358 research outputs found
Photodisintegration of the deuteron in the few GeV region using asymptotic amplitudes
Exclusive photodisintegration of the deuteron in the 1-4GeV range is
described in terms of a simple covariant and gauge invariant approach using an
effective counting rule as the hard part of the d-np vertex.
At a scattering angle of theta_cm=90 degrees a prescaling behavior of the
differential cross section proportional to 1/s^(n-2) with n ~ 12 is obtained;
going away from 90 degrees the value of n decreases slowly, in qualitative
agreement with the recent data.Comment: 10 pages, 3 figures, to appear in Physics Letters
Preserving the gauge invariance of meson production currents in the presence of explicit final-state interactions
A comprehensive formalism is developed to preserve the gauge invariance of
currents describing the photo- or electroproduction of mesons off the nucleon
when the final-state interactions of mesons and nucleons is taken into account
explicitly. Replacing exchange currents by auxiliary currents, it is found that
all contributions due to explicit final-state interactions are purely
transverse and do not contain a Kroll-Ruderman-type contact current. The
relation of the present formulation to tree-level-type prescriptions is shown.Comment: 6 pages, 2 figures; published versio
An innovative technique for the investigation of the 4-fold forbidden beta-decay of V
For the first time a Vanadium-based crystal was operated as cryogenic
particle detector. The scintillating low temperature calorimetric technique was
used for the characterization of a 22 g YVO crystal aiming at the
investigation of the 4-fold forbidden non-unique decay of V.
The excellent bolometric performance of the compound together with high light
output of the crystal makes it an outstanding technique for the study of such
elusive rate process. The internal radioactive contaminations of the crystal
are also investigated showing that an improvement on the current status of
material selection and purification are needed, U and Th
are measured at the level of 28 mBq/kg, 1.3 Bq/kg and 28 mBq/kg, respectively.
In this work, we also discuss a future upgrade of the experimental set-up which
may pave the road for the detection of the rare V decay
First limits on double beta decays in Th
As one of the primordial radioactive isotopes, Th mainly undergoes
-decay with a half-life of yr. However, it is
also one of 35 double beta decay candidates in which the single -decay
is forbidden or strongly suppressed. 181 mg of thorium contained in a gas
mantle was measured in an HPGe well-detector at the Gran Sasso Underground
Laboratory (LNGS) with a total exposure of 3.25 g d. We obtain
half-life limits on all double beta decay modes of Th to excited states
of U on the order of yr. For the most likely transition
into the state we find a lower half-life limit of
yr (90% credibility). These are the first constraints on double beta decay
excited state transition in Th
A new investigation of half-lives for the decay modes of V
A new search for the decay modes of the 4-fold forbidden non-unique decay of
V has been performed at the Gran Sasso Underground Laboratory (LNGS). In
total an exposure of 197 kg d has been accumulated. The half-life for
the electron capture into the first excited state of Ti has been
measured with the highest precision to date as yr (68% C.I.) in which systematics uncertainties dominate. The search
for the -decay into the first excited state of Cr resulted in a
lower limit of yr (90% C.I.), which is an improvement of
almost one order of magnitude compared to existing results. The sensitivity of
the new measurement is now in the region of theoretical predictions
Electromagnetic properties of off-shell particles and gauge invariance
Abstract: Electromagnetic properties of off-shell particles are discussed on the basis of a purely electromagnetic reaction: virtual Compton scattering off a proton. It is shown that the definition of off-shell electromagnetic form factors is not gauge invariant and that these cannot be investigated in practice. Using only fundamental requirements of gauge invariance it is demonstrated that off-shell effects are cancelled in the longitudinal components of the total conserved current by the minimal contact current, while the off-shellness appears only in the the transverse (gauge invariant) non-pole part. This provides the possibility to introduce an on-shell extrapolated form factor F_1^+(q^2) in a gauge invariant way for the unphysical time-like region, 4m_e^
On the possibility to search for double beta decay of initially unstable (alpha/beta radioactive) nuclei
Possibilities to search for double beta decay of alpha/beta unstable nuclei,
many of which have higher energy release than "conventional" (beta stable)
double beta decay candidates, are discussed. First experimental half-life
limits on double beta decay of radioactive nuclides from U and Th families
(trace contaminants of the CaWO_4, CdWO_4 and Gd_2SiO_5 scintillators) were
established by reanalyzing the data of low-background measurements in the
Solotvina Underground Laboratory with these detectors (1734 h with CaWO_4,
13316 h with CdWO_4, and 13949 h with Gd_2SiO_5 crystals).Comment: 15 pages, 6 figure
Experimental Performance Evaluation of a High Speed Permanent Magnet Synchronous Motor and Drive for a Flywheel Application at Different Frequencies
This paper presents the results of an experimental performance characterization study of a high speed, permanent magnet motor/generator (M/G) and drive applied to a flywheel module. Unlike the conventional electric machine the flywheel M/G is not a separated unit; its stator and rotor are integrated into a flywheel assembly. The M/G rotor is mounted on a flywheel rotor, which is magnetically levitated and sealed within a vacuum chamber during the operation. Thus, it is not possible to test the M/G using direct load measurements with a dynamometer and torque transducer. Accordingly, a new in-situ testing method had to be developed. The paper describes a new flywheel M/G and drive performance evaluation technique, which allows the estimation of the losses, efficiency and power quality of the flywheel high speed permanent magnet M/G, while working in vacuum, over wide frequency and torque ranges. This method does not require any hardware modification nor any special addition to the test rig. This new measurement technique is useful for high-speed applications, when applying an external load is technically difficult
Updated and novel limits on double beta decay and dark matter-induced processes in platinum
A 510 day long-term measurement of a 45.3 g platinum foil acting as the
sample and high voltage contact in an ultra-low-background high purity
germanium detector was performed at Laboratori Nazionali del Gran Sasso
(Italy). The data was used for a detailed study of double beta decay modes in
natural platinum isotopes. Limits are produced in the range
a for double beta decay to excited states (90%
C.L.) confirming, and partially extending existing limits. The highest
sensitivity, greater than a, was achieved for the and resonant
modes of double electron capture involving KL shell electrons.
Additionally, novel limits for inelastic dark matter scattering on Pt
are placed up to mass splittings of approximately 500 keV. We analyze several
techniques to extend the sensitivity and propose a few approaches for future
medium-scale experiments with platinum-group elements.Comment: 15 pages, 3 figure
Background suppression in massive TeO bolometers with Neganov-Luke amplified light detectors
Bolometric detectors are excellent devices for the investigation of
neutrinoless double-beta decay (0). The observation of such
decay would demonstrate the violation of lepton number, and at the same time it
would necessarily imply that neutrinos have a Majorana character. The
sensitivity of cryogenic detectors based on TeO is strongly limited by the
alpha background in the region of interest for the 0 of
Te. It has been demonstrated that particle discrimination in TeO
bolometers is possible measuring the Cherenkov light produced by particle
interactions. However an event-by-event discrimination with NTD-based light
detectors has to be demonstrated. We will discuss the performance of a
highly-sensitive light detector exploiting the Neganov-Luke effect for signal
amplification. The detector, being operated with NTD-thermistor and coupled to
a 750 g TeO crystal, shows the ability for an event-by-event identification
of electron/gamma and alpha particles. The extremely low detector baseline
noise, RMS 19 eV, demonstrates the possibility to enhance the sensitivity of
TeO-based 0 experiment to an unprecedented level
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