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 pd→3HΛK+pd\to ^3H_\Lambda K^+ reaction cross section

The one- and two-step mechanisms of the $pd\to ^3H_\Lambda K^+$ 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 $pp\to d\pi ^+$ and $\pi^+n\to K^+\Lambda$ 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 $^3H_\Lambda$ wave function. The maximum value of the cross section is estimated as $\sim$1nb/sr. The contribution of the one-step mechanism with the elementary process $pN\to NK\Lambda$ 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 ${}^{3}\mathrm{He}$ nuclei in pure ${}^{3}\mathrm{He}$ and $\mathrm{D}_2 + {}^{3}\mathrm{He}$ mixtures at various densities. Energy distributions of protons and deuterons produced via $\mu^-+{}^{3}\mathrm{He}\to p+n+n + \nu_{\mu }$ and $\mu^-+{}^{3} \mathrm{He} \to d+n + \nu_{\mu}$ are measured for the energy intervals $10 - 49$ MeV and $13 - 31$ MeV, respectively. Muon capture rates, $\lambda_\mathrm{cap}^p (\Delta E_p)$ and $\lambda_\mathrm{cap}^d (\Delta E_d)$ are obtained using two different analysis methods. The least--squares methods gives $\lambda_\mathrm{cap}^p = (36.7\pm 1.2) {s}^{- 1}$, $\lambda_\mathrm{cap}^d = (21.3 \pm 1.6) {s}^{- 1}$. The Bayes theorem gives $\lambda_\mathrm{cap}^p = (36.8 \pm 0.8) {s}^{- 1}$, $\lambda_\mathrm{cap}^d = (21.9 \pm 0.6) {s}^{- 1}$. The experimental differential capture rates, $d\lambda_\mathrm{cap}^p (E_p) / dE_p$ and $d\lambda_\mathrm{cap}^d (E_d) / dE_d$, 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 ($\sigma$) and vector ($\omega$) fields, and isovector vector ($\rho$) fields. The theory exhibits a nonlinear realization of $SU(2)_L \times SU(2)_R$ 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 adde

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 $g_P$. 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 $g_P$ 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