8,249 research outputs found
High Precision Radial Velocity Measurements in the Infrared: A First Assessment of the RV Stability of CRIRES
High precision radial velocity (RV) measurements in the near infrared are on
high demand, especially in the context of exoplanet search campaigns shifting
their interest to late type stars in order to detect planets with ever lower
mass or targeting embedded pre-main-sequence objects.
ESO is offering a new spectrograph at the VLT -- CRIRES -- designed for high
resolution near-infrared spectroscopy with a comparably broad wavelength
coverage and the possibility to use gas-cells to provide a stable RV
zero-point.
We investigate here the intrinsic short-term RV stability of CRIRES, both
with gas-cell calibration data and on-sky measurements using the absorption
lines of the Earth's atmosphere imprinted in the source spectrum as a local RV
rest frame. Moreover, we also investigate for the first time the intrinsic
stability of telluric lines at 4100 nm for features originating in the lower
troposphere.
Our analysis of nearly 5 hours of consecutive observations of MS Vel, a M2II
bright giant centred at two SiO first overtone band-heads at 4100 nm,
demonstrates that the intrinsic short-term stability of CRIRES is very high,
showing only a slow and fully compensateable drift of up to 60 m/s after 4.5
hours. The radial velocity of the telluric lines is constant down to a level of
approx. +/- 10 m/s (or 7/1000 of one pixel). Utilising the same telluriclines
as a rest frame for our radial velocity measurements of the science target, we
obtain a constant RV with a precision of approx. +/- 20 m/s for MS Vel as
expected for a M-giant.Comment: 12 pages, 6 figures, accepted by A&
A Dual-phase Xenon TPC for Scintillation and Ionisation Yield Measurements in Liquid Xenon
A small-scale, two-phase (liquid/gas) xenon time projection chamber (Xurich
II) was designed, constructed and is under operation at the University of
Zurich. Its main purpose is to investigate the microphysics of particle
interactions in liquid xenon at energies below 50 keV, which are relevant for
rare event searches using xenon as target material. Here we describe in detail
the detector, its associated infrastructure, and the signal identification
algorithm developed for processing and analysing the data. We present the first
characterisation of the new instrument with calibration data from an internal
83m-Kr source. The zero-field light yield is 15.0 and 14.0 photoelectrons/keV
at 9.4 keV and 32.1 keV, respectively, and the corresponding values at an
electron drift field of 1 kV/cm are 10.8 and 7.9 photoelectrons/keV. The charge
yields at these energies are 28 and 31 electrons/keV, with the proportional
scintillation yield of 24 photoelectrons per one electron extracted into the
gas phase, and an electron lifetime of 200 s. The relative energy
resolution, , is 11.9 % and 5.8 % at 9.4 keV and 32.1 keV,
respectively using a linear combination of the scintillation and ionisation
signals. We conclude with measurements of the electron drift velocity at
various electric fields, and compare these to literature values.Comment: 11 pages, 14 figure
The Energy Spectra and Relative Abundances of Electrons and Positrons in the Galactic Cosmic Radiation
Observations of cosmic-ray electrons and positrons have been made with a new
balloon-borne detector, HEAT (the "High-Energy Antimatter Telescope"), first
flown in 1994 May from Fort Sumner, NM. We describe the instrumental approach
and the data analysis procedures, and we present results from this flight. The
measurement has provided a new determination of the individual energy spectra
of electrons and positrons from 5 GeV to about 50 GeV, and of the combined
"all-electron" intensity (e+ + e-) up to about 100 GeV. The single power-law
spectral indices for electrons and positrons are alpha = 3.09 +/- 0.08 and 3.3
+/- 0.2, respectively. We find that a contribution from primary sources to the
positron intensity in this energy region, if it exists, must be quite small.Comment: latex2e file, 30 pages, 15 figures, aas2pp4.sty and epsf.tex needed.
To appear in May 10, 1998 issue of Ap.
Pattern Recognition and Event Reconstruction in Particle Physics Experiments
This report reviews methods of pattern recognition and event reconstruction
used in modern high energy physics experiments. After a brief introduction into
general concepts of particle detectors and statistical evaluation, different
approaches in global and local methods of track pattern recognition are
reviewed with their typical strengths and shortcomings. The emphasis is then
moved to methods which estimate the particle properties from the signals which
pattern recognition has associated. Finally, the global reconstruction of the
event is briefly addressed.Comment: 101 pages, 58 figure
Optical techniques for 3D surface reconstruction in computer-assisted laparoscopic surgery
One of the main challenges for computer-assisted surgery (CAS) is to determine the intra-opera- tive morphology and motion of soft-tissues. This information is prerequisite to the registration of multi-modal patient-specific data for enhancing the surgeon’s navigation capabilites by observ- ing beyond exposed tissue surfaces and for providing intelligent control of robotic-assisted in- struments. In minimally invasive surgery (MIS), optical techniques are an increasingly attractive approach for in vivo 3D reconstruction of the soft-tissue surface geometry. This paper reviews the state-of-the-art methods for optical intra-operative 3D reconstruction in laparoscopic surgery and discusses the technical challenges and future perspectives towards clinical translation. With the recent paradigm shift of surgical practice towards MIS and new developments in 3D opti- cal imaging, this is a timely discussion about technologies that could facilitate complex CAS procedures in dynamic and deformable anatomical regions
Energy dependence of exclusive photoproduction off protons in ultra-peripheral p-Pb collisions at = 5.02 TeV
The ALICE Collaboration has measured the energy dependence of exclusive
photoproduction of vector mesons off proton targets in
ultra-peripheral p-Pb collisions at a centre-of-mass energy per nucleon pair
TeV. The ee and decay channels
are used to measure the cross section as a function of the rapidity of the
in the range , corresponding to an energy in the
p centre-of-mass in the interval GeV.
The measurements, which are consistent with a power law dependence of the
exclusive photoproduction cross section, are compared to previous
results from HERA and the LHC and to several theoretical models. They are found
to be compatible with previous measurements.Comment: 25 pages, 3 captioned figures, 3 tables, authors from page 19,
published version, figures at http://alice-publications.web.cern.ch/node/455
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