3,814 research outputs found
Information Content of Polarization Measurements
Information entropy is applied to the state of knowledge of reaction
amplitudes in pseudoscalar meson photoproduction, and a scheme is developed
that quantifies the information content of a measured set of polarization
observables. It is shown that this definition of information is a more
practical measure of the quality of a set of measured observables than whether
the combination is a mathematically complete set. It is also shown that when
experimental uncertainty is introduced, complete sets of measurements do not
necessarily remove ambiguities, and that experiments should strive to measure
as many observables as practical in order to extract amplitudes.Comment: 19 pages, 4 figures; figures updated, minor textual correction
Bayesian model selection for electromagnetic kaon production on the nucleon
We present the results of a Bayesian analysis of a Regge model to describe
the background contribution for K+ Lambda and K+ Sigma0 photoproduction. The
model is based on the exchange of K+(494) and K*+(892) trajectories in the
t-channel. We utilise the Bayesian evidence Z to determine the best model
variant for each channel. The Bayesian evidence integrals were calculated using
the Nested Sampling algorithm. For different prior widths, we find decisive
Bayesian evidence (\Delta ln Z ~ 24) for a K+ Lambda photoproduction Regge
model with a positive vector coupling and a negative tensor coupling constant
for the K*+(892) trajectory, and a rotating phase factor for both trajectories.
Using the chi^2 minimisation method, one could not draw this conclusion from
the same dataset. For the K+ Sigma0 photoproduction Regge model, on the other
hand, the difference between the evidence integrals is insufficient to pinpoint
one model variant.Comment: 13 pages, 4 figure
Electromagnetic KY production from the proton in a Regge-plus-resonance approach
A Regge-plus-resonance (RPR) description of the p(\gamma,K)Y and p(e,e'K)Y
processes (Y = \Lambda, \Sigma^{0,+}) is presented. The proposed reaction
amplitude consists of Regge-trajectory exchanges in the t channel, supplemented
with a limited selection of s-channel resonance diagrams. The RPR framework
contains a considerably smaller number of free parameters than a typical
effective-Lagrangian model. Nevertheless, it provides an acceptable overall
description of the photo- and electroproduction observables over an extensive
photon energy range. It is shown that the electroproduction response functions
and polarization observables are particularly useful for fine-tuning both the
background and resonance parameters.Comment: 4 pages, 3 figures, Proceedings for IX International Conference on
Hypernuclear and Strange Particle Physics (HYP2006), October 10-14 2006,
Main
Differential cross section analysis in kaon photoproduction using associated legendre polynomials
Angular distributions of differential cross sections from the latest CLAS
data sets \cite{bradford}, for the reaction have been analyzed using associated Legendre polynomials. This
analysis is based upon theoretical calculations in Ref. \cite{fasano} where all
sixteen observables in kaon photoproduction can be classified into four
Legendre classes. Each observable can be described by an expansion of
associated Legendre polynomial functions. One of the questions to be addressed
is how many associated Legendre polynomials are required to describe the data.
In this preliminary analysis, we used data models with different numbers of
associated Legendre polynomials. We then compared these models by calculating
posterior probabilities of the models. We found that the CLAS data set needs no
more than four associated Legendre polynomials to describe the differential
cross section data. In addition, we also show the extracted coefficients of the
best model.Comment: Talk given at APFB08, Depok, Indonesia, August, 19-23, 200
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Cathodoluminescence studies of phosphors in a scanning electron microscope
Cathodoluminescence studies are reported of phosphors in a field emission scanning electron microscope (FESEM). A number of phosphor materials have been studied and exhibited a pronounced comet-like structure at high scan rates, because the particle continued to emit light after the beam had moved onto subsequent pixels. Image analysis has been used to study the loss of brightness along the tail and hence to determine the decay time of the materials. This technique provides a simple and convenient way to study the decay times of individual particles
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
Bayesian Analysis of Pentaquark Signals from CLAS Data
We examine the results of two measurements by the CLAS collaboration, one of which claimed evidence for a Θ+ pentaquark, while the other found no such evidence. The unique feature of these two experiments was that they were performed with the same experimental setup. Using a Bayesian analysis, we find that the results of the two experiments are in fact compatible with each other, but that the first measurement did not contain sufficient information to determine unambiguously the existence of a Θ+. Further, we suggest a means by which the existence of a new candidate particle can be tested in a rigorous manner
Racial and Ethnic Disparities in Contraceptive Use in Young Women
Background: Young women have the highest rates of unintended pregnancies among reproductive aged women. Black and Latina women are at highest risk. Few studies have examined reasons for these differences. In this study, we examined disparities in contraceptive use and contraceptive counseling by race and ethnicity among young women.
Methods: Using the 2011-2013 National Survey of Family Growth (NSFG), a cross-sectional, nationally representative database, our analysis included women aged 15-24 years who had sexual intercourse within the past year, and were not pregnant or seeking pregnancy. The primary outcomes were contraceptive use and receipt of contraceptive services within the past 12 months.
Results: Young women who identify as Hispanic (H) or Non-Hispanic Black (NHB) are less likely to report current contraceptive use than their non-Hispanic White (NHW) or Non-Hispanic Other (NHO) counterparts. This finding remains statistically significant among NHB women after controlling for confounders (H: adjusted OR=0.57±0.17, 95% CI [0.32, 1.02]; NHB: adjusted OR=0.51±0.13, 95% CI [0.31-0.82;] NHO: OR=1.91±0.67, 95% CI [0.96, 3.81]). There were no differences in birth control counseling received by race/ethnicity. However, NHW and NHO were more likely to have been issued contraception within the last 12 months (H: 49.6%, NHB: 49.0%, NHW: 60.1%, NHO: 64.8; p=0.047).
Conclusions/Implications: Young Black and Latina women are less likely to use contraception than other racial and ethnic groups; this difference persists among young black women after controlling for sociodemographic differences. Future studies should explore reasons for the decreased contraceptive usage rate among young black women
Optical Interferometry of early-type stars with PAVO@CHARA. I. Fundamental stellar properties
We present interferometric observations of 7 main-sequence and 3 giant stars
with spectral types from B2 to F6 using the PAVO beam combiner at the CHARA
array. We have directly determined the angular diameters for these objects with
an average precision of 2.3%. We have also computed bolometric fluxes using
available photometry in the visible and infrared wavelengths, as well as
space-based ultraviolet spectroscopy. Combined with precise \textit{Hipparcos}
parallaxes, we have derived a set of fundamental stellar properties including
linear radius, luminosity and effective temperature. Fitting the latter to
computed isochrone models, we have inferred masses and ages of the stars. The
effective temperatures obtained are in good agreement (at a 3% level) with
nearly-independent temperature estimations from spectroscopy. They validate
recent sixth-order polynomial (B-V)- empirical relations
\citep{Boyajian2012a}, but suggest that a more conservative third-order
solution \citep{vanBelle2009} could adequately describe the
(V-K)- relation for main-sequence stars of spectral type A0 and
later. Finally, we have compared mass values obtained combining surface gravity
with inferred stellar radius (\textit{gravity mass}) and as a result of the
comparison of computed luminosity and temperature values with stellar
evolutionary models (\textit{isochrone mass}). The strong discrepancy between
isochrone and gravity mass obtained for one of the observed stars,
\,Lyr, suggests that determination of the stellar atmosphere parameters
should be revised.Comment: 13 pages, 9 figures, accepted for publication in MNRA
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