574 research outputs found
Search for antiproton decay at the Fermilab Antiproton Accumulator
A search for antiproton decay has been made at the Fermilab Antiproton
Accumulator. Limits are placed on thirteen antiproton decay modes. The results
include the first explicit experimental limits on the muonic decay modes of the
antiproton, and the first limits on the decay modes e- gamma gamma, and e-
omega. The most stringent limit is for the decay mode pbar-> e- gamma. At 90%
C.L. we find that tau/B(pbar-> e- gamma) > 7 x 10^5 yr. The most stringent
limit for decay modes with a muon in the final state is for the decay pbar->
mu- gamma. At 90% C.L. we find that tau/B(pbar-> mu- gamma) > 5 x 10^4 yr.Comment: 20 pages, 8 figures. Submitted to Phys. Rev. D. Final results on 13
channels (was 15) are presente
Search for muonic decays of the antiproton at the Fermilab Antiproton Accumulator
A search for antiproton decay has been made at the Fermilab Antiproton
Accumulator. Limits are placed on six antiproton decay modes which contain a
final-state muon. At the 90% C.L. we find that
tau/B(mu gamma) > 5.0 x 10^4 yr,
tau/B(mu pi0) > 4.8 x 10^4 yr,
tau/B(mu eta) > 7.9 x 10^3 yr,
tau/B(mu gamma gamma) > 2.3 x 10^4 yr,
tau/B(mu K0S > 4.3 x 10^3 yr, and
tau/B(mu K0L) > 6.5 x 10^3 yr.Comment: 8 pages + 3 Postscript figure
Supernova Simulations and Strategies For the Dark Energy Survey
We present an analysis of supernova light curves simulated for the upcoming
Dark Energy Survey (DES) supernova search. The simulations employ a code suite
that generates and fits realistic light curves in order to obtain distance
modulus/redshift pairs that are passed to a cosmology fitter. We investigated
several different survey strategies including field selection, supernova
selection biases, and photometric redshift measurements. Using the results of
this study, we chose a 30 square degree search area in the griz filter set. We
forecast 1) that this survey will provide a homogeneous sample of up to 4000
Type Ia supernovae in the redshift range 0.05<z<1.2, and 2) that the increased
red efficiency of the DES camera will significantly improve high-redshift color
measurements. The redshift of each supernova with an identified host galaxy
will be obtained from spectroscopic observations of the host. A supernova
spectrum will be obtained for a subset of the sample, which will be utilized
for control studies. In addition, we have investigated the use of combined
photometric redshifts taking into account data from both the host and
supernova. We have investigated and estimated the likely contamination from
core-collapse supernovae based on photometric identification, and have found
that a Type Ia supernova sample purity of up to 98% is obtainable given
specific assumptions. Furthermore, we present systematic uncertainties due to
sample purity, photometric calibration, dust extinction priors, filter-centroid
shifts, and inter-calibration. We conclude by estimating the uncertainty on the
cosmological parameters that will be measured from the DES supernova data.Comment: 46 pages, 30 figures, resubmitted to ApJ as Revision 2 (final author
revision), which has subtle editorial differences compared to the published
paper (ApJ, 753, 152). Note that this posting includes PDF only due to a bug
in either the latex macros or the arXiv submission system. The source files
are available in the DES document database:
http://des-docdb.fnal.gov/cgi-bin/ShowDocument?docid=624
Type Ia Supernova Properties as a Function of the Distance to the Host Galaxy in the SDSS-II SN Survey
We use type-Ia supernovae (SNe Ia) discovered by the SDSS-II SN Survey to
search for dependencies between SN Ia properties and the projected distance to
the host galaxy center, using the distance as a proxy for local galaxy
properties (local star-formation rate, local metallicity, etc.). The sample
consists of almost 200 spectroscopically or photometrically confirmed SNe Ia at
redshifts below 0.25. The sample is split into two groups depending on the
morphology of the host galaxy. We fit light-curves using both MLCS2k2 and
SALT2, and determine color (AV, c) and light-curve shape (delta, x1) parameters
for each SN Ia, as well as its residual in the Hubble diagram. We then
correlate these parameters with both the physical and the normalized distances
to the center of the host galaxy and look for trends in the mean values and
scatters of these parameters with increasing distance. The most significant (at
the 4-sigma level) finding is that the average fitted AV from MLCS2k2 and c
from SALT2 decrease with the projected distance for SNe Ia in spiral galaxies.
