1,768 research outputs found
Regression calibration for Cox regression under heteroscedastic measurement error - Determining risk factors of cardiovascular diseases from error-prone nutritional replication data
For instance nutritional data are often subject to severe measurement error, and an adequate adjustment of the estimators is indispensable to avoid deceptive conclusions. This paper discusses and extends the method of regression calibration to correct for measurement error in Cox regression. Special attention is paid to the modelling of quadratic predictors, the role of heteroscedastic measurement error, and the efficient use of replicated measurements of the surrogates. The method is used to analyze data from the German part of the MONICA cohort study on cardiovascular diseases. The results corroborate the importance of taking into account measurement error carefully
The impact of photoproduction on the resonance spectrum
The J\"ulich-Bonn coupled-channel framework is extended to
photoproduction. The spectrum of nucleon and resonances is extracted
from simultaneous fits to several pion-induced reactions in addition to pion,
eta and photoproduction off the proton. More than 40,000 data
points up to a center-of-mass energy of E2.3 GeV including recently
measured double-polarization observables are analyzed. The influence of the
channel on the extracted resonance parameters and the
appearance of states not seen in other channels is investigated. The
J\"ulich-Bonn model includes effective three-body channels and guarantees
unitarity and analyticity, which is a prerequisite for a reliable determination
of the resonance spectrum in terms of poles and residues.Comment: 21 pages, 11 figures. Minor modifications, additional information in
the appendix. Accepted for publication in Eur. Phys. J.
Correlations of Partial Waves for Multi-Reaction Analyses
In the search for missing baryonic resonances, many analyses include data
from a variety of pion- and photon-induced reactions. For elastic
scattering, however, usually the partial waves of the SAID or other groups are
fitted, instead of data. We provide the partial-wave covariance matrices needed
to perform correlated fits, in which the obtained equals the
actual up non-linear and normalization corrections. For any analysis
relying on partial waves extracted from elastic pion scattering, this is a
prerequisite to assess the significance of resonance signals and to assign any
uncertainty on results. The influence of systematic errors is also considered.Comment: 7 pages, 3 figures; Acknowledgements update
Kaon Photoproduction and the Decay Parameter
The weak decay parameter of the is an important quantity
for the extraction of polarization observables in various experiments.
Moreover, in combination with from decay it provides a
measure for matter-antimatter asymmetry. The weak decay parameter also affects
the decay parameters of the and baryons and, in general, any
quantity in which the polarization of the is relevant. The recently
reported value by the BESIII collaboration of is significantly
larger than the previous PDG value of that had been accepted and
used for over 40 years. In this work we make an independent estimate of
, using an extensive set of polarization data measured in kaon
photoproduction in the baryon resonance region and constraints set by spin
algebra. The obtained value is 0.721(6)(5). The result is corroborated by
multiple statistical tests as well as a modern phenomenological model, showing
that our new value yields the best description of the data in question. Our
analysis supports the new BESIII finding that is significantly
larger than the previous PDG value. Any experimental quantity relying on the
value of should therefore be re-considered.Comment: 6 pages, 1 figure
Helicity Amplitudes of the Lambda(1670) and two Lambda(1405) as dynamically generated resonances
We determine the helicity amplitudes A_1/2 and radiative decay widths in the
transition Lambda(1670) to gamma Y (Y=Lambda or Sigma^0). The Lambda(1670) is
treated as a dynamically generated resonance in meson-baryon chiral dynamics.
We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 3
\pm 2 keV and to gamma Sigma^0 as 120 \pm 50 keV. Also, the Q^2 dependence of
the helicity amplitudes A_1/2 is calculated. We find that the K Xi component in
the Lambda(1670) structure, mainly responsible for the dynamical generation of
this resonance, is also responsible for the significant suppression of the
decay ratio Gamma_{gamma Lambda}/Gamma_{gamma Sigma^0}. A measurement of the
ratio would, thus, provide direct access to the nature of the Lambda(1670). To
compare the result for the Lambda(1670), we calculate the helicity amplitudes
A_1/2 for the two states of the Lambda(1405). Also, the analytic continuation
of Feynman parameterized integrals of more complicated loop amplitudes to the
complex plane is developed which allows for an internally consistent evaluation
of A_1/2.Comment: 15 pages, 8 figure
Ramsey interferometry with an atom laser
We present results on a free-space atom interferometer operating on the first
order magnetically insensitive |F=1,mF=0> -> |F=2,mF=0> transition of
Bose-condensed 87Rb atoms. A pulsed atom laser is output-coupled from a
Bose-Einstein condensate and propagates through a sequence of two internal
state beam splitters, realized via coherent Raman transitions between the two
interfering states. We observe Ramsey fringes with a visibility close to 100%
and determine the current and the potentially achievable interferometric phase
sensitivity. This system is well suited to testing recent proposals for
generating and detecting squeezed atomic states.Comment: published version, 8 pages, 3 figure
Inertia and chiral edge modes of a skyrmion magnetic bubble
The dynamics of a vortex in a thin-film ferromagnet resembles the motion of a
charged massless particle in a uniform magnetic field. Similar dynamics is
expected for other magnetic textures with a nonzero skyrmion number. However,
recent numerical simulations revealed that skyrmion magnetic bubbles show
significant deviations from this model. We show that a skyrmion bubble
possesses inertia and derive its mass from the standard theory of a thin-film
ferromagnet. Besides center-of-mass motion, other low energy modes are waves on
the edge of the bubble traveling with different speeds in opposite directions.Comment: updated simulation detail
Pulsed pumping of a Bose-Einstein condensate
In this work, we examine a system for coherent transfer of atoms into a
Bose-Einstein condensate. We utilize two spatially separate Bose-Einstein
condensates in different hyperfine ground states held in the same dc magnetic
trap. By means of a pulsed transfer of atoms, we are able to show a clear
resonance in the timing of the transfer, both in temperature and number, from
which we draw conclusions about the underlying physical process. The results
are discussed in the context of the recently demonstrated pumped atom laser.Comment: 5 pages, 5 figures, published in Physical Review
Physics Opportunities with Meson Beams
Over the past two decades, meson photo- and electro-production data of
unprecedented quality and quantity have been measured at electromagnetic
facilities worldwide. By contrast, the meson-beam data for the same hadronic
final states are mostly outdated and largely of poor quality, or even
nonexistent, and thus provide inadequate input to help interpret, analyze, and
exploit the full potential of the new electromagnetic data. To reap the full
benefit of the high-precision electromagnetic data, new high-statistics data
from measurements with meson beams, with good angle and energy coverage for a
wide range of reactions, are critically needed to advance our knowledge in
baryon and meson spectroscopy and other related areas of hadron physics. To
address this situation, a state of-the-art meson-beam facility needs to be
constructed. The present paper summarizes unresolved issues in hadron physics
and outlines the vast opportunities and advances that only become possible with
such a facility.Comment: 46 pages, 10 figures, 4 table
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