457,183 research outputs found
The Generalized Centroid Difference method for lifetime measurements via gamma-gamma coincidences using large fast-timing arrays.
A novel method for direct electronic "fast-timing" lifetime measurements of nuclear excited states via gamma-gamma coincidences using an array equipped with N very fast high-resolution LaBr3(Ce) scintillator detectors is presented. The generalized centroid difference method provides two independent "start" and "stop" time spectra obtained without any correction by a superposition of the N(N - 1)/2 calibrated gamma-gamma time difference spectra of the N detector fast-timing system. The two fast-timing array time spectra correspond to a forward and reverse gating of a specific gamma-gamma cascade and the centroid difference as the time shift between the centroids of the two time spectra provides a picosecond-sensitive mirror-symmetric observable of the set-up. The energy-dependent mean prompt response difference between the start and stop events is calibrated and used as a single correction for lifetime determination. These combined fast-timing array mean gamma-gamma zero-time responses can be determined for 40 keV < E-gamma < 1.4 MeV with a precision better than 10 ps using a Eu-152 gamma-ray source. The new method is described with examples of (n,gamma) and (n,f,gamma) experiments performed at the intense cold-neutron beam facility PF1B of the Institut Laue-Langevin in Grenoble, France, using 16 LaBr3(Ce) detectors within the EXILL&FATIMA campaign in 2013. The results are discussed with respect to possible systematic errors induced by background contributions
Kolmogorov-Smirnov method for the determination of signal time-shifts
A new method for the determination of electric signal time-shifts is
introduced. As the Kolmogorov-Smirnov test, it is based on the comparison of
the cumulative distribution functions of the reference signal with the test
signal. This method is very fast and thus well suited for on-line applications.
It is robust to noise and its performances in terms of precision are excellent
for time-shifts ranging from a fraction to several sample durations.
PACS. 29.40.Gx (Tracking and position-sensitive detectors), 29.30.Kv (X- and
-ray spectroscopy), 07.50.Qx (Signal processing electronics)Comment: 8 pages, 7 figure
Investigation of top mass measurements with the ATLAS detector at LHC
Several methods for the determination of the mass of the top quark with the
ATLAS detector at the LHC are presented. All dominant decay channels of the top
quark can be explored. The measurements are in most cases dominated by
systematic uncertainties. New methods have been developed to control those
related to the detector. The results indicate that a total error on the top
mass at the level of 1 GeV should be achievable.Comment: 47 pages, 40 figure
2S hyperfine structure of atomic deuterium
We have measured the frequency splitting between the and hyperfine sublevels in atomic deuterium by an optical differential
method based on two-photon Doppler-free spectroscopy on a cold atomic beam. The
result Hz is the most precise value for
this interval to date. In comparison to the previous radio-frequency
measurement we have improved the accuracy by the factor of three.
The specific combination of hyperfine frequency intervals for metastable- and
ground states in deuterium atom derived from our measurement is in a good agreement with
calculated from quantum-electrodynamics theory.Comment: 7 pages, 7 figure
Finding critical points using improved scaling Ansaetze
Analyzing in detail the first corrections to the scaling hypothesis, we
develop accelerated methods for the determination of critical points from
finite size data. The output of these procedures are sequences of
pseudo-critical points which rapidly converge towards the true critical points.
In fact more rapidly than previously existing methods like the Phenomenological
Renormalization Group approach. Our methods are valid in any spatial
dimensionality and both for quantum or classical statistical systems. Having at
disposal fast converging sequences, allows to draw conclusions on the basis of
shorter system sizes, and can be extremely important in particularly hard cases
like two-dimensional quantum systems with frustrations or when the sign problem
occurs. We test the effectiveness of our methods both analytically on the basis
of the one-dimensional XY model, and numerically at phase transitions occurring
in non integrable spin models. In particular, we show how a new Homogeneity
Condition Method is able to locate the onset of the
Berezinskii-Kosterlitz-Thouless transition making only use of ground-state
quantities on relatively small systems.Comment: 16 pages, 4 figures. New version including more general Ansaetze
basically applicable to all case
The Potential-Density Phase Shift Method for Determining the Corotation Radii in Spiral and Barred Galaxies
We have developed a new method for determining the corotation radii of
density waves in disk galaxies, which makes use of the radial distribution of
an azimuthal phase shift between the potential and density wave patterns. The
approach originated from improved theoretical understandings of the relation
between the morphology and kinematics of galaxies, and on the dynamical
interaction between density waves and the basic-state disk stars which results
in the secular evolution of disk galaxies. In this paper, we present the
rationales behind the method, and the first application of it to several
representative barred and grand-design spiral galaxies, using near-infrared
images to trace the mass distributions, as well as to calculate the potential
distributions used in the phase shift calculations. We compare our results with
those from other existing methods for locating the corotations, and show that
the new method both confirms the previously-established trends of bar-length
dependence on galaxy morphological types, as well as provides new insights into
the possible extent of bars in disk galaxies. Application of the method to a
larger sample and the preliminary analysis of which show that the phase shift
method is likely to be a generally-applicable, accurate, and essentially
model-independent method for determining the pattern speeds and corotation
radii of single or nested density wave patterns in galaxies. Other implications
of this work are: most of the nearby bright disk galaxies appear to possess
quasi-stationary spiral modes; that these density wave modes and the associated
basic state of the galactic disk slowly transform over time; and that
self-consistent N-particle systems contain physics not revealed by the passive
orbit analysis approaches.Comment: 48 pages, 16 figures. Accepted for publication in the Astronomical
Journa
High Precision Astrometric Millimeter VLBI Using a New Method for Atmospheric Calibration
We describe a new method which achieves high precision Very Long Baseline
Interferometry (VLBI) astrometry in observations at millimeter wavelengths. It
combines fast frequency-switching observations, to correct for the dominant
non-dispersive tropospheric fluctuations, with slow source-switching
observations, for the remaining ionospheric dispersive terms. We call this
method Source-Frequency Phase Referencing. Provided that the switching cycles
match the properties of the propagation media, one can recover the source
astrometry. We present an analytic description of the two-step calibration
strategy, along with an error analysis to characterize its performance. Also,
we provide observational demonstrations of a successful application with
observations using the Very Long Baseline Array at 86 GHz of the pairs of
sources 3C274 & 3C273 and 1308+326 & 1308+328, under various conditions. We
conclude that this method is widely applicable to millimeter VLBI observations
of many target sources, and unique in providing bona-fide astrometrically
registered images and high precision relative astrometric measurements in
mm-VLBI using existing and newly built instruments.Comment: Astronomical Journal, accepted for publicatio
Hydrogen Spectroscopy with a Lamb-shift Polarimeter - An Alternative Approach Towards Anti-Hydrogen Spectroscopy Experiments
A Lamb-shift polarimeter, which has been built for a fast determination of
the polarization of protons and deuterons of an atomic-beam source and which is
frequently used in the ANKE experiment at COSY-J\"ulich, is shown to be an
excellent device for atomic-spectroscopy measurements of metastable hydrogen
isotopes. It is demonstrated that magnetic and electric dipole transitions in
hydrogen can be measured as a function of the external magnetic field, giving
access to the full Breit-Rabi diagram for the and the
states. This will allow the study of hyperfine structure, factors and the
classical Lamb shift. Although the data are not yet competitive with
state-of-the-art measurements, the potential of the method is enormous,
including a possible application to anti-hydrogen spectroscopy.Comment: 6 pages, 7 figures, accepted by European Physical Journal
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