Neutron-neutron interaction and possible off-shell effects in muon capture by deutrons

Dramatic changes in the doublet transition rates have been found due to the off-shell effects in a class of phase-shift-equivalent potentials. The comparison of potential approach with the Omnès-Muskhelishvili method is performed.     

Gamma-rays following muon capture

The energy and intensity of γ-rays following capture of muons by Si, Ti, Mn, Fe, Co, Ni, Y, Ag and Au were measured with a Ge(Li) detector. In most cases it was possible to identify the final nucleus from the energy of the γ-ray observed. In general, this showed that one or more neutrons were emitted in the initial stages of de-excitation. In the case of capture by Fe and Ni the evidence pointed to a mode of de-excitation by the emission of a proton and a neutron and in Ti by γ-rays alone. In these measurements it was possible to account for as much as 60% of the muons captured in Co, less in the other elements, and only 15 % in Si.     

Kinematical and dynamical considerations of muon capture by deuteron

Proton inducedL X-ray yields from thick targets of In, Sn, Nd, Dy, Pt and Au have been measured in the energy range 1–3 MeV. Cross-sections have been derived from these thick target yields and are compared with the predictions of non relativistic PWBA, BEA and CBEA theories. The ratios σ_Lα/σ_Ll, σ_Lα/σ_Lβ and σ_Lα/σ_Lγ are also presented.     

Neutron asymmetry in muon capture by few-nucleon systems

Importance of the velocity dependent terms upon the form of the energy dependence of the neutron asymmetry in muon capture by deuterons is demonstrated.     

Radiative muon capture on nuclei

Radiative muon capture rates of stopped meons, spectra, circular polarisation, and asymmetries of emitted -quanta in¹⁶O and⁴⁰Ca are analysed using the shell-model nuclear wave functions. Calculated characteristics show considerable sensitivity to the value of induced pseudoscalar coupling constantg _p. Where possible we compare the theoretical results with the preliminary experimental data.Dedicated to the 25th anniversary of the Joint Institute for Nuclear Research.On leave of absence fromthe Institute of Nuclear Physics, Czechosl. Acad. Sci., 250 68 e, Czechoslovakia.     

Spin-isospin excitations and nuclear muon capture

Muon capture rates in complex nuclei are calculated on basis microscopic models of nuclear structure. The calculation results are consistent with experimental values, unsuppressed spin-isospin transitions, and in contrast to the data obtained from the cross sections for nuclear charge-exchange (p, n) and (n, p) reactions.     

Radiative muon capture on hydrogen

The radiative capture of negative muons by protons can be used to measure the weak induced pseudoscalar form factor. Brief arguments why this method is preferable to ordinary muon capture are given followed by a discussion of the experimental difficulties. The solution to these problems as attempted by experiment #452 at TRIUMF is presented together with preliminary results from the first run in August 1990. An outlook on the expected final precision and the experimental schedule is also given. Talk presented by W. Bertl at the Symposium “The Future of Muon Physics” in Heidelberg, Germany, May 7–9, 1991     

Configuration mixing and total muon capture rates

We modify the Primakoff closure approximation to get independence on the mean neutrino energy and energy weighted sum rules are used for the corrective terms. A near model - independent discussion is then possible, and the total rates are shown to be a very sensitive tool to investigate configuration mixing of the target. Wild discrepancies with experiment would arise if the limit of pure jj or LS couplings are used for ¹²C, whereas the Cohen-Kurath wave function gives a very good result.     

Energetic neutrons from muon capture by a heavy nucleus

The spectrum of energetic neutrons observed in a recent experiment on $\text{μ}{}^{\mathrm{?}}\text{+}{}^{165}\text{H}{}_0\text{→ n + X + ν}{}_{\mathrm{\mu }}$ is discussed using a simple model. It is found that the neutron spectrum can be reproduced reasonably well in terms of the nuclear Fermi motion deduced from other sources of information such as high-energy heavy-ion collisions.     

Nuclear orientation following muon capture by spin zero nuclei

It is shown that in the proposed experimental set-up of the Louvain-Saclay collaboration, the nuclei recoiling into the forward (or backward) hemisphere in the reaction $\text{μ}{}^{\mathrm{?}}\text{+ A(J}{}_{\mathrm{<mtext>i</mtext>}}\text{= 0) → B(J}{}_{\mathrm{<mtext>f</mtext>}}\text{≧ 1) + ν}{}_{\mathrm{\mu }}$ will not only be polarized but also aligned. A general expression for the alignment of the recoiling nucleus is derived in terms of the other observables and it is shown to be independent of nuclear structure and the dynamics of the muon capture interaction. Numerical results are presented for muon capture by ¹²C and ¹⁶O.     

