37 research outputs found
How two neutrino superbeam experiments do better than one
We examine the use of two superbeam neutrino oscillation experiments with
baselines \lsim 1000 km to resolve parameter degeneracies inherent in the
three-neutrino analysis of such experiments. We find that with appropriate
choices of neutrino energies and baselines two experiments with different
baselines can provide a much better determination of the neutrino mass ordering
than a single experiment alone. Two baselines are especially beneficial when
the mass scale for solar neutrino oscillations is \gsim
5\times10^{-5} eV. We also examine CP violation sensitivity and the
resolution of other parameter degeneracies. We find that the combined data of
superbeam experiments with baselines of 295 and 900 km can provide sensitivity
to both the neutrino mass ordering and CP violation for
down to 0.03 for eV. It
would be highly advantageous to have a 10% determination of before the beam energies and baselines are finalized, although if
is not that well known, the neutrino energies and
baselines can be chosen to give fairly good sensitivity for a range of .Comment: 18 pages, 6 PS figures, added references and revised discussio
Piecing the Solar Neutrino Puzzle Together at SNO
We perform an oscillation parameter-independent analysis of solar neutrino
flux measurements from which we predict the charged-current rate at SNO
relative to Standard Solar Model to be for oscillations to active (sterile) neutrinos. By
alternately considering the B flux normalization fixed and free, we find
that the flux measured by Super-Kamiokande (SK) not being a result of
oscillations is strongly disfavored for oscillations to active neutrinos. SNO
will determine the best-fit value of the B flux normalization
(equal to the neutral-current rate), without recourse to neutral-current
measurements, from the derived relation . Using a simple parameterization of the fraction of high,
intermediate, and low energy solar neutrinos starting above resonance, we
reproduce the results of global analyses to good accuracy; we find that the LMA
solution with a normal mass hierarchy is clearly favored. With free,
our analysis for oscillations to active neutrinos gives
, which corresponds to .Comment: Version to appear in PL
Unknowns after the SNO Charged-Current Measurement
We perform a model-independent analysis of solar neutrino flux rates
including the recent charged-current measurement at the Sudbury Neutrino
Observatory (SNO). We derive a universal sum rule involving SNO and
SuperKamiokande rates, and show that the SNO neutral-current measurement can
not fix the fraction of solar oscillating to sterile neutrinos. The
large uncertainty in the SSM B flux impedes a determination of the sterile
neutrino fraction.Comment: Version to appear in PRL; includes analysis with anticipated SNO NC
measuremen
Confronting mass-varying neutrinos with MiniBooNE
We study the proposal that mass-varying neutrinos could provide an
explanation for the LSND signal for \bar\nu_mu to \bar\nu_e oscillations. We
first point out that all positive oscillation signals occur in matter and that
three active mass-varying neutrinos are insufficient to describe all existing
neutrino data including LSND. We then examine the possibility that a model with
four mass-varying neutrinos (three active and one sterile) can explain the LSND
effect and remain consistent with all other neutrino data. We find that such
models with a 3+1 mass structure in the neutrino sector may explain the LSND
data and a null MiniBooNE result for 0.10 < \sin^2 2\theta_x < 0.30.
Predictions of the model include a null result at Double-CHOOZ, but positive
signals for underground reactor experiments and for \nu_\mu to \nu_e
oscillations in long-baseline experiments.Comment: 22 pages, 3 figures, 1 table. Comment added about recent MINOS dat
Breaking Eight-fold Degeneracies in Neutrino CP Violation, Mixing, and Mass Hierarchy
We identify three independent two-fold parameter degeneracies (\delta,
\theta_{13}), sgn(\delta m^2_{31}) and (\theta_{23}, \pi/2-\theta_{23})
inherent in the usual three-neutrino analysis of long-baseline neutrino
experiments, which can lead to as much as an eight-fold degeneracy in the
determination of the oscillation parameters. We discuss the implications these
degeneracies have for detecting CP violation and present criteria for breaking
them. A superbeam facility with a baseline at least as long as the distance
between Fermilab and Homestake (1290 km) and a narrow band beam with energy
tuned so that the measurements are performed at the first oscillation peak can
resolve all the ambiguities other than the (\theta_{23}, \pi/2-\theta_{23})
ambiguity (which can be resolved at a neutrino factory) and a residual (\delta,
\pi-\delta) ambiguity. However, whether or not CP violation occurs in the
neutrino sector can be ascertained independently of the latter two ambiguities.
The (\delta,\pi-\delta) ambiguity can be eliminated by performing a second
measurement to which only the \cos\delta terms contribute. The hierarchy of
mass eigenstates can be determined at other oscillation peaks only in the most
optimistic conditions, making it necessary to use the first oscillation
maximum. We show that the degeneracies may severely compromise the ability of
the proposed SuperJHF-HyperKamiokande experiment to establish CP violation. In
our calculations we use approximate analytic expressions for oscillation
probabilitites that agree with numerical solutions with a realistic Earth
density profile.Comment: Revtex (singlespaced), 35 pages, 15 postscript figures, uses
psfig.st
Imprint of SNO neutral current data on the solar neutrino problem
We perform a global analysis in the framework of two active neutrino
oscillations of all solar neutrino data, including the recent SNO day and night
spectra (comprised of the charged current (CC), elastic scattering (ES) and
neutral current (NC) events), the Super-Kamiokande (SK) day and night spectra
(from 1496 days) and the updated SAGE results. We find that the Large Mixing
Angle (LMA) solution is selected at the 99% C.L.; the best-fit parameters are
\Delta m^2=5.6 \times 10^{-5} eV^2 and \theta=32^{\circ}. No solutions with
\theta\geq \pi/4 are allowed at the 5\sigma C.L. Oscillations to a pure sterile
state are excluded at 5.3\sigma, but a sizeable sterile neutrino component
could still be present in the solar flux.Comment: Version to appear in PL