1,477 research outputs found
Precise measurement of the total cross section and the Coulomb scattering at the LHC
A precise measurement of the total cross section and the coulomb scattering
at the LHC requires the observation of elastically scatteredparticles at
extremely small angles (14 microrad, -t < 0.01 GeV**2 for the first case; 3
microrad, -t<0.0006 GeV**2 for the second one). In this paper a very high-beta
insertion optics is presented. A feasibility study, including the acceptance of
the detectors, for an experiment to be installed in IR1 or IR5, is also
presented.Comment: 3 pages, 4 figures, 7th European Particle Accelator Conferenc
First result with AMBER+FINITO on the VLTI: The high-precision angular diameter of V3879 Sgr
Our goal is to demonstrate the potential of the interferometric AMBER
instrument linked with the Very Large Telescope Interferometer (VLTI)
fringe-tracking facility FINITO to derive high-precision stellar diameters. We
use commissioning data obtained on the bright single star V3879 Sgr. Locking
the interferometric fringes with FINITO allows us to record very low contrast
fringes on the AMBER camera. By fitting the amplitude of these fringes, we
measure the diameter of the target in three directions simultaneously with an
accuracy of 25 micro-arcseconds. We showed that V3879 Sgr has a round
photosphere down to a sub-percent level. We quickly reached this level of
accuracy because the technique used is independent from absolute calibration
(at least for baselines that fully span the visibility null). We briefly
discuss the potential biases found at this level of precision. The proposed
AMBER+FINITO instrumental setup opens several perspectives for the VLTI in the
field of stellar astrophysics, like measuring with high accuracy the oblateness
of fast rotating stars or detecting atmospheric starspots
A Very High-beta Optics to be used for an Absolute Luminosity Determination with Forward Detectors in ATLAS
The Atlas experiment at the LHC pursues a number of different approaches to obtain an estimate of the absolute luminosity [3]. Measuring elastic scattering at very small angles (3 μrad) represents a different and complimentary approach that will improve the precision of the final luminosity estimate. In this paper we show the required very high-β optics and the detector acceptance studies
Infrared Imaging of Capella with the IOTA Closure Phase Interferometer
We present infrared aperture synthesis maps produced with the upgraded IOTA
interferometer. Michelson interferograms on the close binary system Capella
(Alpha Aur) were obtained in the H-band between 2002 November 12 and 16 using
the IONIC3 beam combiner. With baselines of 15m < B < 38m, we were able to
determine the relative position of the binary components with milliarcsecond
(mas) precision and to track their movement along the approx. 14 degree arc
covered by our observation run. We briefly describe the algorithms used for
visibility and closure phase estimation. Three different Hybrid Mapping and
Bispectrum Fitting techniques were implemented within one software framework
and used to reconstruct the source brightness distribution. By dividing our
data into subsets, the system could be mapped at three epochs, revealing the
motion of the stars. The precise position of the binary components was also
determined with model fits, which in addition revealed I_Aa/I_Ab=1.49 +/- 0.10
and apparent stellar uniform-disk (UD) diameters of Theta_Aa=8.9 +/- 0.6 mas
and Theta_Ab=5.8 +/- 0.8 mas.
To improve the u, v-plane coverage, we compensated this orbital motion by
applying a rotation-compensating coordinate transformation. The resulting
model-independent map with a beam size of 5.4 x 2.6 mas allows the resolution
of the stellar surfaces of the Capella giants themselves.Comment: Accepted by the Astronomical Journal (2005-03-21
Bright Localized Near-Infrared Emission at 1-4 AU in the AB Aurigae Disk Revealed by IOTA Closure Phases
We report on the detection of localized off-center emission at 1-4 AU in the
circumstellar environment of the young stellar object AB Aurigae. We used
closure phase measurements in the near-infrared made at the long baseline
interferometer IOTA, the first obtained on a young stellar object using this
technique. When probing sub-AU scales, all closure phases are close to zero
degrees, as expected given the previously-determined size of the AB Aurigae
inner dust disk. However, a clear closure phase signal of -3.5 +/- 0.5 degrees
is detected on one triangle containing relatively short baselines, requiring a
high degree of non-point symmetry from emission at larger (AU-sized) scales in
the disk. We have not identified any alternative explanation for these closure
phase results and demonstrate that a ``disk hot spot'' model can fit our data.
We speculate that such asymmetric near-infrared emission detected might arise
as a result of localized viscous heating due to a gravitational instability in
the AB Aurigae disk, or to the presence of a close stellar companion or
accreting sub-stellar object.Comment: Accepted by Astrophysical Journal Letter
Measurement of forward photon production cross-section in proton-proton collisions at = 13 TeV with the LHCf detector
In this paper, we report the production cross-section of forward photons in
the pseudorapidity regions of and ,
measured by the LHCf experiment with proton--proton collisions at =
13 TeV. The results from the analysis of 0.191 of data
obtained in June 2015 are compared to the predictions of several hadronic
interaction models that are used in air-shower simulations for
ultra-high-energy cosmic rays. Although none of the models agree perfectly with
the data, EPOS-LHC shows the best agreement with the experimental data among
the models.Comment: 21 pages, 4 figure
The performance of the LHCf detector for hadronic showers
The Large Hadron Collider forward (LHCf) experiment has been designed to use
the LHC to benchmark the hadronic interaction models used in cosmic-ray
physics. The LHCf experiment measures neutral particles emitted in the very
forward region of LHC collisions. In this paper, the performances of the LHCf
detectors for hadronic showers was studied with MC simulations and beam tests.
The detection efficiency for neutrons is from 60% to 70% above 500 GeV. The
energy resolutions are about 40% and the position resolution is 0.1 to 1.3mm
depend on the incident energy for neutrons. The energy scale determined by the
MC simulations and the validity of the MC simulations were examined using 350
GeV proton beams at the CERN-SPS.Comment: 15pages, 19 figure
Extreme adaptive optics imaging with a clear and well-corrected off-axis telescope sub-aperture
Rather than using an adaptive optics (AO) system to correct a telescope s
entire pupil, it can instead be used to more finely correct a smaller
sub-aperture. Indeed, existing AO systems can be used to correct a sub-aperture
1/3 to 1/2 the size of a 5-10 m telescope to extreme adaptive optics (ExAO)
levels. We discuss the potential performance of a clear off-axis well-corrected
sub-aperture (WCS), and describe our initial imaging results with a 1.5 m
diameter WCS on the Palomar Observatory s Hale telescope. These include
measured Strehl ratios of 0.92-0.94 in the infrared (2.17 microns), and 0.12 in
the B band, the latter allowing a binary of separation 0.34 arc sec to be
easily resolved in the blue. Such performance levels enable a variety of novel
observational modes, such as infrared ExAO, visible-wavelength AO, and
high-contrast coronagraphy. One specific application suggested by the high
Strehl ratio stability obtained (1%) is the measurement of planetary transits
and eclipses. Also described is a simple dark-hole experiment carried out on a
binary star, in which a comatic phase term was applied directly to the
deformable mirror, in order to shift the diffraction rings to one side of the
point spread function.Comment: accepted by Ap
- …