613 research outputs found
K production in proton-nucleus reactions and the role of momentum-dependent potentials
The production of mesons in proton-nucleus collisions from 1.0 to 2.5
GeV is analyzed with respect to one-step nucleon-nucleon ) and
two-step -nucleon ) or pion-nucleon ) production channels on the basis of a coupled-channel transport
approach (CBUU) including the kaon final state interactions. The influence of
momentum-dependent potentials for the nucleon, hyperon and kaon in the final
state are studied as well as the importance of elastic rescattering in
the target nucleus. The transport calculations are compared to the experimental
spectra taken at LBL Berkeley, SATURNE, CELSIUS, GSI and COSY-J\"ulich.
It is found that the momentum-dependent baryon potentials effect the excitation
function of the cross section; at low bombarding energies of 1.0
GeV the attractive baryon potentials in the final state lead to a relative
enhancement of the kaon yield whereas the net repulsive potential at bombarding
energies 2 GeV causes a decrease of the cross section. Furthermore
it is pointed out, that especially the spectra at low momenta (or kinetic
energy ) allow to determine the in-medium potential almost model
independently due to a relative shift of the spectra in kinetic energy
that arises from the acceleration of the kaons when propagating out of the
nuclear medium to free space, i.e. converting potential energy to kinetic
energy of the free kaon.Comment: 11 pages, LaTeX, including 10 postscript figures, submitted to Eur.
Phys. J.
Transport analysis of K+ production in proton-nucleus reactions
The production of mesons in proton-nucleus collisions from 1.0 to 2.3
GeV is analyzed with respect to one-step nucleon-nucleon ) and
two-step -nucleon ) or pion-nucleon ) production channels on the basis of a coupled-channel transport
approach (CBUU) including the kaon final-state-interactions (FSI).
Momentum-dependent potentials for the nucleon, hyperon and kaon in the final
state are included as well as elastic rescattering in the target nucleus.
The transport calculations are compared to the experimental spectra taken
at COSY-J\"ulich. Our systematic analysis of spectra from ,
, and targets as well as their momentum
differential ratios gives a repulsive potential of MeV at
normal nuclear matter density.Comment: 7 pages, 5 figures, submitted to Eur. Phys. J.
Nonmesonic decay of the Lambda-hyperon in hypernuclei produced by p+Au collisions
The lifetime of the Lambda-hyperon for the nonmesonic decay Lambda N ---> N N
has been determined by a measurement at COSY Juelich of the delayed fission of
heavy hypernuclei produced in proton - Au collisions at T_p=1.9 GeV. It is
found that heavy hypernuclei with mass numbers A= 180 +- 5 and atomic numbers
Z= 74 +-2 fission with a lifetime
130ps +- 13ps (stat.) +- 15ps (syst.) . This value together with the results
obtained for other heavy hypernuclei in previous investigations indicates (on
the confidence level of 0.9) a violation of the phenomenological Delta I = 1/2
rule for Lambda N ---> NN transitions as known from the weak mesonic decays of
kaons and hyperons. PACS:
{13.30.-a}{Decays of baryons}
{13.75.Ev}{Hyperon-nucleon interaction}
{21.80}{Hypernuclei}
{25.80.Pw}{Hyperon-induced reactions}Comment: 3 pages, 2 Postscript figures, uses svepj.clo and svjour.cls.
submitted to European Physical Journal
On the Delta I = 1/2 rule in the Lambda N ----> N N reaction
It is shown that the mass dependence of the -lifetime in heavy
hypernuclei is sensitive to the ratio of neutron-induced to proton-induced
non-mesonic decay rates R_n/R_p. A comparison of the experimental mass
dependence of the lifetimes with the calculated ones for different values of
R_n/R_p leads to the conclusion that this ratio is larger than 2 on the
confidence level of 0.75. This suggests that the phenomenological I=1/2
rule might be violated for the nonmesonic decay of the -hyperon.Comment: 3 pages, 2 figures, to be published in European Physical Journal
The lifetime of the Lambda hyperon bound in hypernuclei produced by p+U collisions
The nonmesonic decay of the Lambda hyperon has been investigated by
observation of delayed fission from heavy hypernuclei produced in proton-U
collisions at Tp = 1.9 GeV. The lifetime of heavy hypernuclei with masses A
approximately 220 obtained in the present work, i.e.
tau = 138 +- 6 (stat.) +-m 17 (syst.) ps,
is the most accurate result for heavy hypernuclei produced in proton and
antiproton induced collisions on a U target so far.
