28,248 research outputs found
Nearby Doorways, Parity Doublets and Parity Mixing in Compound Nuclear States
We discuss the implications of a doorway state model for parity mixing in
compound nuclear states. We argue that in order to explain the tendency of
parity violating asymmetries measured in Th to have a common sign,
doorways that contribute to parity mixing must be found in the same energy
neighbourhood of the measured resonance. The mechanism of parity mixing in this
case of nearby doorways is closely related to the intermediate structure
observed in nuclear reactions in which compound states are excited. We note
that in the region of interest (Th) nuclei exhibit octupole
deformations which leads to the existence of nearby parity doublets. These
parity doublets are then used as doorways in a model for parity mixing. The
contribution of such mechanism is estimated in a simple model.Comment: 11 pages, REVTE
Learning by doing: Action performance facilitates affordance perception
AbstractWe investigated the effect of action performance on perceptual judgments by evaluating accuracy in judging whether doorways allowed passage. Participants made judgments either before or after walking through doorways of varying widths. Participants in the action-first group benefited from action feedback and made more accurate judgments compared to a perception-first group that judged doorways before walking through them. Action feedback aided perceptual judgments by facilitating scaling to body dimensions: Judgments in the action-first group were strongly related to height, weight, and torso size, whereas judgments in the perception-first group were not
Coherent and stochastic contributions of compound resonances in atomic processes: Electron recombination, photoionization and scattering
In open-shell atoms and ions, processes such as photoionization, combination
(Raman) scattering, electron scattering and recombination, are often mediated
by many-electron compound resonances. We show that their interference
(neglected in the independent-resonance approximation) leads to a coherent
contribution, which determines the energy-averaged total cross sections of
electron- and photon-induced reactions obtained using the optical theorem. In
contrast, the partial cross sections (e.g., electron recombination, or photon
Raman scattering) are dominated by the stochastic contributions. Thus, the
optical theorem provides a link between the stochastic and coherent
contributions of the compound resonances. Similar conclusions are valid for
reactions via compound states in molecules and nuclei
Theory of parity violation in compound nuclear states; one particle aspects
In this work we formulate the reaction theory of parity violation in compound
nuclear states using Feshbach's projection operator formalism. We derive in
this framework a complete set of terms that contribute to the longitudinal
asymmetry measured in experiments with polarized epithermal neutrons. We also
discuss the parity violating spreading width resulting from this formalism. We
then use the above formalism to derive expressions which hold in the case when
the doorway state approximation is introduced. In applying the theory we limit
ourselves in this work to the case when the parity violating potential and the
strong interaction are one-body. In this approximation, using as the doorway
the giant spin-dipole resonance and employing well known optical potentials and
a time-reversal even, parity odd one-body interaction we calculate or estimate
the terms we derived. In our calculations we explicitly orthogonalize the
continuum and bound wave functions. We find the effects of orthogonalization to
be very important. Our conclusion is that the present one-body theory cannot
explain the average longitudinal asymmetry found in the recent polarized
neutron experiments. We also confirm the discrepancy, first pointed out by
Auerbach and Bowman, that emerges, between the calculated average asymmetry and
the parity violating spreading width, when distant doorways are used in the
theory.Comment: 37 pages, REVTEX, 5 figures not included (Postscript, available from
the authors
Fine Structure Discussion of Parity-Nonconserving Neutron Scattering at Epithermal Energies
The large magnitude and the sign correlation effect in the parity
non-conserving resonant scattering of epithermal neutrons from Th is
discussed in terms of a non-collective local doorway model. General
conclusions are drawn as to the probability of finding large parity violation
effects in other regions of the periodic table.Comment: 6 pages, Tex. CTP# 2296, to appear in Z. Phys.
Production of doubly strange hypernuclei via {\Xi}- doorways in the 16O(K-, K+) reaction at 1.8 GeV/c
We examine theoretically production of doubly strange hypernuclei, 16 {\Xi}-C
and 16 {\Lambda}{\Lambda}C, in doublecharge exchange 16O(K-, K+) reactions
using a distorted-wave impulse approximation. The inclusive K+ spectrum at the
incident momentum pK- = 1.8 GeV/c and scattering angle {\theta}lab = 0^{\circ}
is estimated in a one-step mechanism, K-p \to K+{\Xi}- via {\Xi}- doorways
caused by a {\Xi}-p-{\Lambda}{\Lambda} coupling. The calculated spectrum in the
{\Xi}- bound region indicates that the integrated cross sections are on the
order of 7-12 nb/sr for significant 1- excited states with 14C(0+, 2+) \otimes
s{\Lambda}p{\Lambda} configurations in 16 {\Lambda}{\Lambda}C via the doorway
states of the spin-stretched 15N(1/2-, 3/2-) \otimes s{\Xi}- in 16 {\Xi}-C due
to a high momentum transfer q{\Xi}- \approx 400 MeV/c. The {\Xi}- admixture
probabilities of these states are on the order of 5-9%. However, populations of
the 0+ ground state with 14C(0+) \otimes s2{\Lambda} and the 2+ excited state
with 14C(2+) \otimes s2 {\Lambda} are very small. The sensitivity of the
spectrum on the {\Xi}N-{\Lambda}{\Lambda} coupling strength enables us to
extract the nature of {\Xi}N-{\Lambda}{\Lambda} dynamics in nuclei, and the
nuclear (K-, K+) reaction can extend our knowledge of the S = -2 world.Comment: 10 pages, 3 figure
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