170 research outputs found
Testing neutrino spectra formation in collapsing stars with the diffuse supernova neutrino flux
I address the question of what can be learned from the observation of the
diffuse supernova neutrino flux in the precision phase, at next generation
detectors of Megaton scale. An analytical study of the spectrum of the diffuse
flux shows that, above realistic detection thresholds of 10 MeV or higher, the
spectrum essentially reflects the exponential-times-polynomial structure of the
original neutrino spectrum at the emission point. There is only a weak (tens of
per cent) dependence on the power \beta describing the growth of the supernova
rate with the redshift. Different original neutrino spectra correspond to large
differences in the observed spectrum of events at a water Cerenkov detector:
for typical supernova rates, the ratio of the numbers of events in the first
and second energy bins (of 5 MeV width) varies in the interval 1.5 - 4.3 for
pure water (energy threshold 18 MeV) and in the range 1 - 2.5 for water with
Gadolinium (10 MeV threshold). In the first case discrimination would be
difficult due to the large errors associated with background. With Gadolinium,
instead, the reduction of the total error down to 10-20 % level would allow
spectral sensitivity, with a dramatic improvement of precision with respect to
the SN1987A data. Even in this latter case, for typical neutrino luminosity the
dependence on \beta is below sensitivity, so that it can be safely neglected in
data analysis.Comment: LaTeX, 10 pages, 5 figures; details added to fig. 5 and related text,
minor modifications to the text, references added. Version in press in
Phys.Rev.D
Revealing local failed supernovae with neutrino telescopes
We study the detectability of neutrino bursts from nearby direct black
hole-forming collapses (failed supernovae) at Megaton detectors. Due to their
high energetics, these bursts could be identified - by the time coincidence of
N >= 2 or N >= 3 events within a ~ 1 s time window - from as far as ~ 4-5 Mpc
away. This distance encloses several supernova-rich galaxies, so that failed
supernova bursts could be detected at a rate of up to one per decade,
comparable to the expected rate of the more common, but less energetic, neutron
star-forming collapses. Thus, the detection of a failed supernova within the
lifetime of a Mt detector is realistic. It might give the first evidence of
direct black hole formation, with important implications on the physics of this
phenomenon.Comment: LaTeX, 4 pages, 4 figures; minor changes to the text, results
unchange
Characterizing a supernova's Standing Accretion Shock Instability with neutrinos and gravitational waves
We perform a novel multi-messenger analysis for the identification and
parameter estimation of the Standing Accretion Shock Instability (SASI) in a
core collapse supernova with neutrino and gravitational wave (GW) signals. In
the neutrino channel, this method performs a likelihood ratio test for the
presence of SASI in the frequency domain. For gravitational wave signals we
process an event with a modified constrained likelihood method. Using simulated
supernova signals, the properties of the Hyper-Kamiokande neutrino detector,
and O3 LIGO Interferometric data, we produce the two-dimensional probability
density function (PDF) of the SASI activity indicator and calculate the
probability of detection as well as the false identification
probability . We discuss the probability to establish the
presence of the SASI as a function of the source distance in each observational
channel, as well as jointly. Compared to a single-messenger approach, the joint
analysis results in (at ) of SASI activities
that is larger by up to for a distance to the supernova of 5
kpc. We also discuss how accurately the frequency and duration of the SASI
activity can be estimated in each channel separately. Our methodology is
suitable for implementation in a realistic data analysis and a multi-messenger
setting.Comment: 24 pages, 15 figures, accepted by PR
Robustness and Reliability of Synergy-Based Myocontrol of a Multiple Degree of Freedom Robotic Arm
Neutrino Coherent Scattering Rates at Direct Dark Matter Detectors
Neutrino-induced recoil events may constitute a background to direct dark
matter searches, particularly for those detectors that strive to reach the
ton-scale and beyond. This paper discusses the expected neutrino-induced
background spectrum due to several of the most important sources, including
solar, atmospheric, and diffuse supernova neutrinos. The largest rate arises
from B produced solar neutrinos, providing upwards of events
per ton-year over all recoil energies for the heaviest nuclear targets. However
the majority of these B events are expected to be below the recoil
threshold of modern detectors. The remaining neutrino sources are found to
constitute a background to the WIMP-induced recoil rate only if the
WIMP-nucleon cross section is less than pb. Finally the sensitivity
to diffuse supernova neutrino flux for non-electron neutrino flavors is
discussed, and projected flux limits are compared with existing flux limits
Neutrino flavor conversion in a neutrino background: single- versus multi-particle description
In the early Universe, or near a supernova core, neutrino flavor evolution
may be affected by coherent neutrino-neutrino scattering. We develop a
