104 research outputs found
Three-flavor solar neutrino oscillations with terrestrial neutrino constraints
We present an updated analysis of the current solar neutrino data in terms of
three-flavor oscillations, including the additional constraints coming from
terrestrial neutrino oscillation searches at the CHOOZ (reactor),
Super-Kamiokande (atmospheric), and KEK-to-Kamioka (accelerator) experiments.
The best fit is reached for the subcase of two-family mixing, and the
additional admixture with the third neutrino is severely limited. We discuss
the relevant features of the globally allowed regions in the oscillation
parameter space, as well as their impact on the amplitude of possible
CP-violation effects at future accelerator experiments and on the
reconstruction accuracy of the mass-mixing oscillation parameters at the
KamLAND reactor experiment.Comment: 10 pages + 8 figure
Quasi-energy-independent solar neutrino transitions
Current solar, atmospheric, and reactor neutrino data still allow oscillation
scenarios where the squared mass differences are all close to 10^-3 eV^2,
rather than being hierarchically separated. For solar neutrinos, this situation
(realized in the upper part of the so-called large-mixing angle solution)
implies adiabatic transitions which depend weakly on the neutrino energy and on
the matter density, as well as on the ``atmospheric'' squared mass difference.
In such a regime of ``quasi-energy-independent'' (QEI) transitions,
intermediate between the more familiar ``Mikheyev-Smirnov-Wolfenstein'' (MSW)
and energy-independent (EI) regimes, we first perform analytical calculations
of the solar nu_e survival probability at first order in the matter density,
beyond the usual hierarchical approximations. We then provide accurate,
generalized expressions for the solar neutrino mixing angles in matter, which
reduce to those valid in the MSW, QEI and EI regimes in appropriate limits.
Finally, a representative QEI scenario is discussed in some detail.Comment: Title changed; text and acronyms revised; results unchanged. To
appear in PR
On the Size of the Dark Side of the Solar Neutrino Parameter Space
We present an analysis of the MSW neutrino oscillation solutions of the solar
neutrino problem in the framework of two-neutrino mixing in the enlarged
parameter space with . Recently, it was pointed out that the allowed region of
parameters from a fit to the measured total rates can extend to values (the so called ``dark side'') when higher confidence levels
are allowed. The purpose of this letter is to reanalize the problem including
all the solar neutrino data available, to discuss the dependence on the
statistical criteria in the determination of the CL of the ``dark side'' and to
extract the corresponding limits on the largest mixing allowed by the data. Our
results show that when the Super-Kamiokande data on the zenith angle
distribution of events and the spectrum information is included, the regions
extend more into the dark side.Comment: 5 pages,latex file using RevTex. Two-layer aproximation for the Earth
density replaced by numerical integration with PREM. Latest parametrization
of the sun matter density (BP2000) is included. Misprints corrected.
Conclusions unchanged. 5 postscript figures (bitmapped for compression). A
full version of the paper can be found at http://ific.uv.es/~penya/papers/ To
appear in Phys. Rev.
Solar neutrino oscillations and indications of matter effects in the Sun
Assuming the current best-fit solutions to the solar neutrino problem at
large mixing angle, we briefly illustrate how prospective data from the Sudbury
Neutrino Observatory (SNO) and from the Kamioka Liquid scintillator
Anti-Neutrino Detector (KamLAND) can increase our confidence in the occurrence
of standard matter effects on active neutrino flavor oscillations in the Sun,
which are starting to emerge from current data.Comment: Updated to include the first KamLAND data. One figure adde
Solar neutrino event spectra: Tuning SNO to equalize Super-Kamiokande
The Super-Kamiokande (SK) and the Sudbury Neutrino Observatory (SNO)
experiments are monitoring the flux of B solar neutrinos through the electron
energy spectrum from the reactions nu_{e,mu,tau} + e --> nu_{e,mu,tau} + e and
nu_e + d --> p + p + e, respectively. We show that the SK detector response to
B neutrinos in each bin of the electron energy spectrum (above 8 MeV) can be
approximated, with good accuracy, by the SNO detector response in an
appropriate electron energy range (above 5.1 MeV). For instance, the SK
response in the bin [10,10.5] MeV is reproduced (``equalized'') within 2
percent by the SNO response in the range [7.1,11.75] MeV. As a consequence, in
the presence of active neutrino oscillations, the SK and SNO event rates in the
corresponding energy ranges turn out to be linearly related, for any functional
form of the oscillation probability. Such equalization is not spoiled by the
possible contribution of hep neutrinos (within current phenomenological
limits). In perspective, when the SK and the SNO spectra will both be measured
with high accuracy, the SK-SNO equalization can be used to determine the
absolute B neutrino flux, and to cross-check the (non)observation of spectral
deviations in SK and SNO. At present, as an exercise, we use the equalization
to ``predict'' the SNO energy spectrum, on the basis of the current SK data.