Precision measurement of nuclear muon capture by3He

In this article we report the results of an experiment performed in 1993 at PSI. The goal was to determine the absolute rate of nuclear muon capture by³He. In the experiment we used a new technique recently developed at Gatchina. As a preliminary result from this experiment we obtained _c=(1496±3(stat)-3(syst)) s^–1.     

Electroweak radiative corrections to muon capture

Electroweak radiative corrections to muon capture on nuclei are computed and found to be sizable. They enhance the capture rates for hydrogen and helium by 2.8% and 3.0%, respectively. As a result, the value of the induced pseudoscalar coupling, g(P)(exp), extracted from a recent hydrogen 1S singlet capture experiment is increased by about 21% to g(P)(exp)=7.3+/-1.2 and brought into good agreement with the prediction of chiral perturbation theory, g(P)(theory)=8.2+/-0.2. Implications for helium capture rate predictions are also discussed.     

Radiative muon capture in medium-heavy nuclei

Radiative muon capture in nuclei is thoroughly investigated in view of its sensitivity to the pseudoscalar coupling constant g_P. In the photon energy domain of interest (k ? 60 MeV) the effective one-body hamiltonian in use is shown essentially to hold true, with minor corrections due to the muon propagator in the nuclear field and to the two-step process. The closure approximation is avoided by appropriately integrating the response function calculated in the Fermi gas model, in the energy-momentum transfer plane.Theoretical predictions in medium-heavy nuclei of the high-energy photon spectrum, of photon polarization, and of muon-spin photon angular correlation are given for various values of the pseudoscalar coupling constant.     

Angular correlation for nuclear muon capture

Formulae for the capture rates, gamma-neutrino correlations, and angular distributions of recoil in muon capture processes J_i J_f by an unpolarized nucleus for J_i ≦ 3 and J_f ≦ 5/2, with and without change of parity of nuclear levels, are given explicitely in terms of the multipole amplitudes. Relation of helicity amplitudes for muonic atom decay to the multipole amplitudes and to amplitudes introduced by other authors is presented. The derivation is based on kinematics only, and the formulae are strictly valid for the muon capture by any nuclei. The formulae are convenient for model calculations of partial transitions with realistic nuclear and muon wave functions and for the phenomenological analysis of a weak interaction.     

Negative muon capture in3He

We compute the partial capture rate of negative muons in³He by following the analysis of Peterson to include the relativistic corrections and the exchange effects, for various values of theg _p /g _A ratio. We also calculate the total capture rate. The ground state of³He is assumed to be spherical. The radial dependence of the ground state wave function is taken to be (a) one parameter Irving function, (b) a modified three-parameter Irving function and (c) a function having ‘soft-core’, whose parameters have been fixed in a variational calculation of the binding energy of the triton using a non-local momentum-dependent potential involvingp ² terms. The calculated values of the capture rates are compared with the experimental data to find a value for theg _p /g _A ratio.     

High-multiplicity neutron emission from muon capture

The nuclear excitation function resulting from muon captures on pairs of nucleons which is induced by meson-exchange currents, is used to calculate the probabilities of high-multiplicity (X⩾6) neutron emission. For muon capture in ²⁰⁹Bi these are found to be 8 × 10⁻³ for X = 6, 3.5 × 10⁻³ for X = 7 and 0.7 × 10⁻³ for X = 8. Results are presented also for Pb, Ho and Ag. The agreement with existing experiments is very good.     

Induced pseudoscalar interaction in weak nucleon current and muon capture in hyperfine states of muonic deuterium

Muon capture rate in muonic deuterium can be calculated with less ambiguities in nuclear wave functions, since we know the bound and scattering states of the two nucleons with higher accuracy theoretically. It is, however, dependent on the pion-nucleon-delta coupling constant through the exchange current effect. This dependence is considerably reduced for the ratio of the capture rates from two hyperfine states of muonic deuterium. This ratio is, therefore, useful to study the strength of the induced pseudoscalar term. Several other physical quantities in light nuclei are also introduced here for the same purpose.     

Ordinary and radiative muon capture in complex nuclei

The total rates of ordinary and radiative muon capture in natural zirconium and molybdenum are calculated within the quasiparticle random phase approximation. The total ordinary-muon-capture rates calculated with the unquenched weak axial-vector coupling are consistent with the experimental data and weakly depend on the weak pseudoscalar coupling. The calculated radiative-muon-capture rates have a clear dependence on the pseudoscalar coupling, but highly overestimate the experimental data. The text was submitted by the authors in English.     

The vanishing cabibbo angle and muon capture rates

Recent papers have discussed the possibility that a spontaneously broken symmetry is restored at high magnetic fields. We note possible evidence in favour of this idea.