831 research outputs found
Bounds on effective Majorana neutrino masses at HERA
The lepton-number violating process e p \to nu_e l l' X mediated by Majorana
neutrinos is studied for the HERA collider for (l l') = (e tau), (mu tau), (mu
mu) and (tau tau). Only the muonic decay of the tau is considered. The direct
limit on the effective muon Majorana mass, is improved
significantly to 4.0 times 10^3 GeV and for the first time direct limits on the
analogous effective masses connected with the tau sector are given, namely 4.2
times 10^3 GeV for , 4.4 times 10^3 GeV for and 2.0
times 10^4 GeV for . We find that a more general analysis for an
upgraded HERA could improve this values by a factor of up to 40, yet still
being orders of magnitude worse than indirect limits.Comment: 9 pages, 4 figures, revised versio
Neutrino physics with multi-ton scale liquid xenon detectors
We study the sensitivity of large-scale xenon detectors to low-energy solar
neutrinos, to coherent neutrino-nucleus scattering and to neutrinoless double
beta decay. As a concrete example, we consider the xenon part of the proposed
DARWIN (Dark Matter WIMP Search with Noble Liquids) experiment. We perform
detailed Monte Carlo simulations of the expected backgrounds, considering
realistic energy resolutions and thresholds in the detector. In a low-energy
window of 2-30 keV, where the sensitivity to solar pp and Be-neutrinos is
highest, an integrated pp-neutrino rate of 5900 events can be reached in a
fiducial mass of 14 tons of natural xenon, after 5 years of data. The
pp-neutrino flux could thus be measured with a statistical uncertainty around
1%, reaching the precision of solar model predictions. These low-energy solar
neutrinos will be the limiting background to the dark matter search channel for
WIMP-nucleon cross sections below 210 cm and WIMP
masses around 50 GeVc, for an assumed 99.5% rejection of
electronic recoils due to elastic neutrino-electron scatters. Nuclear recoils
from coherent scattering of solar neutrinos will limit the sensitivity to WIMP
masses below 6 GeVc to cross sections above
410cm. DARWIN could reach a competitive half-life
sensitivity of 5.610 y to the neutrinoless double beta decay of
Xe after 5 years of data, using 6 tons of natural xenon in the central
detector region.Comment: 17 pages, 4 figure
Gator: a low-background counting facility at the Gran Sasso Underground Laboratory
A low-background germanium spectrometer has been installed and is being
operated in an ultra-low background shield (the Gator facility) at the Gran
Sasso underground laboratory in Italy (LNGS). With an integrated rate of ~0.16
events/min in the energy range between 100-2700 keV, the background is
comparable to those of the world's most sensitive germanium detectors. After a
detailed description of the facility, its background sources as well as the
calibration and efficiency measurements are introduced. Two independent
analysis methods are described and compared using examples from selected sample
measurements. The Gator facility is used to screen materials for XENON, GERDA,
and in the context of next-generation astroparticle physics facilities such as
DARWIN.Comment: 14 pages, 6 figures, published versio
Improved bounds on SUSY accompanied neutrinoless double beta decay
Neutrinoless double beta decay induced by light Majorana neutrino exchange
between two decaying nucleons with squark/slepton exchange inside one and W
exchange inside the other nucleon (so-called vector-scalar exchange) gives
stringent limits on R-parity violating interactions. We have extended previous
work by including the tensor contribution to the transition rate. We discuss
the improved limits on trilinear \Rp -MSSM couplings imposed by the current
experimental limit on the \znbb decay half-life of Ge.Comment: replaced by revised version to appear in Phys. Lett.
