1,414 research outputs found
Neutrino mass hierarchy and precision physics with medium-baseline reactors: Impact of energy-scale and flux-shape uncertainties
Nuclear reactors provide intense sources of electron antineutrinos,
characterized by few-MeV energy E and unoscillated spectral shape Phi(E).
High-statistics observations of reactor neutrino oscillations over
medium-baseline distances L ~ O(50) km would provide unprecedented
opportunities to probe both the long-wavelength mass-mixing parameters (delta
m^2 and theta_12) and the short-wavelength ones (Delta m^2 and theta_13),
together with the subtle interference effects associated with the neutrino mass
hierarchy (either normal or inverted). In a given experimental setting - here
taken as in the JUNO project for definiteness - the achievable hierarchy
sensitivity and parameter accuracy depend not only on the accumulated
statistics but also on systematic uncertainties, which include (but are not
limited to) the mass-mixing priors and the normalizations of signals and
backgrounds. We examine, in addition, the effect of introducing smooth
deformations of the detector energy scale, E -> E'(E), and of the reactor flux
shape, Phi(E) -> Phi'(E), within reasonable error bands inspired by
state-of-the-art estimates. It turns out that energy-scale and flux-shape
systematics can noticeably affect the performance of a JUNO-like experiment,
both on the hierarchy discrimination and on precision oscillation physics. It
is shown that a significant reduction of the assumed energy-scale and
flux-shape uncertainties (by, say, a factor of 2) would be highly beneficial to
the physics program of medium-baseline reactor projects. Our results also shed
some light on the role of the inverse-beta decay threshold, of geoneutrino
backgrounds, and of matter effects in the analysis of future reactor
oscillation data.Comment: 13 pages, including 17 figures. Minor changes in the text, references
added. To appear in Phys. Rev.
Neutrino masses and mixings: Status of known and unknown parameters
Within the standard 3nu mass-mixing framework, we present an up-to-date
global analysis of neutrino oscillation data (as of January 2016), including
the latest available results from experiments with atmospheric neutrinos
(Super-Kamiokande and IceCube DeepCore), at accelerators (first T2K anti-nu and
NOvA nu runs in both appearance and disappearance mode), and at short-baseline
reactors (Daya Bay and RENO far/near spectral ratios), as well as a reanalysis
of older KamLAND data in the light of the "bump" feature recently observed in
reactor spectra. We discuss improved constraints on the five known oscillation
parameters (delta m^2, |Delta m^2|, sin^2theta_12, sin^2theta_13,
sin^2theta_23), and the status of the three remaining unknown parameters: the
mass hierarchy, the theta_23 octant, and the possible CP-violating phase delta.
With respect to previous global fits, we find that the reanalysis of KamLAND
data induces a slight decrease of both delta m^2 and sin^2theta_12, while the
latest accelerator and atmospheric data induce a slight increase of |Delta
m^2|. Concerning the unknown parameters, we confirm the previous intriguing
preference for negative values of sin(delta) [with best-fit values around
sin(delta) ~ -0.9], but we find no statistically significant indication about
the theta_23 octant or the mass hierarchy (normal or inverted). Assuming an
alternative (so-called LEM) analysis of NOvA data, some delta ranges can be
excluded at >3 sigma, and the normal mass hierarchy appears to be slightly
favored at 90% C.L. We also describe in detail the covariances of selected
pairs of oscillation parameters. Finally, we briefly discuss the implications
of the above results on the three non-oscillation observables sensitive to the
(unknown) absolute nu mass scale: the sum of nu masses, the effective nu_e
mass, and the effective Majorana mass.Comment: 15 pages, 9 figures, 2 tables. Invited contribution prepared for the
Nuclear Physics B Special Issue on "Neutrino Oscillations" celebrating the
Nobel Prize in Physics 201
Massive Quantum Memories by Periodically Inverted Dynamic Evolutions
We introduce a general scheme to realize perfect quantum state reconstruction
and storage in systems of interacting qubits. This novel approach is based on
the idea of controlling the residual interactions by suitable external controls
