7,200 research outputs found
Overconstrained estimates of neutrinoless double beta decay within the QRPA
Estimates of nuclear matrix elements for neutrinoless double beta decay
(0nu2beta) based on the quasiparticle random phase approximations (QRPA) are
affected by theoretical uncertainties, which can be substantially reduced by
fixing the unknown strength parameter g_pp of the residual particle-particle
interaction through one experimental constraint - most notably through the
two-neutrino double beta decay (2nu2beta) lifetime. However, it has been noted
that the g_pp adjustment via 2\nu2\beta data may bring QRPA models in
disagreement with independent data on electron capture (EC) and single beta
decay (beta^-) lifetimes. Actually, in two nuclei of interest for 0nu2beta
decay (Mo-100 and Cd-116), for which all such data are available, we show that
the disagreement vanishes, provided that the axial vector coupling g_A is
treated as a free parameter, with allowance for g_A<1 (``strong quenching'').
Three independent lifetime data (2nu2beta, EC, \beta^-) are then accurately
reproduced by means of two free parameters (g_pp, g_A), resulting in an
overconstrained parameter space. In addition, the sign of the 2nu2beta matrix
element M^2nu is unambiguously selected (M^2nu>0) by the combination of all
data. We discuss quantitatively, in each of the two nuclei, these
phenomenological constraints and their consequences for QRPA estimates of the
0nu2beta matrix elements and of their uncertainties.Comment: Revised version (27 pages, including 10 figures), focussed on Mo-100
and Cd-116. To appear in J. Phys. G: Nucl. Phys. (2008
Formation of ultracold LiCs molecules
We present the first observation of ultracold LiCs molecules. The molecules
are formed in a two-species magneto-optical trap and detected by two-photon
ionization and time-of-flight mass spectrometry. The production rate
coefficient is found to be in the range 10^{-18}\unit{cm^3s^{-1}} to
10^{-16}\unit{cm^3s^{-1}}, at least an order of magnitude smaller than for
other heteronuclear diatomic molecules directly formed in a magneto-optical
trap.Comment: 8 pages, 2 figure
MSW mediated neutrino decay and the solar neutrino problem
We investigate the solar neutrino problem assuming simultaneous presence of
MSW transitions in the sun and neutrino decay on the way from sun to earth. We
do a global -analysis of the data on total rates in Cl, Ga and
Superkamiokande (SK) experiments and the SK day-night spectrum data and
determine the changes in the allowed region in the \dm - \tan^2\theta plane
in presence of decay. We also discuss the implications for unstable neutrinos
in the SNO experiment.Comment: Final version to appear in Phys. Rev.
Ground-state properties of tubelike flexible polymers
In this work we investigate structural properties of native states of a
simple model for short flexible homopolymers, where the steric influence of
monomeric side chains is effectively introduced by a thickness constraint. This
geometric constraint is implemented through the concept of the global radius of
curvature and affects the conformational topology of ground-state structures. A
systematic analysis allows for a thickness-dependent classification of the
dominant ground-state topologies. It turns out that helical structures,
strands, rings, and coils are natural, intrinsic geometries of such tubelike
objects
Reactor Neutrino Experiments Compared to Superbeams
We present a detailed quantitative discussion of the measurement of the
leptonic mixing angle with a future reactor neutrino
oscillation experiment consisting of a near and far detector. We perform a
thorough analysis of the impact of various systematical errors and compare the
resulting physics potential to the one of planned first-generation superbeam
experiments. Furthermore, we investigate the complementarity of both types of
experiments. We find that, under realistic assumptions, a determination of
down to is possible with reactor experiments.
They are thus highly competitive to first-generation superbeams and may be able
to test on shorter timescales. In addition, we find that
the combination of a KamLAND-size reactor experiment with one or two superbeams
could substantially improve the ability to access the neutrino mass hierarchy
or the leptonic CP phase.Comment: Typo in Eq. (9) corrected. 36 pages, 12 figure
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
Three-flavor solar neutrino oscillations with terrestrial neutrino constraints
We present an updated analysis of the current solar neutrino data in terms of
three-flavor oscillations, including the additional constraints coming from
terrestrial neutrino oscillation searches at the CHOOZ (reactor),
Super-Kamiokande (atmospheric), and KEK-to-Kamioka (accelerator) experiments.
The best fit is reached for the subcase of two-family mixing, and the
additional admixture with the third neutrino is severely limited. We discuss
the relevant features of the globally allowed regions in the oscillation
parameter space, as well as their impact on the amplitude of possible
CP-violation effects at future accelerator experiments and on the
reconstruction accuracy of the mass-mixing oscillation parameters at the
KamLAND reactor experiment.Comment: 10 pages + 8 figure
Three-generation flavor transitions and decays of supernova relic neutrinos
If neutrinos have mass, they can also decay. Decay lifetimes of cosmological
interest can be probed, in principle, through the detection of the redshifted,
diffuse neutrino flux produced by all past supernovae--the so-called supernova
relic neutrino (SRN) flux. In this work, we solve the SRN kinetic equations in
the general case of three-generation flavor transitions followed by invisible
(nonradiative) two-body decays. We then use the general solution to calculate
observable SRN spectra in some representative decay scenarios. It is shown
that, in the presence of decay, the SRN event rate can basically span the whole
range below the current experimental upper bound--a range accessible to future
experimental projects. Radiative SRN decays are also briefly discussed.Comment: 25 pages, including 7 figure
Confronting Spin Flavor Solutions of the Solar Neutrino Problem with current and future solar neutrino data
We show that spin flavor precession solutions to the solar neutrino problem,
although preferred by the latest solar data, are ruled out by the first results
from the KamLAND reactor experiment, at more than 3_sigma. An illustrative chi2
plot comparing these descriptions with oscillations is given.Comment: new appendix added discussing the impact of the KamLAND data. This
updates the one published in Phys.Rev.D66:093009,200
The atmospheric neutrino anomaly without maximal mixing?
We consider a pattern of neutrino masses in which there is an approximate
mass degeneracy between the two mass eigenstates most coupled to the
and flavour eigenstates. Earth-matter effects can lift this
degeneracy and induce an effectively maximal mixing between these two
generations. This occurs if 's contain comparable admixtures of the
degenerate eigenstates, even rather small ones. This provides an explanation of
the atmospheric neutrino anomaly in which the {\it ab initio} introduction of a
large mixing angle is not required. To test this possibility we perform a novel
and detailed analysis of the 52 kiloton-year SuperKamiokande data, and we find
that in a large region of parameter space the corresponding confidence levels
are excellent. The most recent results from the Chooz reactor experiment,
however, severely curtail this region, so that the conventional scenario with
nearly maximal mixing angles --which we also analyse in detail-- is supported
by the data.Comment: Some relevant references added and a misprint correcte
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