2,597 research outputs found
Solar Neutrino Results from the Sudbury Neutrino Observatory
We describe here the measurement of the flux of neutrinos created by the
decay of solar ^8B by the Sudbury Neutrino Observatory (SNO). The neutrinos
were detected via the charged current (CC) reaction on deuterium and by the
elastic scattering (ES) of electrons. The CC reaction is sensitive exclusively
to 's, while the ES reaction also has a small sensitivity to
's and 's.
The flux of 's from ^8B decay measured by the CC reaction rate is
. Assuming no flavor transformation, the flux
inferred from the ES reaction rate is .
Comparison of to the Super-Kamiokande Collaboration's
precision value of yields a difference, assuming
the systematic uncertainties are normally distributed, providing evidence that
there is a non-electron flavor active neutrino component in the solar flux. The
total flux of active ^8B neutrinos is thus determined to be , in close agreement with the predictions of solar
models.Comment: Talk given at the XX International Symposium on Lepton and Photon
Interactions at High Energie
Towards precision distances and 3D dust maps using broadband Period--Magnitude relations of RR Lyrae stars
We determine the period-magnitude relations of RR Lyrae stars in 13
photometric bandpasses from 0.4 to 12 {\mu}m using timeseries observations of
134 stars. The Bayesian formalism, extended from our previous work to include
the effects of line-of-sight dust extinction, allows for the simultaneous
inference of the posterior distribution of the mean absolute magnitude, slope
of the period-magnitude power-law, and intrinsic scatter about a perfect
power-law for each bandpass. In addition, the distance modulus and
line-of-sight dust extinction to each RR Lyrae star in the calibration sample
is determined, yielding a sample median fractional distance error of 0.66%. The
intrinsic scatter in all bands appears to be larger than the photometric
errors, except in WISE W1 (3.4 {\mu}m) and W2 (4.6 {\mu}m) where the
photometric error ( mag) is to be comparable or larger
than the intrinsic scatter. Additional observations at these wavelengths could
improve the inferred distances to these sources further. As an application of
the methodology, we infer the distance to the RRc-type star RZCep at low
Galactic latitude () to be mag
( pc) with colour excess mag. This
distance, equivalent to a parallax of microarcsec, is consistent
with the published HST parallax measurement but with an uncertainty that is 13
times smaller than the HST measurement. If our measurements (and methodology)
hold up to scrutiny, the distances to these stars have been determined to an
accuracy comparable to those expected with Gaia. As RR Lyrae are one of the
primary components of the cosmic distance ladder, the achievement of sub-1%
distance errors within a formalism that accounts for dust extinction may be
considered a strong buttressing of the path to eventual 1% uncertainties in
Hubble's constant.Comment: 21 pages, 29 figures, 2 tables, abstract abridged for arXiv. Comments
solicited on referee report (received June 9, 2014) linked:
https://gist.github.com/profjsb/c6c4e2f3a20ea02f1762 . Public archive of code
used to generate results and figures:
https://github.com/ckleinastro/period_luminosity_relation_fittin
Prototype Detector for Ultrahigh Energy Neutrino Detection
Necessary technical experience is being gained from successful construction
and deployment of current prototype detectors to search for UHE neutrinos in
Antarctica, Lake Baikal in Russia, and the Mediterranean. The prototype
detectors have also the important central purpose of determining whether or not
UHE neutrinos do in fact exist in nature by observation of at least a few UHE
neutrino-induced leptons with properties that are not consistent with expected
backgrounds. We discuss here the criteria for a prototype detector to
accomplish that purpose in a convincing way even if the UHE neutrino flux is
substantially lower than predicted at present.Comment: 18 pages, 8 figures, submitted to Astroparticle Physic
Probing the distance and morphology of the Large Magellanic Cloud with RR Lyrae stars
We present a Bayesian analysis of the distances to 15,040 Large Magellanic
Cloud (LMC) RR Lyrae stars using - and -band light curves from the
Optical Gravitational Lensing Experiment, in combination with new -band
observations from the Dark Energy Camera. Our median individual RR Lyrae
distance statistical error is 1.89 kpc (fractional distance error of 3.76 per
cent). We present three-dimensional contour plots of the number density of LMC
RR Lyrae stars and measure a distance to the core LMC RR Lyrae centre of
,
equivalently . This finding is statistically consistent with and four
times more precise than the canonical value determined by a recent
meta-analysis of 233 separate LMC distance determinations. We also measure a
maximum tilt angle of at a position angle of
, and report highly precise constraints on the , , and RR
Lyrae period--magnitude relations. The full dataset of observed mean-flux
magnitudes, derived colour excess values, and fitted distances for
the 15,040 RR Lyrae stars produced through this work is made available through
the publication's associated online data.Comment: 7 pages, 8 figure
Final Technical Report
Over the past year, our group here at the University of Texas has continued to focus primarily on analysis of data from the Sudbury Neutrino Observatory (SNO), in particular on a push to lower the energy threshold used in solar neutrino analyses and on a search for short time-scale astrophysical phenomena in the neutrino data set. We have in addition begun R and D and simulation work on a new direct search for dark matter as part of the DEAP/CLEAN collaboration, as well as an effort associated with work on a new experiment using the existing SNO detector (SNO+). Lastly, we have also been doing some very early studies of an experiment to measure the neutrino mass using the beta decay of cold tritium atoms. Our work on SNO has focused primarily on making a low-threshold spectral measurement of the flux of {sup 8}B solar neutrinos. The work forms the bulk of graduate student Stan Seibert's PhD thesis. Nearly all systematic uncertainties associated with the analysis have now been measured, in particular the dominant uncertainties such as energy scale and resolution, and the uncertainty on SNO's 'isotropy' parameter used to distinguish electrons, neutrons, and radioactive backgrounds. It is now clear that we will be able to fit the {sup 8}B energy spectrum to a threshold of 4 MeV or below, with uncertainties in the 4 MeV bin somewhere between 15-20%. This will be the lowest threshold measurement ever made using the water Cherenkov technique, and will provide a test of the MSW-predicted distortion of the {sup 8}B energy spectrum. As an additional benefit of the low threshold analysis, we expect to get total uncertainties on the NC flux in the neighborhood of 4%, nearly a factor of 2 better than any of SNO's previous measurements of the total {sup 8}B flux