We also find indications that SNe in elliptical galaxies tend to have narrower
light-curves if they explode at larger distances, although this may be due to
selection effects in our sample. We do not find strong correlations between the
residuals of the distance moduli with respect to the Hubble flow and the
galactocentric distances, which indicates a limited correlation between SN
magnitudes after standardization and local host metallicity.Comment: Accepted for publication in The Astrophysical Journal (33 pages, 5
figures, 8 tables
Properties of Type Ia supernovae inside rich galaxy clusters
We used the Gaussian Mixture Brightest Cluster Galaxy catalogue and Sloan Digital Sky
Survey-II supernovae data with redshifts measured by the Baryon Oscillation Spectroscopic
Survey to identify 48 Type Ia supernovae (SNe Ia) residing in rich galaxy clusters and compare
their properties with 1015 SNe Ia in the field. Their light curves were parametrized by the
SALT2 model and the significance of the observed differences was assessed by a resampling
technique. To test our samples and methods, we first looked for known differences between
SNe Ia residing in active and passive galaxies. We confirm that passive galaxies host SNe
Ia with smaller stretch, weaker colour–luminosity relation [β of 2.54(22) against 3.35(14)],
and that are ∼0.1 mag more luminous after stretch and colour corrections. We show that
only 0.02 per cent of random samples drawn from our set of SNe Ia in active galaxies can
reach these values. Reported differences in the Hubble residuals scatter could not be detected,
possibly due to the exclusion of outliers. We then show that, while most field and cluster
SNe Ia properties are compatible at the current level, their stretch distributions are different
(∼3σ): besides having a higher concentration of passive galaxies than the field, the cluster’s
passive galaxies host SNe Ia with an average stretch even smaller than those in field passive
galaxies (at 95 per cent confidence).We argue that the older age of passive galaxies in clusters
is responsible for this effect since, as we show, old passive galaxies host SNe Ia with smaller
stretch than young passive galaxies (∼4σ).Web of Scienc
The dark energy spectrometer - A potential multi-fiber instrument for the Blanco 4-meter telescope
We describe the preliminary design of the Dark Energy Spectrometer (DESpec), a fiber-fed spectroscopic instrument concept for the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory (CTIO). DESpec would take advantage of the infrastructure recently deployed for the Dark Energy Camera (DECam). DESpec would be mounted in the new DECam prime focus cage, would be interchangeable with DECam, would share the DECam optical corrector, and would feature a focal plane with ∼4000 robotically positioned optical fibers feeding multiple high-throughput spectrometers. The instrument would have a field of view of 3.8 square degrees, a wavelength range of approximately 500<λ<1000 nm, and a spectral resolution of R∼3000. DESpec would provide a powerful spectroscopic follow-up system for sources in the Southern hemisphere discovered by the Dark Energy Survey and LSST
NTT and NOT spectroscopy of SDSS-II supernovae
Context. The SDSS-II Supernova Survey, conducted between 2005 and 2007, was
designed to detect a large number of Type Ia supernovae (SNe Ia) around z~0.2,
the redshift "gap" between low-z and high-z SN searches. The survey has
provided multi-band photometric lightcurves for variable targets, and SN
candidates were scheduled for spectroscopic observations, primarily to provide
SN classification and accurate redshifts. We present SN spectra obtained in
2006 and 2007 using the NTT and the NOT. Aims. We provide an atlas of SN
spectra in the range z =0.03-0.32 that complements the well-sampled lightcurves
from SDSS-II in the forthcoming three-year SDSS SN cosmology analysis. The
sample can, for example, be used for spectral studies of SNe Ia, which are
critical for understanding potential systematic effects when SNe are used to
determine cosmological distances. Methods. The spectra were reduced in a
uniform manner, and special care was taken in estimating the uncertainties for
the different processing steps. Host-galaxy light was subtracted when possible
and the SN type fitted using the SuperNova IDentification code (SNID). We also
present comparisons between spectral and photometric dating using SALT
lightcurve fits to the photometry from SDSS-II, as well as the global
distribution of our sample in terms of the lightcurve parameters: stretch and
colour. Results. We report new spectroscopic data from 141 SNe Ia, mainly
between -9 and +15 days from lightcurve maximum, including a few cases of
multi-epoch observations. This homogeneous, host-galaxy subtracted, SN Ia
spectroscopic sample is among the largest such data sets and unique in its
redshift interval. The sample includes two potential SN 1991T-like SNe (SN
2006on and SN 2007ni) and one potential SN 2002cx-like SN (SN 2007ie). In
addition, the new compilation includes spectra from 23 confirmed Type II and 8
Type Ib/c SNe.Comment: Accepted for publication in A&
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