appears to lie on the upper LMC main sequence. We estimate
the mass of the primary component of the binary system, M ~2 M_sun. For the
preferred model X1, we explore the range of dark companions by assuming 0.1
M_sun and 1.4 M_sun objects in models X1a and X1b, respectively. We find lens
velocities projected to the LMC in these models of v^hat_X1a = 18.3 +/- 3.1
km/s and v^hat_X1b = 188 +/- 32 k/ms. In both these cases, a likelihood
analysis suggests an LMC lens is preferred over a Galactic halo lens, although
only marginally so in model X1b. We also find v^hat_X2 = 39.6 +/- 6.1 k/ms,
where the likelihood for the lens location is strongly dominated by the LMC
disk. In all cases, the lens mass is consistent with that of an M-dwarf. The
LMC self-lensing rate contributed by 96-LMC-2 is consistent with model
self-lensing rates. (Abridged)Comment: 23 pages, including 3 tables and 6 figures; Accepted for publication
in The Astrophysical Journa
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