1,734 research outputs found
On the muon neutrino mass
During the runs of the PS 179 experiment at LEAR of CERN, we photographed an
event of antiproton-Ne absorption, with a complete pi+ -> mu+ ->e+ chain. From
the vertex of the reaction a very slow energy pi+ was emitted. The pi+ decays
into a mu+ and subsequently the mu+ decays into a positron. At the first decay
vertex a muon neutrino was emitted and at the second decay vertex an electron
neutrino and a muon antineutrino. Measuring the pion and muon tracks and
applying the momentum and energy conservation and using a classical statistical
interval estimator, we obtained an experimental upper limit for the muon
neutrino mass: m_nu < 2.2 MeV at a 90% confidence level. A statistical analysis
has been performed of the factors contributing to the square value of the
neutrino mass limit.Comment: 18 pages, 5 eps figure
Constraining Antimatter Domains in the Early Universe with Big Bang Nucleosynthesis
We consider the effect of a small-scale matter-antimatter domain structure on
big bang nucleosynthesis and place upper limits on the amount of antimatter in
the early universe. For small domains, which annihilate before nucleosynthesis,
this limit comes from underproduction of He-4. For larger domains, the limit
comes from He-3 overproduction. Most of the He-3 from antiproton-helium
annihilation is annihilated also. The main source of He-3 is
photodisintegration of He-4 by the electromagnetic cascades initiated by the
annihilation.Comment: 4 pages, 2 figures, revtex, (slightly shortened
High efficiency thermionic converter studies
The objective is to improve thermionic converter performance by means of reduced interelectrode losses, greater emitter capabilities, and lower collector work functions until the converter performance level is suitable for out-of-core space reactors and radioisotope generators. Electrode screening experiments have identified several promising collector materials. Back emission work function measurements of a ZnO collector in a thermionic diode have given values less than 1.3 eV. Diode tests were conducted over the range of temperatures of interest for space power applications. Enhanced mode converter experiments have included triodes operated in both the surface ionization and plasmatron modes. Pulsed triodes were studied as a function of pulse length, pulse potential, inert gas fill pressure, cesium pressure, spacing, emitter temperature and collector temperature. Current amplifications (i.e., mean output current/mean grid current) of several hundred were observed up to output current densities of one amp/sq cm. These data correspond to an equivalent arc drop less than 0.1 eV
High efficiency thermionic converter studies
Research in thermionic energy conversion technology is reported. The objectives were to produce converters suitable for use in out of core space reactors, radioisotope generators, and solar satellites. The development of emitter electrodes that operate at low cesium pressure, stable low work function collector electrodes, and more efficient means of space charge neutralization were investigated to improve thermionic converter performance. Potential improvements in collector properties were noted with evaporated thin film barium oxide coatings. Experiments with cesium carbonate suggest this substance may provide optimum combinations of cesium and oxygen for thermionic conversion
Apparent high metallicity in 3-4 keV galaxy clusters: the inverse iron-bias in action in the case of the merging cluster Abell 2028
Recent work based on a global measurement of the ICM properties find evidence
for an increase of the iron abundance in galaxy clusters with temperature
around 2-4 keV up to a value about 3 times larger than that typical of very hot
clusters. We have started a study of the metal distribution in these objects
from the sample of Baumgartner et al. (2005), aiming at resolving spatially the
metal content of the ICM. We report here on a 42ks XMM observation of the first
object of the sample, the cluster Abell 2028. The XMM observation reveals a
complex structure of the cluster over scale of 300 kpc, showing an interaction
between two sub-clusters in cometary-like configurations. At the leading edges
of the two substructures cold fronts have been detected. The core of the main
subcluster is likely hosting a cool corona. We show that a one-component fit
for this region returns a biased high metallicity. This inverse iron bias is
due to the behavior of the fitting code in shaping the Fe-L complex. In
presence of a multi-temperature structure of the ICM, the best-fit metallicity
is artificially higher when the projected spectrum is modeled with a single
temperature component and it is not related to the presence of both Fe-L and
Fe-K emission lines in the spectrum. After accounting for the bias, the overall
abundance of the cluster is consistent with the one typical of hotter, more
massive clusters. We caution the interpretation of high abundances inferred
when fitting a single thermal component to spectra derived from relatively
large apertures in 3-4 keV clusters, because the inverse iron bias can be
present. Most of the inferences trying to relate high abundances in 3-4 keV
clusters to fundamental physical processes will likely have to be revised.Comment: 13 pages, 8 figures.Accepted for publication in Astronomy and
Astrophysycs. Minor changes to match published versio
Solving the cosmic lithium problems with primordial late-decaying particles
We investigate the modifications to predictions for the abundances of light
elements from standard Big-Bang nucleosynthesis when exotic late-decaying
particles with lifetimes exceeding ~1 sec are prominent in the early Universe.
