57 research outputs found
From Cuoricino to CUORE: investigating the inverted hierarchy region of neutrino mass
Cuoricino is a Double Beta Decay experiment operating deep underground, in the Laboratori Nazionali del Gran Sasso, Italy; at a depth of about 3500 m.w.e. The search for the 0νββ of 130Te is carried out with the bolometric technique and an upper limit of 3×1024 y (@ 90%C.L.) is set for this process. Cuoricino represents not only the most sensitive DBD Experiment presently operating but also a prototype for a next generation experiment, CUORE (Cryogenic Underground Observatory for Rare Events). The expected performance and sensitivity, based on Monte Carlo simulations and extrapolations of the present Cuoricino results, indicate that CUORE will be able to test the 0.02-0.05 eV region for the effective neutrino mass, having a high discovery potential in the inverted hierarchy region of the neutrino mass pattern
Experimental Status of Neutrino Physics
After a fascinating phase of discoveries, neutrino physics still has a few
mysteries such as the absolute mass scale, the mass hierarchy, the existence of
CP violation in the lepton sector and the existence of right-handed neutrinos.
It is also entering a phase of precision measurements. This is what motivates
the NUFACT 11 conference which prepares the future of long baseline neutrino
experiments. In this paper, we report the status of experimental neutrino
physics. We focus mainly on absolute mass measurements, oscillation parameters
and future plans for oscillation experiments
Discovery potential of xenon-based neutrinoless double beta decay experiments in light of small angular scale CMB observations
The South Pole Telescope (SPT) has probed an expanded angular range of the CMB temperature power spectrum. Their recent analysis of the latest cosmological data prefers nonzero neutrino masses, mnu = 0.32+-0.11 eV. This result, if confirmed by the upcoming Planck data, has deep implications on the discovery of the nature of neutrinos. In particular, the values of the effective neutrino mass involved in neutrinoless double beta decay (bb0nu) are severely constrained for both the direct and inverse hierarchy, making a discovery much more likely. In this paper, we focus in xenon-based bb0nu experiments, on the double grounds of their good performance and the suitability of the technology to large-mass scaling. We show that the current generation, with effective masses in the range of 100 kg and conceivable exposures in the range of 500 kg year, could already have a sizable opportunity to observe bb0nu events, and their combined discovery potential is quite large. The next generation, with an exposure in the range of 10 ton year, would have a much more enhanced sensitivity, in particular due to the very low specific background that all the xenon technologies (liquid xenon, high-pressure xenon and xenon dissolved in liquid scintillator) can achieve. In addition, a high-pressure xenon gas TPC also features superb energy resolution. We show that such detector can fully explore the range of allowed effective Majorana masses, thus making a discovery very likely
Relic neutrino masses and the highest energy cosmic rays
We consider the possibility that a large fraction of the ultrahigh energy
cosmic rays are decay products of Z bosons which were produced in the
scattering of ultrahigh energy cosmic neutrinos on cosmological relic
neutrinos. We compare the observed ultrahigh energy cosmic ray spectrum with
the one predicted in the above Z-burst scenario and determine the required mass
of the heaviest relic neutrino as well as the necessary ultrahigh energy cosmic
neutrino flux via a maximum likelihood analysis. We show that the value of the
neutrino mass obtained in this way is fairly robust against variations in
presently unknown quantities, like the amount of neutrino clustering, the
universal radio background, and the extragalactic magnetic field, within their
anticipated uncertainties. Much stronger systematics arises from different
possible assumptions about the diffuse background of ordinary cosmic rays from
unresolved astrophysical sources. In the most plausible case that these
ordinary cosmic rays are protons of extragalactic origin, one is lead to a
required neutrino mass in the range 0.08 eV - 1.3 eV at the 68 % confidence
level. This range narrows down considerably if a particular universal radio
background is assumed, e.g. to 0.08 eV - 0.40 eV for a large one. The required
flux of ultrahigh energy cosmic neutrinos near the resonant energy should be
detected in the near future by AMANDA, RICE, and the Pierre Auger Observatory,
otherwise the Z-burst scenario will be ruled out.Comment: 19 pages, 22 figures, REVTeX
S4 Flavor Symmetry and Fermion Masses: Towards a Grand Unified theory of Flavor
Pursuing a bottom-up approach to explore which flavor symmetry could serve as
an explanation of the observed fermion masses and mixings, we discuss an
extension of the standard model (SM) where the flavor structure for both quarks
and leptons is determined by a spontaneously broken S4 and the requirement that
its particle content is embeddable simultaneously into the conventional SO(10)
grand unified theory (GUT) and a continuous flavor symmetry G_f like SO(3)_f or
SU(3)_f. We explicitly provide the Yukawa and the Higgs sector of the model and
show its viability in two numerical examples which arise as small deviations
from rank one matrices. In the first case, the corresponding mass matrix is
democratic and in the second one only its 2-3 block is non-vanishing. We
demonstrate that the Higgs potential allows for the appropriate vacuum
expectation value (VEV) configurations in both cases, if CP is conserved. For
the first case, the chosen Yukawa couplings can be made natural by invoking an
auxiliary Z2 symmetry. The numerical study we perform shows that the best-fit
