9 research outputs found
Constraining the absolute neutrino mass scale and Majorana CP violating phases by future neutrinoless double beta decay experiments
Assuming that neutrinos are Majorana particles, in a three generation
framework, current and future neutrino oscillation experiments can determine
six out of the nine parameters which fully describe the structure of the
neutrino mass matrix. We try to clarify the interplay among the remaining
parameters, the absolute neutrino mass scale and two CP violating Majorana
phases, and how they can be accessed by future neutrinoless double beta
() decay experiments, for the normal as well as for the
inverted order of the neutrino mass spectrum. Assuming the oscillation
parameters to be in the range presently allowed by atmospheric, solar, reactor
and accelerator neutrino experiments, we quantitatively estimate the bounds on
, the lightest neutrino mass, that can be infered if the next generation
decay experiments can probe the effective Majorana mass
() down to
1 meV. In this context we conclude that in the case neutrinos are
Majorana particles: (a) if m_0 \gsim 300 meV, {\em i.e.}, within the range
directly attainable by future laboratory experiments as well as astrophysical
observations, then m_{ee} \gsim 30 meV must be observed;
(b) if meV, results from future decay
experiments combined with stringent bounds on the neutrino oscillation
parameters, specially the solar ones, will place much stronger limits on the
allowed values of than these direct experiments.Comment: 26 pages, 11 encapsulated postscript figures. A new figure and minor
changes are included. To be published in Phys. Rev.
Resolving theta_{23} Degeneracy by Accelerator and Reactor Neutrino Oscillation Experiments
If the lepton mixing angle theta_{23} is not maximal, there arises a problem
of ambiguity in determining theta_{23} due to the existence of two degenerate
solutions, one in the first and the other in the second octant. We discuss an
experimental strategy for resolving the theta_{23} octant degeneracy by
combining reactor measurement of theta_{13} with accelerator nu_{mu}
disappearance and nu_{e} appearance experiments. The robustness of the
theta_{23} degeneracy and the difficulty in lifting it only by accelerator
experiments with conventional nu_{mu} (and nu_{mu}-bar) beam are demonstrated
by analytical and numerical treatments. Our method offers a way to overcome the
difficulty and can resolve the degeneracy between solutions sin^2 theta_{23} =
0.4 and sin^2 theta_{23} = 0.6 if sin^2 (2 theta_{13}) \gsim 0.05 at 95% CL by
assuming the T2K phase II experiment and a reactor measurement with an exposure
of 10 GW.kt.yr. The dependence of the resolving power of the octant degeneracy
on the systematic errors of reactor experiments is also examined.Comment: 23 pages, 9 figures, version to appear in PR
Reactor Measurement of theta_12; Principles, Accuracies and Physics Potentials
We discuss reactor measurement of \theta_{12} which has a potential of
reaching the ultimate sensitivity which surpasses all the methods so far
proposed. The key is to place a detector at an appropriate baseline distance
from the reactor neutrino source to have an oscillation maximum at around a
peak energy of the event spectrum in the absence of oscillation. By a detailed
statistical analysis the optimal distance is estimated to be \simeq (50-70) km
x [8 x 10^{-5} eV^2/\Delta m^2_{21}], which is determined by maximizing the
oscillation effect in the event number distribution and minimizing geo-neutrino
background contamination. To estimate possible uncertainty caused by
surrounding nuclear reactors in distance of \sim 100 km, we examine a concrete
example of a detector located at Mt. Komagatake, 54 km away from the
Kashiwazaki-Kariwa nuclear power plant in Japan, the most powerful reactor
complex in the world. The effect turns out to be small. Under a reasonable
assumption of systematic error of 4% in the experiment, we find that
sin^2{\theta_{12}} can be determined to the accuracy of \simeq 2% (\simeq 3%),
at 68.27% CL for 1 degree of freedom, for 60 GW_th kton yr (20 GW_th kton yr)
operation. We also discuss implications of such an accurate measurement of
\theta_{12}.Comment: 31 pages, 8 figures. version to appear in PR
Supernova Neutrino-Nucleus Astrophysics
In this brief review we explore the role of neutrino-nucleus interactions in
core-collapse supernovae and discuss open questions. In addition implications
of neutrino mass and mixings in such environments are summarized.Comment: Revtex 4 figure