Utilising a model-independent analysis of the properties of these long-lived
particles, we identify the parameter space associated with models that are
consistent with all observational data and hence resolve the much discussed
discrepancies between observations and theoretical predictions for the
abundances of Li^7 and Li^6.Comment: 6 pages, 3 figures, submitted to Physical Review D; minor changes to
reference
XMM-Newton spectral properties of the Ultraluminous IRAS Galaxy Mrk 273
We present a 23 ks XMM-Newton observation of the ULIRG Mrk 273. The hard
X-ray spectrum can be modeled by a highly absorbed power law plus an Fe Kalpha
emission line. The iron line is broad, suggesting possible superposition of a
neutral iron line at 6.4 keV, and a blend of ionized iron lines from Fe XXV and
Fe XXVI. Given the relatively short exposure, the three line components can not
be singularly resolved with high statistical significance: the neutral
component is detected at ~2.5sigma and the Fe XXV line at ~2sigma c.l., while
for the Fe XXVI line we can only estimate an upper limit. The broad band
spectrum requires, in addition to a highly absorbed power law, at least three
collisionally ionized plasma components, which may be associated with
star-forming regions. The temperatures of the three plasmas are about 0.3, 0.8
and 6 keV, where the highest of the three is sufficient to produce ionized iron
emission lines. An alternative interpretation for the origin of the soft
emission might also be given in terms of reflection off some photoionized gas,
as has been observed in a number of nearby Compton-thick Seyfert 2 galaxies. A
hot gas, photoionized by the primary, continuum can also produce ionized iron
lines. Unfortunately, given the limited statistics and the lack of high
resolution spectroscopy, it is not possible to distinguish between the two
models investigated. We further compare the XMM-Newton findings with the
Chandra data obtaining consistent spectral results. The absorption corrected
hard X-ray (2-10 keV) luminosity of Mrk 273 corresponds to ~0.2% of the far-IR
luminosity, similar to typical values found in pure starbursts. The thermal
contribution to the soft X-ray luminosity is ~0.2-0.7x10^42 erg s^-1,
comparable to those found in NGC 6240 and other starburst dominated ULIRGs.Comment: 10 pages, 10 figures, 4 tables, accepted for publication in Astronomy
and Astrophysi
Production of Mesons in the Reaction at 3.67 GeV/c
The ratio of the total exclusive production cross sections for
and mesons has been measured in the reaction at
GeV/c. The observed ratio is
from which the exclusive
meson production cross section is determined to be
. Differential cross section
distributions have been measured. Their shape is consistent with isotropic
meson production.Comment: 14 pages, 5 figures, accepted by Phys.Lett.
Two-body Photodisintegration of He with Full Final State Interaction
The cross sections of the processes He()H and
He()He are calculated taking into account the full final
state interaction via the Lorentz integral transform (LIT) method. This is the
first consistent microscopic calculation beyond the three--body breakup
threshold. The results are obtained with a semirealistic central NN potential
including also the Coulomb force. The cross sections show a pronounced dipole
peak at 27 MeV which lies within the rather broad experimental band. At higher
energies, where experimental uncertainties are considerably smaller, one finds
a good agreement between theory and experiment. The calculated sum of three--
and four--body photodisintegration cross sections is also listed and is in fair
agreement with the data.Comment: 18 pages, 6 figure
Fragmentation studies of high energy ions using CR39 nuclear track detectors
We report on the measurements of the total charge changing fragmentation
cross sections in high-energy nucleus-nucleus collisions using Fe, Si and Pb
incident ions. Several stacks of CR39 nuclear track detectors with different
target combinations were exposed at normal incidence to high energy accelerator
beams to integrated densities of about 2000 ions/cm^2. The nuclear track
detector foils were chemically etched, and ion tracks were measured using an
automatic image analyzer system. The cross section determination is based on
the charge identification of beam ions and their fragments and on the
reconstruction of their path through the stacks.Comment: 5 pages, 4 EPS figures. Corrected Eq. 3 and Table 1. Presented at the
10th Inter. Symp. Radiat. Phys., Coimbra, Portugal, 17-22 Sept. 200
- …