that, acting on the inter-qubit couplings, yield time-periodic inversions in
the dynamical evolution, thus cancelling exactly the effects of quantum state
diffusion. We illustrate the method for spin systems on closed rings with XY
residual interactions, showing that it enables the massive storage of
arbitrarily large numbers of local states, and we demonstrate its robustness
against several realistic sources of noise and imperfections.Comment: 10 pages, 3 figures. Contribution to the Proceedings of the Workshop
on "Quantum entanglement in physical and information sciences", held in Pisa,
December 14-18, 200
Status of three-neutrino oscillation parameters, circa 2013
The standard three-neutrino (3nu) oscillation framework is being increasingly
refined by results coming from different sets of experiments, using neutrinos
from solar, atmospheric, accelerator and reactor sources. At present, each of
the known oscillation parameters [the two squared mass gaps (delta m^2, Delta
m^2) and the three mixing angles (theta_12}, theta_13, theta_23)] is dominantly
determined by a single class of experiments. Conversely, the unknown parameters
[the mass hierarchy, the theta_23 octant and the CP-violating phase delta] can
be currently constrained only through a combined analysis of various
(eventually all) classes of experiments. In the light of recent new results
coming from reactor and accelerator experiments, and of their interplay with
solar and atmospheric data, we update the estimated N-sigma ranges of the known
3nu parameters, and revisit the status of the unknown ones. Concerning the
hierarchy, no significant difference emerges between normal and inverted mass
ordering. A slight overall preference is found for theta_23 in the first octant
and for nonzero CP violation with sin delta < 0; however, for both parameters,
such preference exceeds 1 sigma only for normal hierarchy. We also discuss the
correlations and stability of the oscillation parameters within different
combinations of data sets.Comment: Updated and revised version, accepted for publication in PRD. The
analysis includes the latest (March 2014) T2K disappearance data: all the
figures and the numerical results have been updated, and parts of the text
have been revised accordingl
Mantle geoneutrinos in KamLAND and Borexino
The KamLAND and Borexino experiments have observed, each at ~4 sigma level,
signals of electron antineutrinos produced in the decay chains of thorium and
uranium in the Earth's crust and mantle (Th and U geoneutrinos). Various pieces
of geochemical and geophysical information allow an estimation of the crustal
geoneutrino flux components with relatively small uncertainties. The mantle
component may then be inferred by subtracting the estimated crustal flux from
the measured total flux. To this purpose, we analyze in detail the experimental
Th and U geoneutrino event rates in KamLAND and Borexino, including neutrino
oscillation effects. We estimate the crustal flux at the two detector sites,
using state-of-the-art information about the Th and U distribution on global
and local scales. We find that crust-subtracted signals show hints of a
residual mantle component, emerging at ~2.4 sigma level by combining the
KamLAND and Borexino data. The inferred mantle flux slightly favors scenarios
with relatively high Th and U abundances, within +-1 sigma uncertainties
comparable to the spread of predictions from recent mantle models.Comment: Slight changes and improvements in the text & figures. Results
unchanged. To appear in Phys. Rev.
Current unknowns in the three-neutrino framework
We present an up-to-date global analysis of data coming from neutrino oscillation and non-oscillation experiments, as available in April 2018, within the standard framework including three massive and mixed neutrinos. We discuss in detail the status of the three-neutrino (3ν) mass-mixing parameters, both known and unknown. Concerning the latter, we find that: normal ordering (NO) is favored over inverted ordering (IO) at 3σ level; the Dirac CP phase is constrained within ∼15% (∼9%) uncertainty in NO (IO) around nearly-maximal CP-violating values; the octant of the largest mixing angle and the absolute neutrino masses remain undetermined. We briefly comment on other unknowns related to theoretical and experimental uncertainties (within 3ν) or possible new states and interactions (beyond 3ν)
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