25 research outputs found
Constraints on Nucleon Decay via "Invisible" Modes from the Sudbury Neutrino Observatory
Data from the Sudbury Neutrino Observatory have been used to constrain the
lifetime for nucleon decay to ``invisible'' modes, such as n -> 3 nu. The
analysis was based on a search for gamma-rays from the de-excitation of the
residual nucleus that would result from the disappearance of either a proton or
neutron from O16. A limit of tau_inv > 2 x 10^{29} years is obtained at 90%
confidence for either neutron or proton decay modes. This is about an order of
magnitude more stringent than previous constraints on invisible proton decay
modes and 400 times more stringent than similar neutron modes.Comment: Update includes missing efficiency factor (limits change by factor of
2) Submitted to Physical Review Letter
Measurement of the Total Active 8B Solar Neutrino Flux at the Sudbury Neutrino Observatory with Enhanced Neutral Current Sensitivity
The Sudbury Neutrino Observatory (SNO) has precisely determined the total
active (nu_x) 8B solar neutrino flux without assumptions about the energy
dependence of the nu_e survival probability. The measurements were made with
dissolved NaCl in the heavy water to enhance the sensitivity and signature for
neutral-current interactions. The flux is found to be 5.21 +/- 0.27 (stat) +/-
0.38 (syst) x10^6 cm^{-2}s^{-1}, in agreement with previous measurements and
standard solar models. A global analysis of these and other solar and reactor
neutrino results yields Delta m^{2} = 7.1^{+1.2}_{-0.6}x10^{-5} ev^2 and theta
= 32.5^{+2.4}_{-2.3} degrees. Maximal mixing is rejected at the equivalent of
5.4 standard deviations.Comment: Submitted to Phys. Rev. Let
Electron Antineutrino Search at the Sudbury Neutrino Observatory
Upper limits on the \nuebar flux at the Sudbury Neutrino Observatory have
been set based on the \nuebar charged-current reaction on deuterium. The
reaction produces a positron and two neutrons in coincidence. This distinctive
signature allows a search with very low background for \nuebar's from the Sun
and other potential sources. Both differential and integral limits on the
\nuebar flux have been placed in the energy range from 4 -- 14.8 MeV. For an
energy-independent \nu_e --> \nuebar conversion mechanism, the integral limit
on the flux of solar \nuebar's in the energy range from 4 -- 14.8 MeV is found
to be \Phi_\nuebar <= 3.4 x 10^4 cm^{-2} s^{-1} (90% C.L.), which corresponds
to 0.81% of the standard solar model 8B \nu_e flux of 5.05 x 10^6 cm^{-2}
s^{-1}, and is consistent with the more sensitive limit from KamLAND in the 8.3
-- 14.8 MeV range of 3.7 x 10^2 cm^{-2} s^{-1} (90% C.L.). In the energy range
from 4 -- 8 MeV, a search for \nuebar's is conducted using coincidences in
which only the two neutrons are detected. Assuming a \nuebar spectrum for the
neutron induced fission of naturally occurring elements, a flux limit of
Phi_\nuebar <= 2.0 x 10^6 cm^{-2} s^{-1}(90% C.L.) is obtained.Comment: submitted to Phys. Rev.
