496 research outputs found
Hyperfine Populations Prior to Muon Capture
It is shown that the 1S level hyperfine populations prior to muon capture
will be statistical when either target or beam are unpolarised independent of
the atomic level at which the hyperfine interaction becomes appreciable. This
assertion holds in the absence of magnetic transitions during the cascade and
is true because of minimal polarisation after atomic capture and selective
feeding during the cascade.Comment: (revtex, 6 preprint pages, no figures
The reaction cross section
The one- and two-step mechanisms of the reaction in
the range of incident proton kinetic energy 1.13-3.0 GeV have been
investigated. A remarkable peculiarity of the two-step mechanism which
incorporates subprocesses and is the so
called velocity matching providing the presence of all intermediate particles
nearly to the on-mass-shell. The differential cross section has been calculated
using a realistic model for the hypertritium wave function. The
maximum value of the cross section is estimated as 1nb/sr. The
contribution of the one-step mechanism with the elementary process into the cross section has been found to be two - three orders of
magnitude smaller in comparison with the two-step mechanism.Comment: 10 pages, Latex, 3 Postscript figure
Nuclear muon capture by 3He: meson exchange currents for the triton channel
Exchange current corrections are calculated using currents found from the
hard-pion model and AV14+3BF wavefunctions. Results are given for the rate and
spin observables. Their sensitivity to g_P, the nucleon pseudoscalar form
factor, is reported.Comment: 35 pages, uuencoded gz-compressed tar file 42 Kbyte
Final state interaction effects in mu-capture induced two-body decay of 3He
The mu-capture process on 3He leading to a neutron, a deuteron and a
mu-neutrino in the final state is studied. Three-nucleon Faddeev wave functions
for the initial 3He bound and the final neutron-deuteron scattering states are
calculated using the BonnB and Paris nucleon-nucleon potentials. The nuclear
weak current operator is restricted to impulse approximation. Large effects on
the decay rates of the final state interaction are found. The comparison to
recent experimental data shows that the inclusion of final state interactions
drastically improves the description of the data.Comment: 14 pages, 6 eps figure
Three-Nucleon Electroweak Capture Reactions
Recent advances in the study of the p-d radiative and mu-3he weak capture
processes are presented and discussed. The three-nucleon bound and scattering
states are obtained using the correlated-hyperspherical-harmonics method, with
realistic Hamiltonians consisting of the Argonne v14 or Argonne v18 two-nucleon
and Tucson-Melbourne or Urbana IX three-nucleon interactions. The
electromagnetic and weak transition operators include one- and two-body
contributions. The theoretical accuracy achieved in these calculations allows
for interesting comparisons with experimental data.Comment: 12 pages, 4 figures, invited talk at the CFIF Fall Workshop: Nuclear
Dynamics, from Quarks to Nuclei, Lisbon, 31st of October - 1st of November
200
Muon capture by 3He nuclei followed by proton and deuteron production
The paper describes an experiment aimed at studying muon capture by
nuclei in pure and mixtures at various densities. Energy distributions of
protons and deuterons produced via and are measured for the
energy intervals MeV and MeV, respectively. Muon capture
rates, and are obtained using two different analysis methods. The
least--squares methods gives , . The Bayes theorem
gives ,
. The experimental
differential capture rates, and , are compared with theoretical
calculations performed using the plane--wave impulse approximation (PWIA) with
the realistic NN interaction Bonn B potential. Extrapolation to the full energy
range yields total proton and deuteron capture rates in good agreement with
former results.Comment: 17 pages, 13 figures, accepted for publication in PR
The Axial-Vector Current in Nuclear Many-Body Physics
Weak-interaction currents are studied in a recently proposed effective field
theory of the nuclear many-body problem. The Lorentz-invariant effective field
theory contains nucleons, pions, isoscalar scalar () and vector
() fields, and isovector vector () fields. The theory exhibits a
nonlinear realization of chiral symmetry and has three
desirable features: it uses the same degrees of freedom to describe the
axial-vector current and the strong-interaction dynamics, it satisfies the
symmetries of the underlying theory of quantum chromodynamics, and its
parameters can be calibrated using strong-interaction phenomena, like hadron
scattering or the empirical properties of finite nuclei. Moreover, it has
recently been verified that for normal nuclear systems, it is possible to
systematically expand the effective lagrangian in powers of the meson fields
(and their derivatives) and to reliably truncate the expansion after the first
few orders. Here it is shown that the expressions for the axial-vector current,
evaluated through the first few orders in the field expansion, satisfy both
PCAC and the Goldberger--Treiman relation, and it is verified that the
corresponding vector and axial-vector charges satisfy the familiar chiral
charge algebra. Explicit results are derived for the Lorentz-covariant,
axial-vector, two-nucleon amplitudes, from which axial-vector meson-exchange
currents can be deduced.Comment: 32 pages, REVTeX 4.0 with 12pt.rtx, aps.rtx, revsymb.sty,
revtex4.cls, plus 14 figures; two sentences added in Summary; two references
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Effects of juvenile steelhead on juvenile chinook salmon behavior and physiology
Experiments were designed to determine whether and how steelhead Oncorhynchus mykiss affect chinook salmon O. tshawytscha when the two species are confined together. In a behavioral experiment, we observed groups of juvenile chinook salmon and steelhead together and groups of chinook salmon alone to determine whether the steelhead were aggressive and their presence changed the behavior of chinook salmon. We also performed two runs of a physiological experiment to determine whether the addition of steelhead to tanks containing chinook salmon would stress the chinook salmon, as determined by a change in their plasma cortisol levels. Behavioral changes were observed in the chinook salmon when they were held with steelhead; they reduced their movements, darted less, were attacked up to 16 times as often, and were found less frequently in the shade than chinook salmon held without steelhead. Steelhead were found to establish territories and defend them with chases, charges, and nips. In their attempts to establish and defend territories, the steelhead attacked the chinook salmon as often as they attacked other steelhead, but the chinook salmon showed little aggression toward the steelhead. Cortisol concentrations were significantly higher for chinook salmon in tanks receiving steelhead than in tanks receiving additional chinook salmon or no additional fish after 2 h (in one of the two experimental runs) and after 32 h (in both experimental runs; combined data). These results suggest that confining steelhead and chinook salmon together, such as in raceways and barges in the Columbia River system and in other situations, is stressful to the chinook salmon
Polarized photons in radiative muon capture
We discuss the measurement of polarized photons arising from radiative muon
capture. The spectrum of left circularly polarized photons or equivalently the
circular polarization of the photons emitted in radiative muon capture on
hydrogen is quite sensitive to the strength of the induced pseudoscalar
coupling constant . A measurement of either of these quantities, although
very difficult, might be sufficient to resolve the present puzzle resulting
from the disagreement between the theoretical prediction for and the
results of a recent experiment. This sensitivity results from the absence of
left-handed radiation from the muon line and from the fact that the leading
parts of the radiation from the hadronic lines, as determined from the chiral
power counting rules of heavy-baryon chiral perturbation theory, all contain
pion poles.Comment: 10 pages, 6 figure
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