663 research outputs found
Resolving Neutrino Mass Hierarchy and CP Degeneracy by Two Identical Detectors with Different Baselines
We explore the possibility of simultaneous determination of neutrino mass
hierarchy and the CP violating phase by using two identical detectors placed at
different baseline distances. We focus on a possible experimental setup using
neutrino beam from J-PARC facility in Japan with beam power of 4MW and megaton
(Mton)-class water Cherenkov detectors, one placed in Kamioka and the other at
somewhere in Korea. We demonstrate, under reasonable assumptions of systematic
uncertainties, that the two-detector complex with each fiducial volume of 0.27
Mton has potential of resolving neutrino mass hierarchy up to sin^2 2theta_{13}
> 0.03 (0.055) at 2\sigma (3\sigma) CL for any values of delta and at the same
time has the sensitivity to CP violation by 4 + 4 years running of nu_e and
nu_e-bar appearance measurement. The significantly enhanced sensitivity is due
to clean detection of modulation of neutrino energy spectrum, which is enabled
by cancellation of systematic uncertainties between two identical detectors
which receive the neutrino beam with the same energy spectrum in the absence of
oscillations.Comment: 23 pages, 10 figures, version published in PR
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
On in situ Determination of Earth Matter Density in Neutrino Factory
We point out that an accurate in situ determination of the earth matter
density \rho is possible in neutrino factory by placing a detector at the magic
baseline, L = \sqrt{2} \pi / G_{F} N_{e} where N_{e} denotes electron number
density. The accuracy of matter density determination is excellent in a region
of relatively large theta_{13} with fractional uncertainty \delta \rho / \rho
of about 0.43%, 1.3%, and \lsim 3% at 1 sigma CL at sin^2 2theta_{13}=0.1,
10^{-2}, and 3 x 10^{-3}, respectively. At smaller theta_{13} the uncertainty
depends upon the CP phase delta, but it remains small, 3%-7% in more than 3/4
of the entire region of delta at sin^2 2theta_{13} = 10^{-4}. The results would
allow us to solve the problem of obscured CP violation due to the uncertainty
of earth matter density in a wide range of theta_{13} and delta. It may provide
a test for the geophysical model of the earth, or it may serve as a method for
stringent test of the MSW theory of neutrino propagation in matter once an
accurate geophysical estimation of the matter density is available.Comment: 21 pages, 4 figures, version to appear in PR
The Complementarity of Eastern and Western Hemisphere Long-Baseline Neutrino Oscillation Experiments
We present a general formalism for extracting information on the fundamental
parameters associated with neutrino masses and mixings from two or more long
baseline neutrino oscillation experiments. This formalism is then applied to
the current most likely experiments using neutrino beams from the Japan Hadron
Facility (JHF) and Fermilab's NuMI beamline. Different combinations of muon
neutrino or muon anti-neutrino running are considered. To extract the type of
neutrino mass hierarchy we make use of the matter effect. Contrary to naive
expectation, we find that both beams using neutrinos is more suitable for
determining the hierarchy provided that the neutrino energy divided by baseline
() for NuMI is smaller than or equal to that of JHF. Whereas to determine
the small mixing angle, , and the CP or T violating phase
, one neutrino and the other anti-neutrino is most suitable. We make
extensive use of bi-probability diagrams for both understanding and extracting
the physics involved in such comparisons.Comment: 21 pages, Latex, 3 postscript figure
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
Unity of CP and T Violation in Neutrino Oscillations
In a previous work a simultaneous P- CP[P] and P- T[P] bi-probability plot
was proposed as a useful tool for unified graphical description of CP and T
violation in neutrino oscillation. The ``baseball diamond'' structure of the
plot is understood as a consequence of the approximate CP-CP and the T-CP
relations obeyed by the oscillation probabilities. In this paper, we make a
step forward toward deeper understanding of the unified graphical
representation by showing that these two relations are identical in its
content, suggesting a truly unifying view of CP and T violation in neutrino
oscillations. We suspect that the unity reflects the underlying CPT theorem. We
also present calculation of corrections to the CP-CP and the T-CP relations to
leading order in Delta m^2_{21} / Delta m^2_{31} and s^2_{13}.Comment: 20 references added, version to appear in "Focus Issue on Neutrino
Physics" of New Journal of Physic
Perturbation Theory of Neutrino Oscillation with Nonstandard Neutrino Interactions
We discuss various physics aspects of neutrino oscillation with non-standard
interactions (NSI). We formulate a perturbative framework by taking \Delta
m^2_{21} / \Delta m^2_{31}, s_{13}, and the NSI elements \epsilon_{\alpha
\beta} (\alpha, \beta = e, \mu, \tau) as small expansion parameters of the same
order \epsilon. Within the \epsilon perturbation theory we obtain the S matrix
elements and the neutrino oscillation probability formula to second order
(third order in \nu_e related channels) in \epsilon. The formula allows us to
estimate size of the contribution of any particular NSI element
\epsilon_{\alpha beta} to the oscillation probability in arbitrary channels,
and gives a global bird-eye view of the neutrino oscillation phenomena with
NSI. Based on the second-order formula we discuss how all the conventional
lepton mixing as well as NSI parameters can be determined. Our results shows
that while \theta_{13}, \delta, and the NSI elements in \nu_e sector can in
principle be determined, complete measurement of the NSI parameters in the
\nu_\mu - \nu_\tau sector is not possible by the rate only analysis. The
discussion for parameter determination and the analysis based on the matter
perturbation theory indicate that the parameter degeneracy prevails with the
NSI parameters. In addition, a new solar-atmospheric variable exchange
degeneracy is found. Some general properties of neutrino oscillation with and
without NSI are also illuminated.Comment: manuscript restructured, discussion of new type of parameter
degeneracy added. 47 page
Clone flow analysis for a theory inspired Neutrino Experiment planning
The presence of several clone solutions in the simultaneous measurement of
() has been widely discussed in literature. In this letter
we write the analytical formulae of the clones location in the
() plane as a function of the physical input pair
(). We show how the clones move with changing
. The "clone flow" can be significantly different if computed
(naively) from the oscillation probabilities or (exactly) from the
probabilities integrated over the neutrino flux and cross-section.
Using our complete computation we compare the clone flow of a set of possible
future neutrino experiments: the CERN SuperBeam, BetaBeam and Neutrino Factory
proposals. We show that the combination of these specific BetaBeam and
SuperBeam does not help in solving the degeneracies. On the contrary, the
combination of one of them with the Neutrino Factory Golden and Silver channel
can be used, from a theoretical point of view, to solve completely the
eightfold degeneracy.Comment: 23 pages, using epsfi
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
Phenomenological Implications of a Class of Neutrino Mass Matrices
The generic predictions of two-texture zero neutrino mass matrices of class A
in the flavor basis have been reexamined especially in relation to the
degeneracy between mass matrices of types A_1 and A_2 and interesting
constraints on the neutrino parameters have been obtained. It is shown that the
octant of and the quadrant of the Dirac-type CP-violating phase
can be used to lift this degeneracy.Comment: 16 pages, 4 figures, final version with minor changes to appear in
Nucl. Phys.
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