Measurement of the and Total B Solar Neutrino Fluxes with the Sudbury Neutrino Observatory Phase I Data Set
This article provides the complete description of results from the Phase I
data set of the Sudbury Neutrino Observatory (SNO). The Phase I data set is
based on a 0.65 kt-year exposure of heavy water to the solar B neutrino
flux. Included here are details of the SNO physics and detector model,
evaluations of systematic uncertainties, and estimates of backgrounds. Also
discussed are SNO's approach to statistical extraction of the signals from the
three neutrino reactions (charged current, neutral current, and elastic
scattering) and the results of a search for a day-night asymmetry in the
flux. Under the assumption that the B spectrum is undistorted, the
measurements from this phase yield a solar flux of cm s, and a non- component
cm s. The sum of these components provides a
total flux in excellent agreement with the predictions of Standard Solar
Models. The day-night asymmetry in the flux is found to be , when the asymmetry in
the total flux is constrained to be zero.Comment: Complete (archival) version of SNO Phase I results. 78 pages, 46
figures, 34 table
Constraints on Nucleon Decay via “Invisible” Modes from the Sudbury Neutrino Observatory
Data from the Sudbury Neutrino Observatory have been used to constrain the lifetime for nucleon decay to “invisible” modes, such as n -> 3v. The analysis was based on a search for y-rays from the de-excitation of the residual nucleus that would result from the disappearance of either a proton or neutron from ^16O. A limit of t inv > 2×1029 years is obtained at 90% confidence for either neutron or proton decay modes. This is about an order of magnitude more stringent than previous constraints on invisible proton decay modes and 400 times more stringent than similar neutron modes
Mapping Temperate Vegetation Climate Adaptation Variability Using Normalized Land Surface Phenology
Climate influences geographic differences of vegetation phenology through both contemporary and historical variability. The latter effect is embodied in vegetation heterogeneity underlain by spatially varied genotype and species compositions tied to climatic adaptation. Such long-term climatic effects are difficult to map and therefore often neglected in evaluating spatially explicit phenological responses to climate change. In this study we demonstrate a way to indirectly infer the portion of land surface phenology variation that is potentially contributed by underlying genotypic differences across space. The method undertaken normalized remotely sensed vegetation start-of-season (or greenup onset) with a cloned plants-based phenological model. As the geography of phenological model prediction (first leaf) represents the instantaneous effect of contemporary climate, the normalized land surface phenology potentially reveals vegetation heterogeneity that is related to climatic adaptation. The study was done at the continental scale for the conterminous U.S., with a focus on the eastern humid temperate domain. Our findings suggest that, in an analogous scenario, if a uniform contemporary climate existed everywhere, spring vegetation greenup would occur earlier in the north than in the south. This is in accordance with known species-level clinal variations—for many temperate plant species, populations adapted to colder climates require less thermal forcing to initiate growth than those in warmer climates. This study, for the first time, shows that such geographic adaption relationships are supported at the ecosystem level. Mapping large-scale vegetation climate adaptation patterns contributes to our ability to better track geographically varied phenological responses to climate change
Effects of Simulated Smog Atmospheres in Rodent Models of Metabolic and Immunologic Dysfunction
Air
pollution is a diverse and dynamic mixture of gaseous and particulate
matter, limiting our understanding of associated adverse health outcomes.
The biological effects of two simulated smog atmospheres (SA) with
different compositions but similar air quality health indexes were
compared in a nonobese diabetic rat model (Goto-Kakizaki, GK) and
three mouse immune models (house dust mite (HDM) allergy, antibody
response to heat-killed pneumococcus, and resistance to influenza
A infection). In GK rats, both SA-PM (high particulate matter) and
SA-O<sub>3</sub> (high ozone) decreased cholesterol levels immediately
after a 4-h exposure, whereas only SA-O<sub>3</sub> increased airflow
limitation. Airway responsiveness to methacholine was increased in
HDM-allergic mice compared with nonallergic mice, but exposure to
SA-PM or SA-O<sub>3</sub> did not significantly alter responsiveness.
Exposure to SA-PM did not affect the IgM response to pneumococcus,
and SA-O<sub>3</sub> did not affect virus titers, although inflammatory
cytokine levels were decreased in mice infected at the end of a 7-day
exposure. Collectively, acute SA exposures produced limited health
effects in animal models of metabolic and immune diseases. Effects
of SA-O<sub>3</sub> tended to be greater than those of SA-PM, suggesting
that gas-phase components in photochemically derived multipollutant
mixtures may be of greater concern than secondary organic aerosol
PM