1,096 research outputs found
Weak and Electromagnetic Nuclear Decay Signatures for Neutrino Reactions in SuperKamiokande
We suggest the study of events in the SuperKamiokande neutrino data due to
charged- and neutral-current neutrino reactions followed by weak and/or
electromagnetic decays of struck nuclei and fragments thereof. This study could
improve the prospects of obtaining evidence for production from oscillations and could augment the data sample used to disfavor
oscillations.Comment: 7 pages, latex, to appear in Phys. Rev. Let
Solar neutrino measurements in Super-Kamiokande-I
The details of Super--Kamiokande--I's solar neutrino analysis are given.
Solar neutrino measurement in Super--Kamiokande is a high statistics collection
of B solar neutrinos via neutrino-electron scattering. The analysis method
and results of the 1496 day data sample are presented. The final oscillation
results for the data are also presented.Comment: 32pages, 57figures, submitted to Physical Review
The Intrinsic Origin of Spin Echoes in Dipolar Solids Generated by Strong Pi Pulses
In spectroscopy, it is conventional to treat pulses much stronger than the
linewidth as delta-functions. In NMR, this assumption leads to the prediction
that pi pulses do not refocus the dipolar coupling. However, NMR spin echo
measurements in dipolar solids defy these conventional expectations when more
than one pi pulse is used. Observed effects include a long tail in the CPMG
echo train for short delays between pi pulses, an even-odd asymmetry in the
echo amplitudes for long delays, an unusual fingerprint pattern for
intermediate delays, and a strong sensitivity to pi-pulse phase. Experiments
that set limits on possible extrinsic causes for the phenomena are reported. We
find that the action of the system's internal Hamiltonian during any real pulse
is sufficient to cause the effects. Exact numerical calculations, combined with
average Hamiltonian theory, identify novel terms that are sensitive to
parameters such as pulse phase, dipolar coupling, and system size.
Visualization of the entire density matrix shows a unique flow of quantum
coherence from non-observable to observable channels when applying repeated pi
pulses.Comment: 24 pages, 27 figures. Revised from helpful referee comments. Added
new Table IV, new paragraphs on pages 3 and 1
Observation of TeV Gamma Rays from the Crab Nebula with Milagro Using a New Background Rejection Technique
The recent advances in TeV gamma-ray astronomy are largely the result of the
ability to differentiate between extensive air showers generated by gamma rays
and hadronic cosmic rays. Air Cherenkov telescopes have developed and perfected
the "imaging" technique over the past several decades. However until now no
background rejection method has been successfully used in an air shower array
to detect a source of TeV gamma rays. We report on a method to differentiate
hadronic air showers from electromagnetic air showers in the Milagro gamma ray
observatory, based on the ability to detect the energetic particles in an
extensive air shower. The technique is used to detect TeV emission from the
Crab nebula. The flux from the Crab is estimated to be 2.68(+-0.42stat +-
1.4sys) x10^{-7} (E/1TeV)^{-2.59} m^{-2} s^{-1} TeV^{-1}, where the spectral
index is assumed to be as given by the HEGRA collaboration.Comment: 22 pages, 11 figures, submitted to Astrophysical Journa
Solar 8B and hep Neutrino Measurements from 1258 Days of Super-Kamiokande Data
Solar neutrino measurements from 1258 days of data from the Super-Kamiokande
detector are presented. The measurements are based on recoil electrons in the
energy range 5.0-20.0MeV. The measured solar neutrino flux is 2.32 +-
0.03(stat.) +0.08-0.07(sys.)*10^6cm^{-2}s^{-1}, which is
45.1+-0.5(stat.)+1.6-1.4(sys.)% of that predicted by the BP2000 SSM. The day vs
night flux asymmetry is 0.033+-0.022(stat.)+0.013-0.012(sys.). The recoil
electron energy spectrum is consistent with no spectral distortion
(\chi^2/d.o.f. = 19.0/18). The seasonal variation of the flux is consistent
with that expected from the eccentricity of the Earth's orbit (\chi^2/d.o.f. =
3.7/7). For the hep neutrino flux, we set a 90% C.L. upper limit of 40
*10^3cm^{-2}s^{-1}, which is 4.3 times the BP2000 SSM prediction.Comment: 7 pages, 5 figures, submitted to PRL (part of this paper
Milagro Constraints on Very High Energy Emission from Short Duration Gamma-Ray Bursts
Recent rapid localizations of short, hard gamma-ray bursts (GRBs) by the
Swift and HETE satellites have led to the observation of the first afterglows
and the measurement of the first redshifts from this type of burst. Detection
of >100 GeV counterparts would place powerful constraints on GRB mechanisms.