Finally, we briefly discuss some modifications or limitations of our results in
the case of sterile neutrino oscillations and of relatively large Earth matter
effects.Comment: 18 pages + 6 figure
Implications of recent solar neutrino observations: an analysis of charged current data
We have analysed the recent results from the observation of charged current
\nu_e d \to e^- p p events from solar neutrinos by the Sudbury Neutrino
Observatory SNO assuming neutrino oscillations with three active flavours. The
data seem to prefer a low mass-squared difference and large mixing angle
solution (the so-called LOW solution) in (12) parameter space. However, when
combined with the Gallium charged current interaction data from Gallex and GNO,
distinct (1\sigma) allowed regions corresponding to the large mixing angle
(LMA) and small mixing angle (SMA) appear while the LOW solution is disfavoured
upto 3\sigma standard deviation. The physical electron neutrino survival
probability corresponding to these best fit solutions are then determined and
analysed for their energy dependence.Comment: 16 pages Latex file, with 5 epsf figures; one reference adde
Constraints on Neutrino Parameters from Neutral-Current Solar Neutrino Measurements
We generalize the pull approach to define the function to the
analysis of the data with correlated statistical errors. We apply this method
to the analysis of the Sudbury Neutrino Collaboration data obtained in the
salt-phase. In the global analysis of all the solar neutrino and KamLAND data
we find the best fit (minimum ) values of neutrino parameters to be
and
eV. We confirm that the maximal mixing is strongly disfavored while the
bounds on are significantly strengthened.Comment: 6 figures. Some typos are corrected, figures are visually improve
Energy Independent Solution to the Solar Neutrino Anomaly including the SNO data
The global data on solar neutrino rates and spectrum, including the SNO
charged current rate, can be explained by LMA, LOW or the energy independent
solution -- corresponding to near-maximal mixing. All the three favour a mild
upward renormalisation of the Cl rate. A mild downward shift of the
neutrino flux is favoured by the energy independent and to a lesser extent the
LOW solution, but not by LMA. Comparison with the ratio of SK elastic and SNO
charged current scattering rates favours the LMA over the other two solutions,
but by no more than .Comment: 18 pages, latex, 3 figure
Violation of the Equivalence Principle in the light of the SNO and SK solar neutrino results
The SNO result on charged current deuteron disintegration, the
SuperKamiokande 1258-day data on electron scattering, and other solar neutrino
results are used to revisit the model of neutrino oscillations driven by a
violation of the equivalence principle. We use a chisq minimization technique
to examine oscillation between the nu(e) and another active neutrino, both
massless, and find that within the Standard Solar Model the fit to the SNO and
SuperKamiokande spectra are moderately good while a very good fit is obtained
when the absolute normalizations of the 8B and hep neutrino fluxes are allowed
to vary. The best fit prefers large, but not maximal, mixing, essentially no
hep neutrinos, and a 40% reduction in the 8B neutrino flux. The fit to the
total rates from the different experiments is not encouraging but when the
rates and spectra are considerd together the situation is much improved. We
remark on the expectations of the VEP model for the neutral current
measurements at SNO.Comment: Latex, 11 pages (incl. 1 postscript figure
Solar Neutrino Rates, Spectrum, and its Moments : an MSW Analysis in the Light of Super-Kamiokande Results
We re-examine MSW solutions of the solar neutrino problem in a two flavor
scenario taking (a) the results on total rates and the electron energy spectrum
from the 1117-day SuperKamiokande (SK) data and (b) those on total rates from
the Chlorine and Gallium experiments. We find that the SMA solution gives the
best fit to the total rates data from the different experiments. One new
feature of our analysis is the use of the moments of the SK electron spectrum
in a analysis. The best-fit to the moments is broadly in agreement
with that obtained from a direct fit to the spectrum data and prefers a comparable to the SMA fit to the rates but the required mixing angle is
larger. In the combined rate and spectrum analysis, apart from varying the
normalization of the B flux as a free parameter and determining its
best-fit value we also obtain the best-fit parameters when correlations between
the rates and the spectrum data are included and the normalization of the B
flux held fixed at its SSM value. We observe that the correlations between the
rates and spectrum data are important and the goodness of fit worsens when
these are included. In either case, the best-fit lies in the LMA region.Comment: 17 pages, 4 figure
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