32 research outputs found
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
Analytical description of quasivacuum oscillations of solar neutrinos
We propose a simple prescription to calculate the solar neutrino survival
probability P_{ee} in the quasivacuum oscillation (QVO) regime. Such
prescription is obtained by matching perturbative and exact analytical results,
which effectively take into account the density distribution in the Sun as
provided by the standard solar model. The resulting analytical recipe for the
calculation of P_{ee} is shown to reach its highest accuracy |\Delta P_{ee}| <
2.6 x 10^{-2} in the whole QVO range) when the familiar prescription of
choosing the solar density scale parameter r_0 at the
Mikheyev-Smirnov-Wolfenstein (MSW) resonance point is replaced by a new one,
namely, when r_0 is chosen at the point of ``maximal violation of
adiabaticity'' (MVA) along the neutrino trajectory in the Sun. The MVA
prescription admits a smooth transition from the QVO regime to the MSW
transition one. We discuss in detail the phase acquired by neutrinos in the
Sun, and show that it might be of relevance for the studies of relatively short
timescale variations of the fluxes of the solar \nu lines in the future
real-time solar neutrino experiments. Finally, we elucidate the role of matter
effects in the convective zone of the Sun.Comment: 25 pages (RevTeX) + 11 figures (postscript
Three-flavor MSW solutions of the solar neutrino problem
We perform an updated phenomenological analysis of the
Mikheyev-Smirnov-Wolfenstein (MSW) solutions of the solar neutrino problem,
assuming oscillations between two and three neutrino families. The analysis
includes the total rates of the Homestake, SAGE, GALLEX, Kamiokande and
Super-Kamiokande experiments, as well as the day-night asymmetry and the 18-bin
energy spectrum of Super-Kamiokande. Solutions are found at several values of
the theta_{13} mixing angle. Among the most interesting features, we find that
solar neutrino data alone put the constraint theta_{13} < 55--59 deg at 95%
C.L., and that a fraction of the MSW solutions extends at and beyond maximal
(nu_1,nu_2) mixing (theta_{12} > pi/4), especially if the neutrino square mass
splitting is in its lower range (m^2_2-m^2_1 ~ 10^{-7} eV^2) and if theta_{13}
is nonzero. In particular, bimaximal (or nearly bimaximal) mixing is possible
for atmospheric and MSW solar neutrino oscillations within the stringent
reactor bounds on theta_{13}.Comment: 19 pages (RevTeX) + 14 figures (PostScript
Four--Neutrino Oscillation Solutions of the Solar Neutrino Problem
We present an analysis of the neutrino oscillation solutions of the solar
neutrino problem in the framework of four-neutrino mixing where a sterile
neutrino is added to the three standard ones. We perform a fit to the full data
set corresponding to the 825-day Super-Kamiokande data sample as well as to
Chlorine, GALLEX and SAGE and Kamiokande experiments. In our analysis we use
all measured total event rates as well as all Super-Kamiokande data on the
zenith angle dependence and the recoil electron energy spectrum. We consider
both transitions via the Mikheyev-Smirnov-Wolfenstein (MSW) mechanism as well
as oscillations in vacuum (just-so) and find the allowed solutions for
different values of the additional mixing angles. This framework permits
transitions into active or sterile neutrinos controlled by the additional
parameter . We discuss the
maximum allowed values of this additional mixing parameter for the different
solutions.Comment: 28 pages Latex file using RevTeX. 8 postscript figures included
(bitmapped for compression). Detailed explanation of criterion 3 and lower
two graphs of Fig. 8. Misprints corrected in table II.A full version of the
paper can be found at http://ific.uv.es/~penya/papers/four
Neutrino Masses and Mixing: Evidence and Implications
Measurements of various features of the fluxes of atmospheric and solar
neutrinos have provided evidence for neutrino oscillations and therefore for
neutrino masses and mixing. We review the phenomenology of neutrino
oscillations in vacuum and in matter. We present the existing evidence from
solar and atmospheric neutrinos as well as the results from laboratory
searches, including the final status of the LSND experiment. We describe the
theoretical inputs that are used to interpret the experimental results in terms
of neutrino oscillations. We derive the allowed ranges for the mass and mixing
parameters in three frameworks: First, each set of observations is analyzed
separately in a two-neutrino framework; Second, the data from solar and
atmospheric neutrinos are analyzed in a three active neutrino framework; Third,
the LSND results are added, and the status of accommodating all three signals
in the framework of three active and one sterile light neutrinos is presented.
We review the theoretical implications of these results: the existence of new
physics, the estimate of the scale of this new physics and the lessons for
grand unified theories, for supersymmetric models with R-parity violation, for
models of extra dimensions and singlet fermions in the bulk, and for flavor
models.Comment: Added note on the effects of KamLAND results. Two new figure
Testing solar neutrino MSW oscillations at low delta m^2 through time variations of event rates in GNO and BOREXINO
The Mikheyev-Smirnov-Wolfenstein (MSW) explanation of the solar neutrino
problem is currently compatible with three distinct regions of the two-neutrino
oscillation parameter space (delta m^2,sin^2 2theta). We focus on the region
with the lowest value of delta m^2 (~10^{-7} eV^2), which implies significant
Earth regeneration effects for low-energy solar neutrinos. We point out that
such effects are not only observable as day-night variations of neutrino event
rates in the real-time BOREXINO experiment, but also as seasonal variations in
the radiochemical Gallium Neutrino Observatory (GNO) at Gran Sasso. We present
detailed calculations of the difference between winter and summer rates in GNO
(six months averages) in excess of the trivial seasonal variation due to the
Earth orbital eccentricity. We show that, within the low-delta m^2 MSW
solution, the net winter-summer GNO rate difference amounts to 4-6 SNU, with a
dominant contribution from pp neutrinos. We also give analytical expressions
for the winter and summer solar exposure functions at the Gran Sasso site.Comment: 12 pages (RevTeX) + 5 figures (PostScript