67 research outputs found
Tests of the Accelerating Universe with Near-Infrared Observations of a High-Redshift Type Ia Supernova
We have measured the rest-frame B,V, and I-band light curves of a
high-redshift type Ia supernova (SN Ia), SN 1999Q (z=0.46), using HST and
ground-based near-infrared detectors.
A goal of this study is the measurement of the color excess, E_{B-I}, which
is a sensitive indicator of interstellar or intergalactic dust which could
affect recent cosmological measurements from high-redshift SNe Ia. Our
observations disfavor a 30% opacity of SN Ia visual light by dust as an
alternative to an accelerating Universe. This statement applies to both
Galactic-type dust
(rejected at the 3.4 sigma confidence level) and greyer dust (grain size >
0.1 microns; rejected at the 2.3 to 2.6 sigma confidence level) as proposed by
Aguirre (1999). The rest-frame -band light cur ve shows the secondary
maximum a month after B maximum typical of nearby SNe Ia of normal luminosi ty,
providing no indication of evolution as a function of redshift out to z~0.5. A
n expanded set of similar observations could improve the constraints on any
contribution of extragalactic dust to the dimming of high-redshift SNe Ia.Comment: Accepted to the Astrophysical Journal, 12 pages, 2 figure
Measurements of the rare decay K_{L} -> e^{+} e^{-} e^{+} e^{-}
We observe 441 K_{L} -> e^{+} e^{-} e^{+} e^{-} candidate events with a
background of 4.2 events and measure B(K_{L} -> e^{+} e^{-} e^{+} e^{-}) =
(3.72 \pm 0.18(stat) \pm 0.23(syst)) \times 10^{-8} in the KTeV/E799II
experiment at Fermilab. Using the distribution of the angle between the planes
of the e^{+} e^{-} pairs, we measure the CP parameters beta_{CP} = -0.23 \pm
0.09(stat) \pm 0.02(syst) and gamma_{CP} = -0.09 \pm 0.09(stat) \pm 0.02(syst).
We also present the first detailed study of the e^{+} e^{-} invariant mass
spectrum in this decay mode.Comment: 14 pages, 4 figure
A Measurement of the Branching Ratio of
We report on a study of the decay carried out as
a part of the KTeV/E799 experiment at Fermilab. The 1997 data yielded a sample
of 1543 events, including an expected background of events. An
effective form factor was determined from the observed distribution of the
invariant mass. Using this form factor in the calculation of the
detector acceptance, the branching ratio was measured to be .Comment: 5 pages, 4 figure
Search for the K(L) --> PI0 PI0 E+ E- Decay in the KTeV Experiment
The recent discovery of a large CP violating asymmetry in K(L) --> PI+ PI- E+
E- mode has prompted us to seach for the associated K(L) --> PI0 PI0 E+ E-
decay mode in the KTeV-E799 experiment at Fermilab. In 2.7E+11 K(L) decays, one
candidate event has been observed with an expected background of 0.3 event,
resulting in an upper limit for the K(L) --> PI0 PI0 E+ E- branching ratio of
6.6E-09 at the 90% confidence level.Comment: To be published in Phys. Rev. Let
A New Measurement of the Radiative Ke3 Branching Ratio and Photon Spectrum
We present a preliminary report on a new measurement of the radiative neutral
Ke3 branching ratio and the first study of the photon spectrum in this decay.
