564 research outputs found
Probing supernova physics with neutrino oscillations
We point out that solar neutrino oscillations with large mixing angle as
evidenced in current solar neutrino data have a strong impact on strategies for
diagnosing collapse-driven supernova (SN) through neutrino observations. Such
oscillations induce a significant deformation of the energy spectra of
neutrinos, thereby allowing us to obtain otherwise inaccessible features of SN
neutrino spectra. We demonstrate that one can determine temperatures and
luminosities of non-electron flavor neutrinos by observing bar{nu}_{e} from
galactic SN in massive water Cherenkov detectors by the charged current
reactions on protons.Comment: 6 pages. Typos corrected and references added. Version to be
published in Physics Letters
What can we learn about the lepton CP phase in the next 10 years?
We discuss how the lepton CP phase can be constrained by accelerator and
reactor measurements in an era without dedicated experiments for CP violation
search. To characterize globally the sensitivity to the CP phase \delta_{CP},
we introduce a new measure, the CP exclusion fraction, which quantifies what
fraction of the \delta_{CP} space can be excluded at a given input values of
\theta_{23} and \delta_{CP}. Using the measure we study the CP sensitivity
which may be possessed by the accelerator experiments T2K and NOvA. We show
that, if the mass hierarchy is known, T2K and NOvA alone may exclude,
respectively, about 50%-60% and 40%-50% of the \delta_{CP} space at 90% CL by
10 years running, provided that a considerable fraction of beam time is devoted
to the antineutrino run. The synergy between T2K and NOvA is remarkable,
leading to the determination of the mass hierarchy through CP sensitivity at
the same CL.Comment: Analyses and plots improved, conclusions unchanged, 23 pages, 8
figures, 1 tabl
Parameter Degeneracies in Neutrino Oscillation Measurement of Leptonic CP and T Violation
The measurement of the mixing angle \theta_{13}, sign of \Delta m^2_{13} and
the CP or T violating phase \delta is fraught with ambiguities in neutrino
oscillation. In this paper we give an analytic treatment of the paramater
degeneracies associated with measuring the \nu_\mu -> \nu_e probability and its
CP and/or T conjugates. For CP violation, we give explicit solutions to allow
us to obtain the regions where there exist two-fold and four-fold degeneracies.
We calculate the fractional differences, \Delta \theta / \bar{\theta}, between
the allowed solutions which may be used to compare with the expected
sensitivities of the experiments. For T violation we show that there is always
a complete degeneracy between solutions with positive and negative \Delta
m^2_{13} which arises due to a symmetry and cannot be removed by observing one
neutrino oscillation probability and its T conjugate. Thus, there is always a
four fold parameter degeneracy apart from exceptional points. Explicit
solutions are also given and the fractional differences are computed. The
bi-probability CP/T trajectory diagrams are extensively used to illuminate the
nature of the degeneracies.Comment: 35 pages, Latex, 11 postscript figures, minor correction
Large-Theta(13) Perturbation Theory of Neutrino Oscillation for Long-Baseline Experiments
The Cervera et al. formula, the best known approximate formula of neutrino
oscillation probability for long-baseline experiments, can be regarded as a
second-order perturbative formula with small expansion parameter epsilon \equiv
Delta m^2_{21} / Delta m^2_{31} \simeq 0.03 under the assumption s_{13} \simeq
epsilon. If theta_{13} is large, as suggested by a candidate nu_{e} event at
T2K as well as the recent global analyses, higher order corrections of s_{13}
to the formula would be needed for better accuracy. We compute the corrections
systematically by formulating a perturbative framework by taking theta_{13} as
s_{13} \sim \sqrt{epsilon} \simeq 0.18, which guarantees its validity in a wide
range of theta_{13} below the Chooz limit. We show on general ground that the
correction terms must be of order epsilon^2. Yet, they nicely fill the mismatch
between the approximate and the exact formulas at low energies and relatively
long baselines. General theorems are derived which serve for better
understanding of delta-dependence of the oscillation probability. Some
interesting implications of the large theta_{13} hypothesis are discussed.Comment: Fig.2 added, 23 pages. Matches to the published versio
Determining Neutrino Mass Hierarchy by Precision Measurements in Electron and Muon Neutrino Disappearance Experiments
Recently a new method for determining the neutrino mass hierarchy by
comparing the effective values of the atmospheric \Delta m^2 measured in the
electron neutrino disappearance channel, \Delta m^2(ee), with the one measured
in the muon neutrino disappearance channel, \Delta m^2(\mu \mu), was proposed.
If \Delta m^2(ee) is larger (smaller) than \Delta m^2(\mu \mu) the hierarchy is
of the normal (inverted) type. We re-examine this proposition in the light of
two very high precision measurements: \Delta m^2(\mu \mu) that may be
accomplished by the phase II of the Tokai-to-Kamioka (T2K) experiment, for
example, and \Delta m^2(ee) that can be envisaged using the novel Mossbauer
enhanced resonant \bar\nu_e absorption technique. Under optimistic assumptions
for the systematic uncertainties of both measurements, we estimate the
parameter region of (\theta_13, \delta) in which the mass hierarchy can be
determined. If \theta_13 is relatively large, sin^2 2\theta_13 \gsim 0.05, and
both of \Delta m^2(ee) and \Delta m^2(\mu \mu) can be measured with the
precision of \sim 0.5 % it is possible to determine the neutrino mass hierarchy
at > 95% CL for 0.3 \pi \lsim \delta \lsim 1.7 \pi for the current best fit
values of all the other oscillation parameters.Comment: 12 pages, 6 postscript figure
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