A general parametrization for the long-range part of neutrinoless double beta decay
Double beta decay has been proven to be a powerful tool to constrain
violating physics beyond the standard model. We present a representation for
the long-range part of the general decay rate allowed by
Lorentz-invariance. Combined with the short range part this general
parametrization in terms of effective violating couplings will provide
the limits on arbitrary lepton number violating theories.Comment: Talk presented by H. P\"as at the Erice School on Nuclear Physics,
19th course "Neutrinos in Astro, Particle and Nuclear Physics", Erice, Italy,
16-24 September 1997, 2 pages, Latex, requires worldsci.st
Kaluza-Klein Dark Matter: Direct Detection vis-a-vis LHC
We explore the phenomenology of Kaluza-Klein (KK) dark matter in very general
models with universal extra dimensions (UEDs), emphasizing the complementarity
between high-energy colliders and dark matter direct detection experiments. In
models with relatively small mass splittings between the dark matter candidate
and the rest of the (colored) spectrum, the collider sensitivity is diminished,
but direct detection rates are enhanced. UEDs provide a natural framework for
such mass degeneracies. We consider both 5-dimensional and 6-dimensional
non-minimal UED models, and discuss the detection prospects for various KK dark
matter candidates: the KK photon , the KK -boson , the KK
Higgs boson and the spinless KK photon . We combine collider
limits such as electroweak precision data and expected LHC reach, with
cosmological constraints from WMAP, and the sensitivity of current or planned
direct detection experiments. Allowing for general mass splittings, we show
that neither colliders, nor direct detection experiments by themselves can
explore all of the relevant KK dark matter parameter space. Nevertheless, they
probe different parameter space regions, and the combination of the two types
of constraints can be quite powerful. For example, in the case of in
5D UEDs the relevant parameter space will be almost completely covered by the
combined LHC and direct detection sensitivities expected in the near future.Comment: 52 pages, 29 figure
A scheme for the extraction of WIMP-nucleon scattering cross sections from total event rates
We propose a scheme that allows to analytically determine the three
elementary cross sections and connect the solutions to the relative sign
between the proton and the neutron spin scattering amplitudes once the
measurements of total event rate from three appropriate targets become
available. In this way it is thus possible to extract the maximum information
on the supersymmetric parameter space obtainable from direct detection
experiments, in the case that the dark matter particle is the lightest
neutralino. Our scheme is based on suitably normalized form of the isospin
momentum dependent structure functions entering in the spin-dependent elastic
neutralino-nucleus cross section. We compare these functions with the commonly
used ones and discuss their advantages: in particular, these allow in the
spin-dependent cross section to factorize the particle physics degrees of
freedom from the momentum transfer dependent nuclear structure functions as it
happens in the spin-independent cross section with the nuclear form factor.Comment: 8 pages, 4 figures. Title, text and references revised and expanded.
Added an Appendix explaining the advantages of the normalized spin structure
functions. Accepted in PR
Bilinear R-parity violating SUSY: Neutrinoless double beta decay in the light of solar and atmospheric neutrino data
Neutrinoless double beta (\znbb) decay is considered within bilinear
R-parity breaking supersymmetry, including the full one-loop corrections to the
neutrino-neutralino mass matrix. Expected rates for \znbb decay in this model
are discussed in light of recent atmospheric and solar neutrino data. We
conclude that (a) tree-level calculations for \znbb decay within the bilinear
model are not reliable in the range of parameters preferred by current solar
and atmospheric neutrino problems. And (b) if the solar and atmospheric
neutrino problems are to be solved within bilinear R-parity violating SUSY the
expected rates for \znbb decay are very low; the effective Majorana neutrino
mass at most 0.01 eV and typical values being one order of magnitude lower.
Observing \znbb decay in the next round of experiments therefore would rule
out the bilinear R-parity violating supersymmetric model as an explanation for
solar and atmospheric neutrino oscillations, as well as any hierarchical scheme
for neutrino masses, unless new neutrino interactions are present.Comment: 1 reference added, enlarged discussion of loop
Hot and Cold Dark Matter Search with GENIUS
GENIUS is a proposal for a large volume detector to search for rare events. An array of 40-400 'naked' HPGe detectors will be operated in a tank filled with ultra-pure liquid nitrogen. After a description of performed technical studies of detector operation in liquid nitrogen and of Monte Carlo simulations of expected background components, the potential of GENIUS for detecting WIMP dark matter, the neutrinoless double beta decay in 76-Ge and low-energy solar neutrinos is discussed
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