588 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.
Observations of stratospheric source gas profiles during the Arctic winter
An international campaign was performed at ESRANGE rocket base, near Kiruna, Sweden (68 N) from January 4 to February 15 in order to investigate the Chemistry of Ozone in the Polar Stratosphere (CHEOPS). Within the framework of this campaign two sets of large stratospheric air samples were collected by means of a balloon borne cryogenic air sampler. The two balloons were launched on February 1, and February 10, 1988. At present the samples are analyzed in our laboratory for their contents of several long lived trace gases such as CH4, N2O, H2, CO2, CO and the major halocarbons CH3Cl, CFCl3, CF2Cl2, CCl4, CH3CCl3, and C2F3Cl3. The vertical profiles derived from these samples will be presented and compared with previous observations made in February 1987. The data will be discussed in view of the dynamical evolution of the Arctic polar vortex during this winter
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.
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
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
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
Heat and groundwater transport between the Antarctic Ice Sheet and subglacial sedimentary basins from electromagnetic geophysical measurements
Numerical models of contemporary as well as paleo-ice sheets suggest that groundwater and heat exchanges between subglacial sedimentary basins and the ice sheet above, can be substantial and influence the flow of ice above. So far, an approach for the measurement and assessment of such heat fluxes has not been available. Here, we summarise existing evidence for groundwater and heat exchanges between contemporary and paleo ice sheets and the substrate below. We then explain the utility of electromagnetic geophysical measurements in elucidating such exchanges, and present magnetotelluric synthetic models of the deep sedimentary basin beneath the Institute Ice Stream in West Antarctica by way of illustration. Finally, we propose a simple empirical model by which heat exchanges between subglacial sedimentary basins and the overlying ice sheet can be estimated to first-order from electromagnetic data
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