4,679 research outputs found
Non-resonant kaon pair production and medium effects in proton-nucleus collisions
We study the non-resonant (non-) production of pairs by
protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets within the
collision model, based on the nuclear spectral function, for incoherent primary
proton--nucleon and secondary pion--nucleon creation processes. The model takes
into account the initial proton and final kaon absorption, target nucleon
binding and Fermi motion as well as nuclear mean-field potential effects on
these processes. We calculate the antikaon momentum dependences of the
exclusive absolute and relative pair yields in the acceptance window
of the ANKE magnetic spectrometer, used in a recent experiment performed at
COSY, within the different scenarios for the antikaon-nucleus optical
potential. We demonstrate that the above observables are strongly sensitive to
this potential. Therefore, they can be useful to help determine the
optical potential from the direct comparison of the results of our calculations
with the data from the respective ANKE-at-COSY experiment. We also show that
the pion--nucleon production channels dominate in the low-momentum ,
production in the considered kinematics and, hence, they have to be accounted
for in the analysis of these data.Comment: 19 page
Medium effects in pair production by 2.83 GeV protons on nuclei
We study pair production in the interaction of protons of 2.83
GeV kinetic energy with C, Cu, Ag, and Au target nuclei in the framework of the
nuclear spectral function approach for incoherent primary proton--nucleon and
secondary pion--nucleon production processes, and processes associated with the
creation of intermediate pairs. The approach accounts for the
initial proton and final hyperon absorption, final meson
distortion in nuclei, target nucleon binding, and Fermi motion, as well as
nuclear mean-field potential effects on these processes. We calculate the
momentum dependence of the absolute yield from the
target nuclei considered, in the kinematical conditions of the ANKE experiment,
performed at COSY, within the different scenarios for the -nucleus
effective scalar potential. We show that the above observable is appreciably
sensitive to this potential in the low-momentum region. Therefore, direct
comparison of the results of our calculations with the data from the
ANKE-at-COSY experiment can help to determine the above potential at finite
momenta. We also demonstrate that the two-step pion--nucleon production
channels dominate in the low-momentum production in the chosen
kinematics and, therefore, they have to be taken into account in the analysis
of these data.Comment: 29 page
Comment on ``Spin and cyclotron energies of electrons in GaAs/GaAlAs quantum wells''
In a recent publication, Pfeffer and Zawadzki [cond-mat/0607150; Phys. Rev. B
74, 115309 (2006)] attempted a calculation of electron g factor in III-V
heterostructures. The authors emphasize that their outcome is in strong
discrepancy with our original result [Ivchenko and Kiselev, Sov. Phys.
Semicond. 26, 827 (1992)] and readily conclude that ``the previous theory of
the g factor in heterostructures is inadequate''. We show here that the entire
discrepancy can be tracked down to an additional contribution missing in the
incomplete elimination procedure of Pfeffer and Zawadzki. This mistake equally
affects their ``exact'' and approximate results. When the overlooked terms
stemming from the nondiagonal Zeeman interaction between light hole and
spin-orbit-split valence states are taken into account in the effective
electron dispersion, the results of the both approaches applied to the
three-level kp model become identical.Comment: 5 pages, no figure
Direct photon production from hadronic sources in high-energy heavy-ion collisions
The low direct photon production from a variety of the hadronic sources
is studied within the microscopic HSD transport approach for p+C, p+Pb and
Pb+Pb collisions at 160 A GeV. The direct photon emission from elementary
hadronic scatterings as well as meson-meson bremsstrahlung are incorporated.
The influence of in-medium effects such as a collisional broadening of the
vector-meson spectral functions on the photon emission rate is found to be
hardly observable in the final spectra which are dominated by bremsstrahlung
type processes. The uncertainties in the subtraction of the 'background' from
the photon decay of hadronic resonances inside the hot and dense fireball is
investigated, additionally. Our findings are relevant for the interpretation
and extraction of experimental data on direct photon production at low .Comment: 25 pages, 10 figures, to be published in Phys. Rev.
Polarized Electric Current in Semiclassical Transport with Spin-Orbit Interaction
Semiclassical solutions of two-dimensional Schrodinger equation with
spin-orbit interaction and smooth potential are considered. In the leading
order, spin polarization is in-plane and follows the evolution of the electron
momentum for a given subband. Out-of-plane spin polarization appears as a
quantum correction, for which an explicit expression is obtained. We
demonstrate how spin-polarized currents can be achieved with the help of a
barrier or quantum point contact open for transmission only in the lower
subband.Comment: 6 pages, 2 figure
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