PACS: {13.30.-a}{Decays of baryons} {13.75.Ev}{Hyperon-nucleon interaction}
{21.80}{Hypernuclei} {25.80.Pw}{Hyperon-induced reactions}Comment: 16 pages, 4 Postscript figures, uses file appolb.cls (included),
submitted to Acta Physica Polonica B, http://th-www.if.uj.edu.pl/act
Nonmesonic decay of the Lambda hyperon in nuclear matter - implications on the weak Lambda-N interaction
The lifetime of the Lambda hyperon in heavy hypernuclei as measured by the
COSY-13 Collaboration in proton - Au, Bi and U collisions has been analysed to
yield tau(Lambda) = (145 +- 11) ps. This value for tau(Lambda) is compatible
with the lifetime extracted from antiproton annihilation on Bi and U targets,
however, much more accurate. We find that the dependence of the lifetime
tau(Lambda) on the mass of hypernuclei indicates a violation of the
phenomenological Delta I = 1/2 rule known from the weak mesonic decays of
strange particles. PACS: {13.30.-a}{Decays of baryons}
{13.75.Ev}{Hyperon-nucleon interaction} {21.80}{Hypernuclei}
{25.80.Pw}{Hyperon-induced reactions}Comment: 21 pages, 11 PostScript figures, EPJA in prin
Basal crevasses in Larsen C Ice Shelf and implications for their global abundance
Basal crevasses extend upwards from the base of ice bodies and can penetrate more than halfway through the ice column under conditions found commonly on ice shelves. As a result, they may locally modify the exchange of mass and energy between ice shelf and ocean, and by altering the shelf's mechanical properties could play a fundamental role in ice shelf stability. Although early studies revealed that such features may be abundant on Antarctic ice shelves, their geometrical properties and spatial distribution has gained little attention. We investigate basal crevasses in Larsen C Ice Shelf using field radar survey, remote sensing and numerical modelling. We demonstrate that a group of features visible in MODIS imagery are the surface expressions of basal crevasses in the form of surface troughs, and find that basal crevasses can be generated as a result of stresses well downstream of the grounding line. We show that linear elastic fracture mechanics modelling is a good predictor of basal crevasse penetration height where stresses are predominantly tensile, and that measured surface trough depth does not always reflect this height, probably because of snow accumulation in the trough, marine ice accretion in the crevasse, or stress bridging from the surrounding ice. We conclude that all features visible in MODIS imagery of ice shelves and previously labelled simply as "crevasses", where they are not full thickness rifts, must be basal crevasse troughs, highlighting a fundamental structural property of many ice shelves that may have been previously overlooked
Bulk meltwater flow and liquid water content of snowpacks mapped using the electrical self-potential (SP) method
Our ability to measure, quantify and assimilate hydrological properties and processes of snow in operational models is disproportionally poor compared to the significance of seasonal snowmelt as a global water resource and major risk factor in flood and avalanche forecasting. We show here that strong electrical self-potential fields are generated in melting in situ snowpacks at Rhone Glacier and Jungfraujoch Glacier, Switzerland. In agreement with theory, the diurnal evolution of self-potential magnitudes ( ∼ 60–250mV) relates to those of bulk meltwater fluxes (0–1.2 × 10−6m3s−1) principally through the permeability and the content, electrical conductivity and pH of liquid water. Previous work revealed that when fresh snow melts, ions are eluted in sequence and electrical conductivity, pH and self-potential data change diagnostically. Our snowpacks had experienced earlier stages of melt, and complementary snow pit measurements revealed that electrical conductivity ( ∼ 1–5 × 10−6Sm−1) and pH ( ∼ 6.5–6.7) as well as permeabilities (respectively  ∼ 9.7 × 10−5 and  ∼ 4.3 × 10−5m2 at Rhone Glacier and Jungfraujoch Glacier) were invariant. This implies, first, that preferential elution of ions was complete and, second, that our self-potential measurements reflect daily changes in liquid water contents. These were calculated to increase within the pendular regime from  ∼ 1 to 5 and  ∼ 3 to 5.5% respectively at Rhone Glacier and Jungfraujoch Glacier, as confirmed by ground truth measurements. We conclude that the electrical self-potential method is a promising snow and firn hydrology sensor owing to its suitability for (1) sensing lateral and vertical liquid water flows directly and minimally invasively, (2) complementing established observational programs through multidimensional spatial mapping of meltwater fluxes or liquid water content and (3) monitoring autonomously at a low cost. Future work should focus on the development of self-potential sensor arrays compatible with existing weather and snow monitoring technology and observational programs, and the integration of self-potential data into analytical frameworks.ISSN:1994-0416ISSN:1994-042
The g-factor of the 21/2 state in Nb
The Y(, 2n)Nb reaction was used to populate excited states in Nb. The rotation of the angular distribution of the 357 keV gamma-transition from the 21/2 state was measured in an external magnetic field. The IPAD method was used. By applying =(1.33 0.14) ns for the lifetime of the 21/2 state at 3467 keV, the value of the g-factor 1.18 0.18 was derived
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