Seventeen short duration (< 5 s) GRBs detected by satellites occurred within
the field of view of the Milagro gamma-ray observatory between 2000 January and
2006 December. We have searched the Milagro data for >100 GeV counterparts to
these GRBs and find no significant emission correlated with these bursts. Due
to the absorption of high-energy gamma rays by the extragalactic background
light (EBL), detections are only expected for redshifts less than ~0.5. While
most long duration GRBs occur at redshifts higher than 0.5, the opposite is
thought to be true of short GRBs. Lack of a detected VHE signal thus allows
setting meaningful fluence limits. One GRB in the sample (050509b) has a likely
association with a galaxy at a redshift of 0.225, while another (051103) has
been tentatively linked to the nearby galaxy M81. Fluence limits are corrected
for EBL absorption, either using the known measured redshift, or computing the
corresponding absorption for a redshift of 0.1 and 0.5, as well as for the case
of z=0.Comment: Accepted for publication in the Astrophysical Journa
Discovery of Localized Regions of Excess 10-TeV Cosmic Rays
An analysis of 7 years of Milagro data performed on a 10-degree angular scale
has found two localized regions of excess of unknown origin with greater than
12 sigma significance. Both regions are inconsistent with gamma-ray emission
with high confidence. One of the regions has a different energy spectrum than
the isotropic cosmic-ray flux at a level of 4.6 sigma, and it is consistent
with hard spectrum protons with an exponential cutoff, with the most
significant excess at ~10 TeV. Potential causes of these excesses are explored,
but no compelling explanations are found.Comment: Submitted to PhysRevLet
A Measurement of the Spatial Distribution of Diffuse TeV Gamma Ray Emission from the Galactic Plane with Milagro
Diffuse -ray emission produced by the interaction of cosmic-ray
particles with matter and radiation in the Galaxy can be used to probe the
distribution of cosmic rays and their sources in different regions of the
Galaxy. With its large field of view and long observation time, the Milagro
Gamma Ray Observatory is an ideal instrument for surveying large regions of the
Northern Hemisphere sky and for detecting diffuse -ray emission at very
high energies. Here, the spatial distribution and the flux of the diffuse
-ray emission in the TeV energy range with a median energy of 15 TeV
for Galactic longitudes between 30 and 110 and between
136 and 216 and for Galactic latitudes between -10 and
10 are determined. The measured fluxes are consistent with predictions
of the GALPROP model everywhere except for the Cygnus region
(). For the Cygnus region, the flux is twice the
predicted value. This excess can be explained by the presence of active cosmic
ray sources accelerating hadrons which interact with the local dense
interstellar medium and produce gamma rays through pion decay.Comment: 15 pages, 3 figures, accepted by Ap
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Time-Integrated Neutrino Source Searches with 10Â Years of IceCube Data.
This Letter presents the results from pointlike neutrino source searches using ten years of IceCube data collected between April 6, 2008 and July 10, 2018. We evaluate the significance of an astrophysical signal from a pointlike source looking for an excess of clustered neutrino events with energies typically above âŒ1ââTeV among the background of atmospheric muons and neutrinos. We perform a full-sky scan, a search within a selected source catalog, a catalog population study, and three stacked Galactic catalog searches. The most significant point in the northern hemisphere from scanning the sky is coincident with the Seyfert II galaxy NGC 1068, which was included in the source catalog search. The excess at the coordinates of NGC 1068 is inconsistent with background expectations at the level of 2.9Ï after accounting for statistical trials from the entire catalog. The combination of this result along with excesses observed at the coordinates of three other sources, including TXS 0506+056, suggests that, collectively, correlations with sources in the northern catalog are inconsistent with background at 3.3Ï significance. The southern catalog is consistent with background. These results, all based on searches for a cumulative neutrino signal integrated over the 10 years of available data, motivate further study of these and similar sources, including time-dependent analyses, multimessenger correlations, and the possibility of stronger evidence with coming upgrades to the detector
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