18 research outputs found
Indications of Neutrino Oscillation in a 250 km Long-baseline Experiment
The K2K experiment observes indications of neutrino oscillation: a reduction
of flux together with a distortion of the energy spectrum. Fifty-six
beam neutrino events are observed in Super-Kamiokande (SK), 250 km from the
neutrino production point, with an expectation of .
Twenty-nine one ring -like events are used to reconstruct the neutrino
energy spectrum, which is better matched to the expected spectrum with neutrino
oscillation than without. The probability that the observed flux at SK is
explained by statistical fluctuation without neutrino oscillation is less than
1%.Comment: 5 pages, 3 figures embedded, LaTeX with RevTeX style, accepted for
publication in PRL on December 13, 200
Evidence for an oscillatory signature in atmospheric neutrino oscillation
Muon neutrino disappearance probability as a function of neutrino flight
length L over neutrino energy E was studied. A dip in the L/E distribution was
observed in the data, as predicted from the sinusoidal flavor transition
probability of neutrino oscillation. The observed L/E distribution constrained
nu_mu nu_tau neutrino oscillation parameters; 1.9x10^-3 < Delta m^2 <
3.0x10^-3 eV^2 and \sin^2(2theta) > 0.90 at 90% confidence level.Comment: 5 pages, 5 figures, submitted to PR
Search for nucleon decay via modes favored by supersymmetric grand unification models in Super-Kamiokande-I
We report the results for nucleon decay searches via modes favored by
supersymmetric grand unified models in Super-Kamiokande. Using 1489 days of
full Super-Kamiokande-I data, we searched for , , and modes. We found no
evidence for nucleon decay in any of these modes. We set lower limits of
partial nucleon lifetime 2.3, 1.3,
1.3 and 1.0 years at 90% confidence level for , , and modes, respectively. These results give a strong constraint on
supersymmetric grand unification models.Comment: 14 pages, 13 figure
Search for Dark Matter WIMPs using Upward Through-going Muons in Super-Kamiokande
We present the results of indirect searches for Weakly Interacting Massive
Particles (WIMPs) with 1679.6 live days of data from the Super-Kamiokande
detector using neutrino-induced upward through-going muons. The search is
performed by looking for an excess of high energy muon neutrinos from WIMP
annihilations in the Sun, the core of the Earth, and the Galactic Center, as
compared to the number expected from the atmospheric neutrino background. No
statistically significant excess was seen. We calculate flux limits in various
angular cones around each of the above celestial objects. We obtain
conservative model-independent upper limits on WIMP-nucleon cross-section as a
function of WIMP mass and compare these results with the corresponding results
from direct dark matter detection experiments.Comment: 10 pages, 14 figures, Submitted to Phys. Rev.
Search for Supernova Relic Neutrinos at Super-Kamiokande
A search for the relic neutrinos from all past core-collapse supernovae was
conducted using 1496 days of data from the Super-Kamiokande detector. This
analysis looked for electron-type anti-neutrinos that had produced a positron
with an energy greater than 18 MeV. In the absence of a signal, 90% C.L. upper
limits on the total flux were set for several theoretical models; these limits
ranged from 20 to 130 nu_e bar cm^-2 s^-1. Additionally, an upper bound of 1.2
nu_e bar cm^-2 s^-1 was set for the supernova relic neutrino flux in the energy
region E_nu > 19.3 MeV.Comment: 4 pages, 2 figures. Submitted to Physical Review Letters. New version
includes corrections to Figure 1. Also, text has been shortened to conform
with the space limitations of PR
Limit On the Neutrino Magnetic Moment Using 1496 Days of Super-Kamiokande-i Solar Neutrino Data
A search for a non-zero neutrino magnetic moment has been conducted using
1496 live days of solar neutrino data from {\SK}. Specifically, we searched for
distortions to the energy spectrum of recoil electrons arising from magnetic
scattering due to a non-zero neutrino magnetic moment. In the absence of clear
signal, we found at 90% C.L. by
fitting to the Super-Kamiokande day/night spectra. The fitting took into
account the effect of neutrino oscillation on the shapes of energy spectra.
With additional information from other solar neutrino and KamLAND experiments
constraining the oscillation region, a limit of at 90% C.L. was obtained.Comment: 5 pages, 4 figure
A search for periodic modulations of the solar neutrino flux in Super-Kamiokande-I
A search for periodic modulations of the solar neutrino flux was performed
using the Super-Kamiokande-I data taken from May 31st, 1996 to July 15th, 2001.
The detector's capability of measuring the exact time of events, combined with
a relatively high yield of solar neutrino events, allows a search for
short-time variations in the observed flux. We employed the Lomb test to look
for periodic modulations of the observed solar neutrino flux. The obtained
periodogram is consistent with statistical fluctuation and no significant
periodicity was found
Measurement of neutrino oscillation by the K2K experiment
We present measurements of nu(mu) disappearance in K2K, the KEK to Kamioka long-baseline neutrino oscillation experiment. One-hundred and twelve beam-originated neutrino events are observed in the fiducial volume of Super-Kamiokande with an expectation of 158.1(-8.6)(+9.2) events without oscillation. A distortion of the energy spectrum is also seen in 58 single-ring muonlike events with reconstructed energies. The probability that the observations are explained by the expectation for no neutrino oscillation is 0.0015% (4.3 sigma). In a two-flavor oscillation scenario, the allowed Delta m(2) region at sin(2)2 theta=1 is between 1.9 and 3.5x10(-3) eV(2) at the 90% C.L. with a best-fit value of 2.8x10(-3) eV(2)
Detailing the optimality of photosynthesis in cyanobacteria through systems biology analysis
Photosynthesis has recently gained considerable attention for its potential role in the development of renewable energy sources. Optimizing photosynthetic organisms for biomass or biofuel production will therefore require a systems understanding of photosynthetic processes. We reconstructed a high-quality genome-scale metabolic network for Synechocystis sp. PCC6803 that describes key photosynthetic processes in mechanistic detail. We performed an exhaustive in silico analysis of the reconstructed photosynthetic process under different light and inorganic carbon (Ci) conditions as well as under genetic perturbations. Our key results include the following. (i) We identified two main states of the photosynthetic apparatus: a Ci-limited state and a light-limited state. (ii) We discovered nine alternative electron flow pathways that assist the photosynthetic linear electron flow in optimizing the photosynthesis performance. (iii) A high degree of cooperativity between alternative pathways was found to be critical for optimal autotrophic metabolism. Although pathways with high photosynthetic yield exist for optimizing growth under suboptimal light conditions, pathways with low photosynthetic yield guarantee optimal growth under excessive light or Ci limitation. (iv) Photorespiration was found to be essential for the optimal photosynthetic process, clarifying its role in high-light acclimation. Finally, (v) an extremely high photosynthetic robustness drives the optimal autotrophic metabolism at the expense of metabolic versatility and robustness. The results and modeling approach presented here may promote a better understanding of the photosynthetic process. They can also guide bioengineering projects toward optimal biofuel production in photosynthetic organisms