118 research outputs found
Possible doublet mechanism for a regular component of parity violation in neutron scattering
A nucleus with octupole deformation of the mean field reveals rotational
doublets with the same angular momentum and opposite parity. Mediated by the
Coriolis-type interaction, the doublet structure leads to a strong regular
component in the parity violation caused by weak interaction. This can explain
sign correlations observed in polarized neutron scattering by Th.Comment: 10 pages, revtex, no figure
4He experiments can serve as a database for determining the three-nucleon force
We report on microscopic calculations for the 4He compound system in the
framework of the resonating group model employing realistic nucleon-nucleon and
three nucleon forces. The resulting scattering phase shifts are compared to
those of a comprehensive R-matrix analysis of all data in this system, which
are available in numerical form. The agreement between calculation and analysis
is in most cases very good. Adding three-nucleon forces yields in many cases
large effects. For a few cases the new agreement is striking. We relate some
differencies between calculation and analysis to specific data and discuss
neccessary experiments to clarify the situation. From the results we conclude
that the data of the 4He system might be well suited to determine the structure
of the three-nucleon force.Comment: title changed,note added, format of figures changed, appearance of
figures in black-and-white changed, Phys. Rev. C accepte
P- and T-violation Tests with Polarized Resonance Neutrons
The enhancements of CP-violating effects in resonance neutron
transmissionthrough polarized targets are studied for 2 possible versions of
experiment. The importance is stressed of error analysis and of pseudomagnetic
effects' compensation.Comment: 11 pages, LaTeX + 4 PostScript figure
Microscopic calculation of the spin-dependent neutron scattering lengths on 3He
We report on the spin.dependent neutron scattering length on 3He from a
microscopic calculation of p-3H, n-3He, and d-2H scattering employing the
Argonne v18 nucleon-nucleon potential with and without additional three-nucleon
force. The results and that of a comprehensive R-matrix analysis are compared
to a recent measurement. The overall agreement for the scattering lengths is
quite good. The imaginary parts of the scattering lengths are very sensitive to
the inclusion of three-nucleon forces, whereas the real parts are almost
insensitive.Comment: 9 pages, 1 figur
UCN anomalous losses and the UCN capture cross-section on material defects
Experimental data shows anomalously large Ultra Cold Neutrons (UCN)
reflection losses and that the process of UCN reflection is not completely
coherent. UCN anomalous losses under reflection cannot be explained in the
context of neutron optics calculations. UCN losses by means of incoherent
scattering on material defects are considered and cross-section values
calculated. The UCN capture cross-section on material defects is enhanced by a
factor of 10^4 due to localization of UCN around defects. This phenomenon can
explain anomalous losses of UCN.Comment: 13 pages, 4 figure
Limits of Time-Reversal Violating Interaction from Compound Nuclear Experiments
Mean square matrix elements of the time reversal invariance violating (TRIV)
interaction between the compound nuclear states are calculated within the
statistical model, using the explicit form of the TRIV interaction via the
-meson exchange. From the comparison of the calculated values with the
data known for reaction, and for
-correlation measurements in process, the
bounds on the TRIV constant are obtained {\bar g}_{\rho} \alt 1.8 \times
10^{-2} and {\bar g}_{\rho} \alt 1.1 \times 10^{-2}. The sensitivity of the
recently proposed detailed balance test experiments on isolated resonances in
to the value of is shown to be as high as to reach
values .Comment: Phys. Lett. B; to be published, 16 pages, REVTEX 3, no figure
Optical-Model Description of Time-Reversal Violation
A time-reversal-violating spin-correlation coefficient in the total cross
section for polarized neutrons incident on a tensor rank-2 polarized target is
calculated by assuming a time-reversal-noninvariant, parity-conserving
``five-fold" interaction in the neutron-nucleus optical potential. Results are
presented for the system for neutron incident energies
covering the range 1--20 MeV. From existing experimental bounds, a strength of
keV is deduced for the real and imaginary parts of the five-fold
term, which implies an upper bound of order on the relative -odd
strength when compared to the central real optical potential.Comment: 11 pages (Revtex
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
Study of levitating nanoparticles using ultracold neutrons
Physical adsorption of atoms, molecules and clusters on surface is known. It
is linked to many phenomena in physics, chemistry, and biology. Usually the
studies of adsorption are limited to the particle sizes of up to ~10^2-10^3
atoms. Following a general formalism, we apply it to even larger objects and
discover qualitatively new phenomena. A large particle is bound to surface in a
deep and broad potential well formed by van der Waals/ Casimir-Polder forces.
The well depth is significantly larger than the characteristic thermal energy.
Nanoparticles in high-excited bound states form two-dimensional gas of objects
quasi-freely traveling along surface. A particularly interesting prediction is
small-energy-transfer scattering of UCN on solid/ liquid surfaces covered by
such levitating nanoparticles/ nano-droplets. The change in UCN energy is due
to the Doppler shift induced by UCN collisions with nanoparticles; the energy
change is about as small as the UCN initial energy. We compare theoretical
estimations of our model to all relevant existing data and state that they
agree quite well. As our theoretical formalism provides robust predictions and
the experimental data are rather precise, we conclude that the recently
discovered intriguing phenomenon of small heating of UCN in traps is due to
their collisions with such levitating nanoparticles. Moreover, this new
phenomenon might be relevant to the striking contradiction between results of
the neutron lifetime measurements with smallest reported uncertainties as it
might cause major false effects in these experiments; thus it affects
fundamental conclusions concerning precision checks of unitarity of the
Cabibbo-Kobayashi-Maskawa matrix, cosmology, astrophysics. Dedicated
measurements of UCN up-scattering on specially prepared surfaces and
nanoparticles levitating above them might provide a unique method to study
surface potentials.Comment: 20 pages, 12 figure
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