A total of 137 upward stopping muons of minimum energy 1.6 GeV are observed by Super-Kamiokande during 516 detector live days. The measured muon flux is
0.39±0.04
(stat.)±0.02
(syst.)×10
−13
cm
−2s
...−1sr
−1
compared to an expected flux of
0.73±0.16
(theo.)×10
−13
cm
−2s
−1sr
−1
. Using our previously-published measurement of the upward through-going muon flux, we calculate the stopping/through-going flux ratio
R
, which has less theoretical uncertainty. The measured value of
R=0.22±0.02
(stat.)±0.01
(syst.)
is significantly smaller than the value 0.37
+0.05
−0.04(theo.) expected using the best theoretical information (the probability that the measured
R
is a statistical fluctuation below the expected value is 0.39%). A simultaneous fitting to zenith angle distributions of upward stopping and through-going muons gives a result which is consistent with the hypothesis of neutrino oscillations with the parameters sin
22
θ>0.7 and 1.5×10
−3<
Δm
2<1.5×10
−2 eV
2 at 90% confidence level, providing a confirmation of the observation of neutrino oscillations by Super-Kamiokande using the contained atmospheric neutrino events.
A new Super-Kamiokande search for supernova relic neutrinos was conducted using 2853 live days of data. Sensitivity is now greatly improved compared to the 2003 Super-Kamiokande result, which placed ...a flux limit near many theoretical predictions. This more detailed analysis includes a variety of improvements such as increased efficiency, a lower energy threshold, and an expanded data set. New combined upper limits on supernova relic neutrino flux are between 2.8 and 3.1nu sub(e) cm super(-2) s super(-1) > 16 MeV total positron energy (17.3 MeV Enu).
The observation of neutrons turning into antineutrons would constitute a discovery of fundamental importance for particle physics and cosmology. Observing the n–n̄ transition would show that baryon ...number (B) is violated by two units and that matter containing neutrons is unstable. It would provide a clue to how the matter in our universe might have evolved from the B=0 early universe. If seen at rates observable in foreseeable next-generation experiments, it might well help us understand the observed baryon asymmetry of the universe. A demonstration of the violation of B–L by 2 units would have a profound impact on our understanding of phenomena beyond the Standard Model of particle physics.
Slow neutrons have kinetic energies of a few meV. By exploiting new slow neutron sources and optics technology developed for materials research, an optimized search for oscillations using free neutrons from a slow neutron moderator could improve existing limits on the free oscillation probability by at least three orders of magnitude. Such an experiment would deliver a slow neutron beam through a magnetically-shielded vacuum chamber to a thin annihilation target surrounded by a low-background antineutron annihilation detector. Antineutron annihilation in a target downstream of a free neutron beam is such a spectacular experimental signature that an essentially background-free search is possible. An authentic positive signal can be extinguished by a very small change in the ambient magnetic field in such an experiment. It is also possible to improve the sensitivity of neutron oscillation searches in nuclei using large underground detectors built mainly to search for proton decay and detect neutrinos.
This paper summarizes the relevant theoretical developments, outlines some ideas to improve experimental searches for free neutron oscillations, and suggests avenues both for theoretical investigation and for future improvement in the experimental sensitivity.
Oscillations in atmospheric neutrinos show no sign of violating a fundamental principle of relativity. A search for neutrino oscillations induced by Lorentz violation has been performed using 4,438 ...live-days of Super-Kamiokande atmospheric neutrino data. The Lorentz violation is included in addition to standard three-flavor oscillations using the nonperturbative standard model extension (SME), allowing the use of the full range of neutrino path lengths, ranging from 15 to 12,800 km, and energies ranging from 100 MeV to more than 100 TeV in the search. No evidence of Lorentz violation was observed, so limits are set on the renormalizable isotropic SME coefficients in the e mu , mu tau, and etau sectors, improving the existing limits by up to 7 orders of magnitude and setting limits for the first time in the neutrino mu tau sector of the SME.
A search for Supernova Relic Neutrinos ν¯e’s is first conducted via inverse-beta-decay by tagging neutron capture on hydrogen at Super-Kamiokande-IV. The neutron tagging efficiency is determined to ...be (17.74±0.04stat.±1.05sys.)%, while the corresponding accidental background probability is (1.06±0.01stat.±0.18sys.)%. Using 960days of data, we obtain 13 inverse-beta-decay candidates in the range of Eν¯e between 13.3MeV and 31.3MeV. All of the observed candidates are attributed to background. Upper limits at 90% C.L. are calculated in the absence of a signal.
We present a real-time supernova neutrino burst monitor at Super-Kamiokande (SK). Detecting supernova explosions by neutrinos in real time is crucial for giving a clear picture of the explosion ...mechanism. Since the neutrinos are expected to come earlier than light, a fast broadcasting of the detection may give astronomers a chance to make electromagnetic radiation observations of the explosions right at the onset. The role of the monitor includes a fast announcement of the neutrino burst detection to the world and a determination of the supernova direction. We present the online neutrino burst detection system and studies of the direction determination accuracy based on simulations at SK.
Purpose: One of available resources for possible improvement of a number of already existing and well developed mammography techniques, without additional dose burden, could be the use of scattering ...radiation. Methods: The authors undertook a preliminary study of the feasibility for applying the forward scattered radiation for determining the percentage of glandular equivalent material or the atomic number (Z) in cases such as Mammography assessment of breast cancer. All measurements made in the study involved a Model 017 mammography phantom. The full spectra of 80 KV x‐ray tube were detected by two solid state CdTe detectors: one in the direction of transmitted beam and the second located at several angles of interest determined by a system of metal collimators. Results: It was determined that the average difference between pure fat equivalent material (0% of glandular equivalent material) and 100% glandular percentage varies by a factor of approximately 8 over the different energy intervals. The intensity of the forward scattered radiation showed a mild decreasing tendency and in certain cases it was independent of the percentage of glandular equivalent material, especially at energies above 40 keV. The calculated ratio of intensities of forward scattered and transmitted radiation is an increasing function of glandular percentage and can be used as an additional index in mammographic diagnosis of breast cancer. Conclusion: The major advantage of the approach described in this study is that the the FS‐T scattering ratio can be applied to selected volumes of interest that are defined by the intersection of the collimated forward scattered and transmitted detectors.
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