22,491 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
On Which Length Scales Can Temperature Exist in Quantum Systems?
We consider a regular chain of elementary quantum systems with nearest
neighbor interactions and assume that the total system is in a canonical state
with temperature . We analyze under what condition the state factors into a
product of canonical density matrices with respect to groups of subsystems
each, and when these groups have the same temperature . While in classical
mechanics the validity of this procedure only depends on the size of the groups
, in quantum mechanics the minimum group size also depends
on the temperature ! As examples, we apply our analysis to different types
of Heisenberg spin chains.Comment: To appear in: Proceedings of the SPQS conference, J. Phys. Soc. Jpn.
74 (2005) Supp
VO2: a two-fluid incoherent metal?
We present {\it ab initio} LDA+DMFT results for the many-particle density of
states of on the metallic side of the strongly first-order
(-driven) insulator-metal transition. In strong contrast to LDA predictions,
there is {\it no} remnant of even correlated Fermi liquid behavior in the
correlated metal. Excellent quantitative agreement with published photoemission
and X-ray absorption experiments is found in the metallic phase. We argue that
the absence of FL-quasiparticles provides a natural explanation for the
bad-metallic transport for . Based on this agreement, we propose
that the I-M transition in is an orbital-selective Mott transition,
and point out the relevance of orbital resolved one-electron and optical
spectroscopy to resolve this outstanding issue.Comment: 4 pages, 3 figure
Few-Particle Effects in Semiconductor Quantum Dots: Observation of Multi-Charged-Excitons
We investigate experimentally and theoretically few-particle effects in the
optical spectra of single quantum dots (QDs). Photo-depletion of the QD
together with the slow hopping transport of impurity-bound electrons back to
the QD are employed to efficiently control the number of electrons present in
the QD. By investigating structurally identical QDs, we show that the spectral
evolutions observed can be attributed to intrinsic, multi-particle-related
effects, as opposed to extrinsic QD-impurity environment-related interactions.
From our theoretical calculations we identify the distinct transitions
related to excitons and excitons charged with up to five additional electrons,
as well as neutral and charged biexcitons.Comment: 4 pages, 4 figures, revtex. Accepted for publication in Physical
Review Letter
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