296 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
Phenomenology of Neutrino Oscillations
We review the status of several phenomenological topics of current interest
in neutrino oscillations: (i) Solar neutrino oscillations after the first
Sudbury Neutrino Observatory measurements, including both model-independent and
model-dependent results; (ii) Dominant nu_mu-->nu_tau oscillations of
atmospheric and K2K neutrinos, and possible subdominant oscillations induced by
either extra states or extra interactions; and (iii) Four-neutrino scenarios
embedding the controversial LSND evidence for oscillations.Comment: 9 pages, including 12 figures. Presented at TAUP 2001: Topics in
Astroparticle and Underground Physics, Assergi, Italy, 8-12 Sep. 200
Supernova neutrino three-flavor evolution with dominant collective effects
Neutrino and antineutrino fluxes from a core-collapse galactic supernova are
studied, within a representative three-flavor scenario with inverted mass
hierarchy and tiny 1-3 mixing. The initial flavor evolution is dominated by
collective self-interaction effects, which are computed in a full three-family
framework along an averaged radial trajectory. During the whole time span
considered (t=1-20 s), neutrino and antineutrino spectral splits emerge as
dominant features in the energy domain for the final, observable fluxes. Some
minor or unobservable three-family features (e.g., related to the
muonic-tauonic flavor sector) are also discussed for completeness. The main
results can be useful for SN event rate simulations in specific detectors.Comment: 22 pages, including 9 figures (1 section with 3 figures added).
Accepted for publication in JCA
Status of atmospheric neutrino(mu)<-->neutrino(tau) oscillations and decoherence after the first K2K spectral data
We review the status of nu_mu-->nu_tau flavor transitions of atmospheric
neutrinos in the 92 kton-year data sample collected in the first phase of the
Super-Kamiokande (SK) experiment, in combination with the recent spectral data
from the KEK-to-Kamioka (K2K) accelerator experiment (including 29 single-ring
muon events). We consider a theoretical framework which embeds flavor
oscillations plus hypothetical decoherence effects, and where both standard
oscillations and pure decoherence represent limiting cases. It is found that
standard oscillations provide the best description of the SK+K2K data, and that
the associated mass-mixing parameters are determined at 1 sigma (and d.o.f.=1)
as: Delta m^2=(2.6 +- 0.4)x10^{-3} eV^2 and sin^2(2theta)=1.00+0.00-0.05. As
compared with standard oscillations, the case of pure decoherence is
disfavored, although it cannot be ruled out yet. In the general case,
additional decoherence effects in the nu_mu-->nu_tau channel do not improve the
fit to the SK and K2K data, and upper bounds can be placed on the associated
decoherence parameter. Such indications, presently dominated by SK, could be
strengthened by further K2K data, provided that the current spectral features
are confirmed with higher statistics. A detailed description of the statistical
analysis of SK and K2K data is also given, using the so-called ``pull''
approach to systematic uncertainties.Comment: 18 pages (RevTeX) + 12 figures (PostScript
Analysis of oscillations of atmospheric neutrinos
We briefly review the current status of standard oscillations of atmospheric
neutrinos in schemes with two, three, and four flavor mixing. It is shown that,
although the pure \nu_\mu-->\nu_\tau channel provides an excellent 2\nu fit to
the data, one cannot exclude, at present, the occurrence of additional
subleading \nu_\mu-->\nu_e oscillations (3\nu schemes) or of sizable
\nu_\mu-->\nu_s oscillations (4\nu schemes). It is also shown that the wide
dynamical range of energy and pathlength probed by the Super-Kamiokande
experiment puts severe constraints on nonstandard explanations of the
atmospheric neutrino data, with a few notable exceptions.Comment: Talk at the 19th International Conference on Neutrino Physics and
Astrophysics - Neutrino 2000 (Sudbury, Ontario, Canada, 16-21 June 2000
Collective Flavor Oscillations Of Supernova Neutrinos and r-Process Nucleosynthesis
Neutrino-neutrino interactions inside core-collapse supernovae may give rise
to collective flavor oscillations resulting in swap between flavors. These
oscillations depend on the initial energy spectra, and relative fluxes or
relative luminosities of the neutrinos. It has been observed that departure
from energy equipartition among different flavors can give rise to one or more
sharp spectral swap over energy, termed as splits. We study the occurrence of
splits in the neutrino and antineutrino spectra, varying the initial relative
fluxes for different models of initial energy spectrum, in both normal and
inverted hierarchy. These initial relative flux variations give rise to several
possible split patterns whereas variation over different models of energy
spectra give similar results. We explore the effect of these spectral splits on
the electron fraction, , that governs r-process nucleosynthesis inside
supernovae. Since spectral splits modify the electron neutrino and antineutrino
spectra in the region where r-process is postulated to happen, and since the
pattern of spectral splits depends on the initial conditions of the spectra and
the neutrino mass hierarchy, we show that the condition required
for successful r-process nucleosynthesis will lead to constraints on the
initial spectral conditions, for a given neutrino mass hierarchy.Comment: 25 pages, 10 figures, added figure and improved discussion, result
unchanged. Version matches to published version of JCA
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
Evidence for Mikheyev-Smirnov-Wolfenstein effects in solar neutrino flavor transitions
We point out that the recent data from the Sudbury Neutrino Observatory,
together with other relevant measurements from solar and reactor neutrino
experiments, convincingly show that the flavor transitions of solar neutrinos
are affected by Mikheyev-Smirnov-Wolfenstein (MSW) effects. More precisely, one
can safely reject the null hypothesis of no MSW interaction energy in matter,
despite the fact that the interaction amplitude (formally treated as a free
parameter) is still weakly constrained by the current phenomenology. Such a
constraint can be improved, however, by future data from the KamLAND
experiment. In the standard MSW case, we also perform an updated analysis of
two-family active oscillations of solar and reactor neutrinos.Comment: 8 pages + 5 figyre
The solar neutrino problem after three hundred days of data at SuperKamiokande
We present an updated analysis of the solar neutrino problem in terms of both
Mikheyev-Smirnov-Wolfenstein (MSW) and vacuum neutrino oscillations, with the
inclusion of the preliminary data collected by the SuperKamiokande experiment
during 306.3 days of operation. In particular, the observed energy spectrum of
the recoil electrons from 8B neutrino scattering is discussed in detail and is
used to constrain the mass-mixing parameter space. It is shown that: 1) the
small mixing MSW solution is preferred over the large mixing one; 2) the vacuum
oscillation solutions are strongly constrained by the energy spectrum
measurement; and 3) the detection of a possible semiannual modulation of the 8B
\nu flux due to vacuum oscillations should require at least one more year of
operation of SuperKamiokande.Comment: 15 pages (RevTeX) + 8 figures (postscript). Requires epsfig.st
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