K-12 School Shootings in Context: New Findings from The American School Shooting Study (TASSS)
The American School Shooting Study (TASSS) is an ongoing mixed-method project funded by the National Institute of Justice to catalog US school shootings. It has amassed data based on open sources and other public materials dating back to 1990. This brief presents new insights from TASSS, diving deeper into the database's potential to examine the locations, timing, and student involvement of youth-perpetrated gun violence
American jihadi terrorism: A comparison of homicides and unsuccessful plots
While the number of American jihadi terrorist attacks remains relatively rare, terrorist plots thwarted by law enforcement have increased since September 11, 2001. Although these law enforcement blocks of would-be terrorists are considered counterterrorism triumphs by the FBI, human rights and civil liberty watch groups have conversely suggested that those who plan for attacks alongside government informants and undercover agents may be unique and essentially dissimilar from terrorists. Underlying this debate is the empirical question of how planned yet unsuccessful attacks and their plotters compare to successful terrorist homicides and their perpetrators. The current study addresses this question by comparatively examining jihadi terrorist homicides and unsuccessful plots occurring in part or wholly on U.S. soil between 1990 and 2014. Data for this study come from the U.S. Extremist Crime Database (ECDB), an open-source database with information on terrorism and extremist crimes. Based on these data, descriptive statistics are provided for several incident, offender, and target variables across three jihadi terrorist violence categories, including homicides, plots with specified targets, and plots with non-specific targets. We find several important differences across categories of terrorist violence, suggesting that unsuccessful plotters and their intended crimes vary from their more successful terrorist counterparts
A Bayesian Approach to Calibrating Period-Luminosity Relations of RR Lyrae Stars in the Mid-Infrared
A Bayesian approach to calibrating period-luminosity (PL) relations has
substantial benefits over generic least-squares fits. In particular, the
Bayesian approach takes into account the full prior distribution of the model
parameters, such as the a priori distances, and refits these parameters as part
of the process of settling on the most highly-constrained final fit.
Additionally, the Bayesian approach can naturally ingest data from multiple
wavebands and simultaneously fit the parameters of PL relations for each
waveband in a procedure that constrains the parameter posterior distributions
so as to minimize the scatter of the final fits appropriately in all wavebands.
Here we describe the generalized approach to Bayesian model fitting and then
specialize to a detailed description of applying Bayesian linear model fitting
to the mid-infrared PL relations of RR Lyrae variable stars. For this example
application we quantify the improvement afforded by using a Bayesian model fit.
We also compare distances previously predicted in our example application to
recently published parallax distances measured with the Hubble Space Telescope
and find their agreement to be a vindication of our methodology. Our intent
with this article is to spread awareness of the benefits and applicability of
this Bayesian approach and encourage future PL relation investigations to
consider employing this powerful analysis method.Comment: 6 pages, 1 figure. Accepted for publication in Astrophysics & Space
Science. Following a presentation at the conference The Fundamental Cosmic
Distance Scale: State of the Art and the Gaia Perspective, Naples, May 201
Mid-infrared Period-Luminosity Relations of RR Lyrae Stars Derived from the WISE Preliminary Data Release
Interstellar dust presents a significant challenge to extending
parallax-determined distances of optically observed pulsational variables to
larger volumes. Distance ladder work at mid-infrared wavebands, where dust
effects are negligible and metallicity correlations are minimized, have been
largely focused on few-epoch Cepheid studies. Here we present the first
determination of mid-infrared period-luminosity (PL) relations of RR Lyrae
stars from phase-resolved imaging using the preliminary data release of the
Wide-Field Infrared Survey Explorer (WISE). We present a novel statistical
framework to predict posterior distances of 76 well-observed RR Lyrae that uses
the optically constructed prior distance moduli while simultaneously imposing a
power-law PL relation to WISE-determined mean magnitudes. We find that the
absolute magnitude in the bluest WISE filter is M_W1 = (-0.421+-0.014) -
(1.681+-0.147)*log(P/0.50118 day), with no evidence for a correlation with
metallicity. Combining the results from the three bluest WISE filters, we find
that a typical star in our sample has a distance measurement uncertainty of
0.97% (statistical) plus 1.17% (systematic). We do not fundamentalize the
periods of RRc stars to improve their fit to the relations. Taking the
Hipparcos-derived mean V-band magnitudes, we use the distance posteriors to
determine a new optical metallicity-luminosity relation which we present in
Section 5. The results of this analysis will soon be tested by HST parallax
measurements and, eventually, with the Gaia astrometric mission.Comment: 33 pages, 12 figures, 2 tables. Accepted for publication in ApJ, June
27th, 201
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