microscopic picture of this phenomenon. We show that coherent scattering does
not lead to the formation of entangled states in the neutrino ensemble and
therefore the evolution of the system can always be described by a set of
one-particle equations. We also show that the previously accepted formalism
overcounts the neutrino interaction energy; the correct one-particle evolution
equations for both active-active and active-sterile oscillations contain
additional terms. These additional terms modify the index of refraction of the
neutrino medium, but have no effect on oscillation physics.Comment: 12 pages, 3 figures, minor typos correcte
Probing the neutrino mass hierarchy and the 13-mixing with supernovae
We consider in details the effects of the 13-mixing (sin^2 theta_{13}) and of
the type of mass hierarchy/ordering (sign[ Delta m^2_{13}]) on neutrino signals
from the gravitational collapses of stars. The observables (characteristics of
the energy spectra of nu_e and antinu_e events) sensitive to sin^2 theta_{13}
and sign[Delta m^2_{13}] have been calculated. They include the ratio of
average energies of the spectra, r_E = /, the ratio of widths of
the energy distributions, r_Gamma, the ratios of total numbers of nu_e and
antinu_e events at low energies, S, and in the high energy tails, R_{tail}. We
construct and analyze scatter plots which show the predictions for the
observables for different intervals of sin^2 theta_{13} and signs of Delta
m^2_{13}, taking into account uncertainties in the original neutrino spectra,
the star density profile, etc.. Regions in the space of observables r_E,
r_Gamma, S, R_{tail} exist in which certain mass hierarchy and intervals of
sin^2 theta_{13} can be identified or discriminated. We elaborate on the method
of the high energy tails in the spectra of events. The conditions are
formulated for which sin^2 theta_{13} can be (i) measured, (ii) restricted from
below, (iii) restricted from above. We comment on the possibility to determine
sin^2 theta_{13} using the time dependence of the signals due to the
propagation of the shock wave through the resonance layers of the star. We show
that the appearance of the delayed Earth matter effect in one of the channels
(nu_e or antinu_e) in combination with the undelayed effect in the other
channel will allow to identify the shock wave appeareance and determine the
mass hierarchy.Comment: LaTeX, 56 pages, 12 figures; a few clarifications added; typos
corrected. Version to appear in JCA
Supernova pointing with low- and high-energy neutrino detectors
A future galactic SN can be located several hours before the optical
explosion through the MeV-neutrino burst, exploiting the directionality of
--scattering in a water Cherenkov detector such as Super-Kamiokande. We
study the statistical efficiency of different methods for extracting the SN
direction and identify a simple approach that is nearly optimal, yet
independent of the exact SN neutrino spectra. We use this method to quantify
the increase in the pointing accuracy by the addition of gadolinium to water,
which tags neutrons from the inverse beta decay background. We also study the
dependence of the pointing accuracy on neutrino mixing scenarios and initial
spectra. We find that in the ``worst case'' scenario the pointing accuracy is
at 95% C.L. in the absence of tagging, which improves to
with a tagging efficiency of 95%. At a megaton detector, this accuracy can be
as good as . A TeV-neutrino burst is also expected to be emitted
contemporaneously with the SN optical explosion, which may locate the SN to
within a few tenths of a degree at a future km high-energy neutrino
telescope. If the SN is not seen in the electromagnetic spectrum, locating it
in the sky through neutrinos is crucial for identifying the Earth matter
effects on SN neutrino oscillations.Comment: 13 pages, 7 figures, Revtex4 format. The final version to be
published in Phys. Rev. D. A few points in the original text are clarifie
Supernova 1987A did not test the neutrino mass hierarchy
We dispel the misconception that data from SN 1987A favor the normal neutrino
mass hierarchy over the inverted hierarchy for \sin^2 \theta_{13} \gsim
10^{-4}. We find comparable fits for the two hierarchies. No bound can be
placed on the mixing angle even at the 1 level.Comment: 15 pages, 9 figure
Supernova neutrino oscillations: A simple analytical approach
Analyses of observable supernova neutrino oscillation effects require the
calculation of the electron (anti)neutrino survival probability P_ee along a
given supernova matter density profile. We propose a simple analytical
prescription for P_ee, based on a double-exponential form for the crossing
probability and on the concept of maximum violation of adiabaticity. In the
case of two-flavor transitions, the prescription is shown to reproduce
accurately, in the whole neutrino oscillation parameter space, the results of
exact numerical calculations for generic (realistic or power-law) profiles. The
analytical approach is then generalized to cover three-flavor transitions with
(direct or inverse) mass spectrum hierarchy, and to incorporate Earth matter
effects. Compact analytical expressions, explicitly showing the symmetry
properties of P_ee, are provided for practical calculations.Comment: 22 pages (RevTeX) + 5 figures (PostScript
- …