342 research outputs found
Probing the neutrino mass ordering with KM3NeT-ORCA: Analysis and perspectives
The discrimination of the two possible options for the neutrino mass ordering
(normal or inverted) is a major goal for current and future neutrino
oscillation experiments. Such goal might be reached by observing
high-statistics energy-angle spectra of events induced by atmospheric neutrinos
and antineutrinos propagating in the Earth matter. Large volume water-Cherenkov
detectors envisaged to this purpose include the so-called KM3NeT-ORCA project
(in seawater) and the IceCube-PINGU project (in ice). Building upon a previous
work focused on PINGU, we study in detail the effects of various systematic
uncertainties on the ORCA sensitivity to the mass ordering, for the reference
configuration with 9 m vertical spacing. We point out the need to control
spectral shape uncertainties at the percent level, the effects of better priors
on the theta-23 mixing parameter, and the benefits of an improved flavor
identification in reconstructed ORCA events.Comment: 15 pages, including 7 figures. A few paragraphs and references added.
Invited contribution to appear in the JPG Focus Issue on "Neutrino Mass and
Mass Ordering
Neutrinos self interactions in Supernovae
Oscillations of neutrino emerging from a supernova core are studied. In this
extremely high density region neutrino self interactions induce collective
flavor transitions. When collective transitions are decoupled from matter
oscillations, as for our chosen matter profile, an analytical interpretation of
the collective effects is possible, by means of a mechanical analogy with a
spherical pendulum. For inverted neutrino hierarchy the neutrino propagation
can be divided in three regimes: synchronization, bipolar oscillations, and
spectral split. Our simulation shows that averaging over neutrino trajectories
does not alter the nature of these three regimes.Comment: 6 pages, 7 figures, to appear in the Proceedings of the 43rd
Rencontres de Moriond EW session, La Thuile, Italy, 1-8 March 200
Neutrino Mass Hierarchy and Neutrino Oscillation Parameters with One Hundred Thousand Reactor Events
Abstract High-statistics reactor neutrino experiments at medium baselines will probe mass-mixing parameters governing neutrino oscillations at long wavelength, driven by the ( δm 2 , θ 12 ) and at short wavelength, driven by (Δ m 2 , θ 13 ).The interference between these two oscillations will allow to probe the mass hierarchy. The determination of the neutrino mass spectrum hierarchy, however, will require an unprecedented level of detector performance and collected statistics, and the control of several systematics at (sub)percent level. In this work we perform accurate theoretical calculations of reactor event spectra and refined statistical analyses to show that with O (10 5 ) reactor events, a typical sensitivity of ∼ 2 σ could be achieved by an experiment such as JUNO. We also show the impact of the energy scale and spectrum shape systematics on the determination of the hierarchy
Global constraints on absolute neutrino masses and their ordering
Within the standard three-neutrino framework, the absolute neutrino masses
and their ordering (either normal, NO, or inverted, IO) are currently unknown.
However, the combination of current data coming from oscillation experiments,
neutrinoless double beta decay searches, and cosmological surveys, can provide
interesting constraints for such unknowns in the sub-eV mass range, down to
O(0.1) eV in some cases. We discuss current limits on absolute neutrino mass
observables by performing a global data analysis, that includes the latest
results from oscillation experiments, neutrinoless double beta decay bounds
from the KamLAND-Zen experiment, and constraints from representative
combinations of Planck measurements and other cosmological data sets. In
general, NO appears to be somewhat favored with respect to IO at the level of
~2 sigma, mainly by neutrino oscillation data (especially atmospheric),
corroborated by cosmological data in some cases. Detailed constraints are
obtained via the chi^2 method, by expanding the parameter space either around
separate minima in NO and IO, or around the absolute minimum in any ordering.
Implications for upcoming oscillation and non-oscillation neutrino experiments,
including beta-decay searches, are also discussed.Comment: 17 pages, including 3 tables and 11 figure
Fast flavor conversions of supernova neutrinos: Classifying instabilities via dispersion relations
Supernova neutrinos can exhibit a rich variety of flavor conversion
mechanisms. In particular, they can experience "fast" self-induced flavor
conversions almost immediately above the core. Very recently, a novel method
has been proposed to investigate these phenomena, in terms of the dispersion
relation for the complex frequency and wave number (,) of
disturbances in the mean field of the flavor coherence. We discuss
a systematic approach to such instabilities, originally developed in the
context of plasma physics, and based of the time-asymptotic behavior of the
Green's function of the system. Instabilities are typically seen to emerge for
complex , and can be further characterized as convective (moving away
faster than they spread) and absolute (growing locally), depending on
-dependent features. Stable cases emerge when (but not ) is
complex, leading to disturbances damped in space, or when both and
are real, corresponding to complete stability. The analytical classification of
both unstable and stable modes leads not only to qualitative insights about
their features but also to quantitative predictions about the growth rates of
instabilities. Representative numerical solutions are discussed in a simple
two-beam model of interacting neutrinos. As an application, we argue that
supernova and binary neutron star mergers exhibiting a "crossing" in the
electron lepton number would lead to an absolute instability in the flavor
content of the neutrino gas.Comment: (v2, revised version: 25 pages, 15 pdf figures. Minor changes.
