1,930 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.
Four-neutrino oscillation solutions of the atmospheric neutrino anomaly
In the context of neutrino scenarios characterized by four (three active plus
one sterile) neutrino species and by mass spectra with two separated doublets,
we analyze solutions to the atmospheric neutrino anomaly which smoothly
interpolate between \nu_\mu-->\nu_\tau and \nu_\mu-->\nu_s oscillations. We
show that, although the Super-Kamiokande data disfavor the pure \nu_\mu-->\nu_s
channel, they do not exclude its occurrence, with sizable amplitude, in
addition to the \nu_\mu-->\nu_\tau channel. High energy muon data appear to be
crucial in assessing the relative amplitude of active and sterile neutrino
oscillations. It is also qualitatively shown that such atmospheric \nu
solutions are compatible with analogous solutions to the solar neutrino
problem, which involve oscillations of \nu_e in both sterile and active states.Comment: Added references. Accepted for publication in Phys. Rev.
Unbinned test of time-dependent signals in real-time neutrino oscillation experiments
Real-time neutrino oscillation experiments such as Super-Kamiokande (SK), the
Sudbury Neutrino Observatory (SNO), the Kamioka Liquid scintillator
Anti-Neutrino Detector (KamLAND), and Borexino, can detect time variations of
the neutrino signal, provided that the statistics is sufficiently high. We
quantify this statement by means of a simple unbinned test, whose sensitivity
depends on the variance of the signal in the time domain, as well as on the
total number of signal and background events. The test allows a unified
discussion of the statistical uncertainties affecting current or future
measurements of eccentricity-induced variations and of day-night asymmetries
(in SK, SNO, and Borexino), as well as of reactor power variations (in
KamLAND).Comment: 17 pages, including 3 figure
The Higgs Boson Mass from Precision Electroweak Data
We present a new global fit to precision electroweak data, including new low-
and high-energy data and analyzing the radiative corrections arising from the
minimal symmetry breaking sectors of the Standard Model (SM) and its
supersymmetric extension (MSSM). It is shown that present data favor a Higgs
mass of O(M_Z): M_H = 76+152-50 GeV. We confront our analysis with
(meta)stability and perturbative bounds on the SM Higgs mass, and the
theoretical upper bound on the MSSM Higgs mass. Present data do not
discriminate significantly between the SM and MSSM Higgs mass ranges. We
comment in passing on the sensitivity of the Higgs mass determination to the
values of alpha(M_Z) and alpha_s(M_Z).Comment: 10 pages, latex, 8 figures as uu-encoded postscript fil
Neutrino physics
A brief review of the status of neutrino masses and mixings is presented, with emphasis on Italian contributions to this field of research
Analysis of energy- and time-dependence of supernova shock effects on neutrino crossing probabilities
It has recently been realized that supernova neutrino signals may be affected
by shock propagation over a time interval of a few seconds after bounce. In the
standard three-neutrino oscillation scenario, such effects crucially depend on
the neutrino level crossing probability P_H in the 1-3 sector. By using a
simplified parametrization of the time-dependent supernova radial density
profile, we explicitly show that simple analytical expressions for P_H
accurately reproduce the phase-averaged results of numerical calculations in
the relevant parameter space. Such expressions are then used to study the
structure of P_H as a function of energy and time, with particular attention to
cases involving multiple crossing along the shock profile. Illustrative
applications are given in terms of positron spectra generated by supernova
electron antineutrinos through inverse beta decay.Comment: Major changes both in the text and in the figures in order to include
the effect of a step-like shock front density profile; final version to
appear in Physical Review
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