values for the lepton mixing angles theta_12 and theta_23 can be accommodated
for normal neutrino mass hierarchy. The results for the quark mixing angles
turn out to be too small. Furthermore the CP-violating phase delta can only be
reproduced correctly in one of the examples. The small mixing angle values are
likely to be brought into the experimentally allowed ranges by including
radiative corrections. Interestingly, due to the S4 symmetry the mass matrix of
the right-handed neutrinos is proportional to the unit matrix.Comment: 27 pages, published version with minor change
Theory of neutrinoless double beta decay
Neutrinoless double beta decay, which is a very old and yet elusive process,
is reviewed. Its observation will signal that lepton number is not conserved
and the neutrinos are Majorana particles. More importantly it is our best hope
for determining the absolute neutrino mass scale at the level of a few tens of
meV. To achieve the last goal certain hurdles have to be overcome involving
particle, nuclear and experimental physics. Nuclear physics is important for
extracting the useful information from the data. One must accurately evaluate
the relevant nuclear matrix elements, a formidable task. To this end, we review
the sophisticated nuclear structure approaches recently been developed, which
give confidence that the needed nuclear matrix elements can be reliably
calculated. From an experimental point of view it is challenging, since the
life times are long and one has to fight against formidable backgrounds. If a
signal is found, it will be a tremendous accomplishment. Then, of course, the
real task is going to be the extraction of the neutrino mass from the
observations. This is not trivial, since current particle models predict the
presence of many mechanisms other than the neutrino mass, which may contribute
or even dominate this process. We will, in particular, consider the following
processes: (i)The neutrino induced, but neutrino mass independent contribution.
(ii)Heavy left and/or right handed neutrino mass contributions.
(iii)Intermediate scalars (doubly charged etc). (iv)Supersymmetric (SUSY)
contributions. We will show that it is possible to disentangle the various
mechanisms and unambiguously extract the important neutrino mass scale, if all
the signatures of the reaction are searched in a sufficient number of nuclear
isotopes.Comment: 104 pages, 6 tables, 25 figures.References added. To appear in ROP
(Reports on Progress in Physics), copyright RO
A See-Saw model for fermion masses and mixings
We present a supersymmetric see-saw model giving rise to the most
general neutrino mass matrix compatible with Tri-Bimaximal mixing. We adopt the
flavour symmetry, broken by suitable vacuum expectation values
of a small number of flavon fields. We show that the vacuum alignment is a
natural solution of the most general superpotential allowed by the flavour
symmetry, without introducing any soft breaking terms. In the charged lepton
sector, mass hierarchies are controlled by the spontaneous breaking of the
flavour symmetry caused by the vevs of one doublet and one triplet flavon
fields instead of using the Froggatt-Nielsen U(1) mechanism. The next to
leading order corrections to both charged lepton mass matrix and flavon vevs
generate corrections to the mixing angles as large as .
Applied to the quark sector, the symmetry group can give a
leading order proportional to the identity as well as a matrix with
coefficients in the Cabibbo submatrix. Higher order
corrections produce non vanishing entries in the other entries which
are generically of .Comment: 30 pages, 3 figures, minor changes to match the published versio
High sensitivity GEM experiment on double beta decay of 76-Ge
The GEM project is designed for the next generation 2 beta decay experiments
with 76-Ge. One ton of ''naked'' HP Ge detectors (natural at the first GEM-I
phase and enriched in 76-Ge to 86% at the second GEM-II stage) are operating in
super-high purity liquid nitrogen contained in the Cu vacuum cryostat (sphere
with diameter 5 m). The latest is placed in the water shield. Monte Carlo
simulation evidently shows that sensitivity of the experiment (in terms of the
T1/2 limit for neutrinoless 2 beta decay) is 10^27 yr with natural HP Ge
crystals and 10^28 yr with enriched ones. These bounds corresponds to the
restrictions on the neutrino mass less than 0.05 eV and 0.015 eV with natural
and enriched detectors, respectively. Besides, the GEM-I set up could advance
the current best limits on the existence of neutralinos - as dark matter
candidates - by three order of magnitudes, and at the same time would be able
to identify unambiguously the dark matter signal by detection of its seasonal
modulation.Comment: LaTeX, 20 pages, 4 figure
Revisiting Bimaximal Neutrino Mixing in a Model with S4 Discrete Symmetry
In view of the fact that the data on neutrino mixing are still compatible
with a situation where Bimaximal mixing is valid in first approximation and it
is then corrected by terms of order of the Cabibbo angle, arising from the
diagonalization of the charged lepton masses, we construct a model based on the
discrete group S4 where those properties are naturally realized. The model is
supersymmetric in 4-dimensions and the complete flavour group is S4 x Z4 x
U(1)_FN, which also allows to reproduce the hierarchy of the charged lepton
spectrum. The only fine tuning needed in the model is to reproduce the small
observed value of r, the ratio between the neutrino mass squared differences.
Once the relevant parameters are set to accommodate r then the spectrum of
light neutrinos shows a moderate normal hierarchy and is compatible, within
large ambiguities, with the constraints from leptogenesis as an explanation of
the baryon asymmetry in the Universe.Comment: 30 pages, 5 figures; added reference
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