418 research outputs found
Abelian family symmetries and the simplest models that give theta13=0 in the neutrino mixing matrix
I construct predictive models of neutrino mass and mixing that have fewer
parameters, both in the lepton sector and overall, than the default seesaw
model. The predictions are theta13=0 and one massless neutrino, with the models
having a Z4 or Z2 symmetry and just one extra degree of freedom: one real
singlet Higgs field. It has been shown that models with an unbroken family
symmetry, and with no Higgs fields other than the Standard Model Higgs doublet
produce masses and mixing matrices that have been ruled out by experiment.
Therefore, this article investigates the predictions of models with Abelian
family symmetries that involve Higgs singlets, doublets and triplets, in the
hope that they may produce the maximal and minimal mixing angles seen in the
best fit neutrino mixing matrix. I demonstrate that these models can only
produce mixing angles that are zero, maximal or unconfined by the symmetry. The
maximal mixing angles do not correspond to physical mixing, so an Abelian
symmetry can, at best, ensure that theta13=0, while leaving the solar and
atmospheric mixing angles as free parameters. To generate more features of the
best-fit mixing matrix a model with a non-Abelian symmetry and a complicated
Higgs sector would have to be used.Comment: 16 pages, no figure
Beta decay of 115-In to the first excited level of 115-Sn: Potential outcome for neutrino mass
Recent observation of beta decay of 115-In to the first excited level of
115-Sn with an extremely low Q_beta value (Q_beta ~ 1 keV) could be used to set
a limit on neutrino mass. To give restriction potentially competitive with
those extracted from experiments with 3-H (~2 eV) and 187-Re (~15 eV), atomic
mass difference between 115-In and 115-Sn and energy of the first 115-Sn level
should be remeasured with higher accuracy (possibly of the order of ~1 eV).Comment: 9 pages, 3 figures; talk at the NANP'05 Conferenc
Performances and stability of a 2.4 ton Gd organic liquid scintillator target for antineutrino detection
In this work we report the performances and the chemical and physical
properties of a (2 x 1.2) ton organic liquid scintillator target doped with Gd
up to ~0.1%, and the results of a 2 year long stability survey. In particular
we have monitored the amount of both Gd and primary fluor actually in solution,
the optical and fluorescent properties of the Gd-doped liquid scintillator
(GdLS) and its performances as a neutron detector, namely neutron capture
efficiency and average capture time. The experimental survey is ongoing, the
target being continuously monitored. After two years from the doping time the
performances of the Gd-doped liquid scintillator do not show any hint of
degradation and instability; this conclusion comes both from the laboratory
measurements and from the "in-tank" measurements. This is the largest stable
Gd-doped organic liquid scintillator target ever produced and continuously
operated for a long period
Searches for neutrinoless double beta decay
Neutrinoless double beta decay is a lepton number violating process whose
observation would also establish that neutrinos are their own anti-particles.
There are many experimental efforts with a variety of techniques. Some (EXO,
Kamland-Zen, GERDA phase I and CANDLES) started take data in 2011 and EXO has
reported the first measurement of the half life for the double beta decay with
two neutrinos of Xe. The sensitivities of the different proposals are
reviewed.Comment: 8 pages, prepared for TAUP 201
Searches for neutrinoless double beta decay
Neutrinoless double beta decay is a lepton number violating process whose
observation would also establish that neutrinos are their own anti-particles.
There are many experimental efforts with a variety of techniques. Some (EXO,
Kamland-Zen, GERDA phase I and CANDLES) started take data in 2011 and EXO has
reported the first measurement of the half life for the double beta decay with
two neutrinos of Xe. The sensitivities of the different proposals are
reviewed.Comment: 8 pages, prepared for TAUP 201
Searches for neutrinoless double beta decay
Neutrinoless double beta decay is a lepton number violating process whose
observation would also establish that neutrinos are their own anti-particles.
There are many experimental efforts with a variety of techniques. Some (EXO,
Kamland-Zen, GERDA phase I and CANDLES) started take data in 2011 and EXO has
reported the first measurement of the half life for the double beta decay with
two neutrinos of Xe. The sensitivities of the different proposals are
reviewed.Comment: 8 pages, prepared for TAUP 201
A New 76Ge Double Beta Decay Experiment at LNGS
This Letter of Intent has been submitted to the Scientific Committee of the
INFN Laboratori Nazionali del Gran Sasso (LNGS) in March 2004. It describes a
novel facility at the LNGS to study the double beta decay of 76Ge using an
(optionally active) cryogenic fluid shield. The setup will allow to scrutinize
with high significance on a short time scale the current evidence for
neutrinoless double beta decay of 76Ge using the existing 76Ge diodes from the
previous Heidelberg-Moscow and IGEX experiments. An increase in the lifetime
limit can be achieved by adding more enriched detectors, remaining thereby
background-free up to a few 100 kg-years of exposure.Comment: 67 pages, 19 eps figures, 17 tables, gzipped tar fil
The BNO-LNGS joint measurement of the solar neutrino capture rate in 71Ga
We describe a cooperative measurement of the capture rate of solar neutrinos
by the reaction 71Ga(\nu_e,e^-)71Ge. Extractions were made from a portion of
the gallium target in the Russian-American Gallium Experiment SAGE and the
extraction samples were transported to the Gran Sasso laboratory for synthesis
and counting at the Gallium Neutrino Observatory GNO. Six extractions of this
type were made and the resultant solar neutrino capture rate was 64
^{+24}_{-22} SNU, which agrees well with the overall result of the gallium
experiments. The major purpose of this experiment was to make it possible for
SAGE to continue their regular schedule of monthly solar neutrino extractions
without interruption while a separate experiment was underway to measure the
response of 71Ga to neutrinos from an 37Ar source. As side benefits, this
experiment proved the feasibility of long-distance sample transport in ultralow
background radiochemical experiments and familiarized each group with the
methods and techniques of the other.Comment: 7 pages, no figures; minor additions in version
Theoretical Prospects of Neutrinoless Double Beta Decay
The compelling experimental evidences for oscillations of solar and
atmospheric neutrinos imply the existence of 3-neutrino mixing in vacuum. We
briefly review the phenomenology of 3-neutrino mixing, and the current data on
the 3-neutrino mixing parameters. The open questions and the main goals of
future research in the field of neutrino mixing and oscillations are outlined.
The predictions for the effective Majorana mass || in neutrinoless double
beta (bb0nu-) decay in the case of 3-neutrino mixing and massive Majorana
neutrinos are reviewed. The physics potential of the experiments, searching for
bb0nu-decay and having sensitivity approximately 10 times better than the
presently reached, for providing information on the type of the neutrino mass
spectrum, on the absolute scale of neutrino masses and on the Majorana
CP-violation phases in the PMNS neutrino mixing matrix, is discussed.Comment: 15 pages, 2 postscript figures, LATEX; Invited talk given at the
Nobel Symposium (N 129) on Neutrino Physics, August 19 - 24, 2004, Haga
Slott, Enkoping, Swede
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