Figures improved. Matches the version published on PRD
Majorana neutrino mass constraints in the landscape of nuclear matrix elements
We discuss up-to-date constraints on the Majorana neutrino mass
from neutrinoless double beta decay ()
searches in experiments using different isotopes: KamLAND-Zen and EXO
(Xe), GERDA and MAJORANA (Ge) and CUORE (Te). Best fits
and upper bounds on are explored in the general landscape of
nuclear matrix elements (NME), as well as for specific NME values obtained in
representative nuclear models. By approximating the likelihood of
signals through quadratic forms, the analysis of separate and
combined isotope data becomes exceedingly simple, and allows to clarify various
aspects of multi-isotope data combinations. In particular, we analyze the
relative impact of different data in setting upper bounds on ,
as well as the conditions leading to nonzero at best fit, for
variable values of the NMEs. Detailed results on from various
combinations of data are reported in graphical and numerical form. Implications
for future data analyses and NME calculations are briefly
discussed.Comment: 13 pages, including 6 tables and 7 figure
Global 3ν oscillation analysis: Status of unknown parameters and future systematic challenges for ORCA and PINGU
Within the standard 3ν oscillation framework, we illustrate the status of currently unknown oscillation parameters: the θ23 octant, the mass hierarchy (normal or inverted), and the possible CP-violating phase δ, as derived by a (preliminary) global analysis of oscillation data available in 2015. We then discuss some challenges that will be faced by future, high-statistics analyses of spectral data, starting with one-dimensional energy spectra in reactor experiments, and concluding with two-dimensional energy-angle spectra in large-volume atmospheric experiments. It is shown that systematic uncertainties in the spectral shapes can noticeably affect the prospective sensitivities to unknown oscillation parameters, in particular to the mass hierarchy
Interplay between non-interfering neutrino exchange mechanisms and nuclear matrix elements in decay
We revisit the phenomenology of neutrinoless double beta ()
decay mediated by non-interfering exchange of light and heavy Majorana
neutrinos, in the context of current and prospective ton-scale experimental
searches, as well as of recent calculations of nuclear matrix elements (NME) in
different nuclear models. We derive joint upper bounds on the light and heavy
contributions to decay, for different sets of NME, through
separate and combined data coming from the following experiments (and
isotopes): KamLAND-Zen and EXO (Xe), GERDA, and MAJORANA (Ge) and CUORE (Te).
We further consider three proposed projects that could provide, within current
bounds, possible decay signals at level with an
exposure of 10 ton years: nEXO (Xe), LEGEND (Ge) and CUPID (Mo). Separate and
combined (Xe, Ge, Mo) signals are studied for different representative cases
and NME sets, and the conditions leading to (non)degenerate light and heavy
neutrino mechanisms are discussed. In particular, the role of heavy-to-light
NME ratios in different isotopes is highlighted through appropriate graphical
representations. By using different sets of ``true'' and ``test'' NME as a
proxy for nuclear uncertainties, it is shown that the relative contributions of
light and heavy neutrino exchange to signals may be
significantly biased in some cases. Implications for theoretical models
connecting light and heavy Majorana neutrino masses are also briefly
illustrated. These results provide further motivations to improve NME
calculations, so as to better exploit the physics potential of future
multi-isotope searches at the ton scale.Comment: 20 pages, 9 figure
Study of Cd -decay spectrum and quenching using spectral moments
We present an alternative analysis of the Cd -decay electron
energy spectrum in terms of spectral moments , corresponding to the
averaged values of powers of the particle energy. The
zeroth moment is related to the decay rate, while higher moments
are related to the spectrum shape. The here advocated spectral-moment
method (SMM) allows for a complementary understanding of previous results,
obtained using the so-called spectrum-shape method (SSM) and its revised
version, in terms of two free parameters: (the ratio of
axial-vector to vector couplings) and (the small vector-like relativistic
nuclear matrix element, -NME). We present numerical results for three
different nuclear models with the conserved vector current hypothesis (CVC)
assumption of . We show that most of the spectral information can
be captured by the first few moments which are simple quadratic forms (conic
sections) in the plane: an ellipse for and hyperbolae for
, all being nearly degenerate as a result of cancellations among
nuclear matrix elements. The intersections of these curves, as obtained by
equating theoretical and experimental values of , identify the favored
values of at a glance, without performing detailed fits. In
particular, we find that values around and are
consistently favored in each nuclear model, confirming the evidence for quenching in Cd, and shedding light on the role of the -NME. We
briefly discuss future applications of the SMM to other forbidden -decay
spectra sensitive to .Comment: 13 pages, including 5 figures and 2 table
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