We find BR(Ke3g, E*_g>30 GeV, Th*_eg>20 deg)/BR(Ke3) =
0.911+-0.009(stat)+0.021-0.010(syst)%. Our measurement of the spectrum is
consistent with inner bremsstrahlung only as the source of photons at the 2
sigma level.Comment: 5 pages, 4 figures, proceedings paper from Meson 2000, Cracow,
Poland, May 200
Measurements of Direct CP Violation, CPT Symmetry, and Other Parameters in the Neutral Kaon System
We present a series of measurements based on K -> pi+pi- and K -> pi0pi0
decays collected in 1996-1997 by the KTeV experiment (E832) at Fermilab. We
compare these four K -> pipi decay rates to measure the direct CP violation
parameter Re(e'/e) = (20.7 +- 2.8) x 10^-4. We also test CPT symmetry by
measuring the relative phase between the CP violating and CP conserving decay
amplitudes for K->pi+pi- (phi+-) and for K -> pi0pi0 (phi00). We find the
difference between the relative phases to be Delta-phi = phi00 - phi+- = (+0.39
+- 0.50) degrees and the deviation of phi+- from the superweak phase to be
phi+- - phi_SW =(+0.61 +- 1.19) degrees; both results are consistent with CPT
symmetry. In addition, we present new measurements of the KL-KS mass difference
and KS lifetime: Delta-m = (5261 +- 15) x 10^6 hbar/s and tauS = (89.65 +-
0.07) x 10^-12 s.Comment: Submitted to Phys. Rev. D, August 6, 2002; 37 pages, 32 figure
SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Massive Helium-Shell Detonation in a Star-Forming Galaxy
The detonation of a thin () helium shell
(He-shell) atop a white dwarf (WD) is a promising
mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker
He-shells and less massive WDs may explain some recently observed peculiar SNe
Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the
Zwicky Transient Facility (ZTF). Near maximum light, SN 2020jgb is slightly
subluminous (ZTF -band absolute magnitude between and
mag depending on the amount of host galaxy extinction) and shows an unusually
red color ( between 0.4 and 0.2 mag) due to
strong line-blanketing blueward of 5000 . These properties
resemble those of SN 2018byg, a peculiar SN Ia consistent with a thick He-shell
double detonation (DDet) SN. Using detailed radiative transfer models, we show
that the optical spectroscopic and photometric evolution of SN 2020jgb are
broadly consistent with a (C/O core + He-shell;
up to depending on the total host extinction)
progenitor ignited by a thick () He-shell. We
detect a prominent absorption feature at 1 in the
near-infrared (NIR) spectrum of SN 2020jgb, which could originate from unburnt
helium in the outermost ejecta. While the sample size is limited, similar 1
features have been detected in all the thick He-shell DDet
candidates with NIR spectra obtained to date. SN 2020jgb is also the first
subluminous, thick He-shell DDet SN discovered in a star-forming galaxy,
indisputably showing that He-shell DDet objects occur in both star-forming and
passive galaxies, consistent with the normal SN Ia population.Comment: 23 pages, 10 figures. Updated to accepted version (ApJ
Using equity premium survey data to estimate future wealth
We present the first systematic methods for combining different experts' responses to equity premium surveys. These techniques are based on the observation that the survey data are approximately gamma distributed. This distribution has convenient analytical properties that enable us to address three important problems that investment managers must face. First, we construct probability density functions for the future values of equity index tracker funds. Second, we calculate unbiased and minimum least square error estimators of the future value of these funds. Third, we derive optimal asset allocation weights between equities and the risk-free asset for risk-averse investors. Our analysis allows for both herding and biasedness in expert responses. We show that, unless investors are highly uncertain about expert biases or forecasts are very highly correlated, many investment decisions can be based solely on the mean of the survey data minus any expected bias. We also make recommendations for the design of future equity premium surveys
Machine learning for the Zwicky transient facility
The Zwicky Transient Facility is a large optical survey in multiple filters producing hundreds of thousands of transient alerts per night. We describe here various machine learning (ML) implementations and plans to make the maximal use of the large data set by taking advantage of the temporal nature of the data, and further combining it with other data sets. We start with the initial steps of separating bogus candidates from real ones, separating stars and galaxies, and go on to the classification of real objects into various classes. Besides the usual methods (e.g., based on features extracted from light curves) we also describe early plans for alternate methods including the use of domain adaptation, and deep learning. In a similar fashion we describe efforts to detect fast moving asteroids. We also describe the use of the Zooniverse platform for helping with classifications through the creation of training samples, and active learning. Finally we mention the synergistic aspects of ZTF and LSST from the ML perspective
Branching Ratio Measurement of the decay K_L -> e+ e- mu+ mu-
We have collected a 43 event sample of the decay
with negligible backgrounds and measured its branching ratio to be . We see no evidence for CP violation in this
decay. In addition, we set the 90% confidence upper limit on the combined
branching ratios for the lepton flavor violating decays at , assuming a uniform
phase space distribution
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