Neutrino disintegration and muon capture in the deuteron

Neutrino and antineutrino disintegration of the deuteron and muon capture in the deuteron are studied. The final-state interaction between the nucleons is considered. The two-nucleon final state is found for the realistic potentials suggested by Reid and Ulehla et al.     

Effect of correlations on nuclear muon capture

The process μ⁻+¹²C→¹²B+v _μ is studied using the modified Hartree Fock wavefunction obtained with the unitary-model-operator-approach starting from the realistic hardcore nucleon-nucleon interaction, with the aim of testing the wavefunctions and obtaining a numerical value for the induced pseudoscalar coupling constant (g _P ). These observables, namely, the partial capture rate to the¹²B(1⁺; g.s), its recoil nuclear polarisation and the total capture rate, which exhaust the available experimental data in the above process have been calculated and compared with the other theoretical and experimental results. As far as the partial capture rate is concerned the use of the unitary-model operator approach wave functions for¹²C withb=2.09 fm and Cohen-Kurath wave function for¹²B(1⁺; g.s) reduces the pure shell model capture rate by about 30%. The effect of strong configuration mixing in the ground state of¹²C in taken into account by introducing a scale factor ξ similar to the ‘amplitude reduction factor’ of Donnelly and Walecka. With this ξ the agreement with the experiment both for the partial capture rate and the beta decay ‘ft’ value is found to be satisfactory. The¹²B(1⁺; g.s) recoil polarisation is found to be insensitive to the use of the unitary-model-operator-approach wave functions. When compared with the experimental data, we obtaing _P =(14.9±1.9)g _A . The total capture rate is found to be sensitive to the use of the unitary-modeloperator-approach wave functions which contain the effect of nucleon-nucleon short range correlations and we obtain a satisfactory agreement with the experiment for¹⁶O and¹²C, thereby revealing the importance of the effect of such correlations in the total capture rate studies.     

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.     

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.     

Time reversal test in the nuclear muon capture

Possible effects of breaking CP-symmetry are looked for in the muon capture by a linearly polarized target nucleus. With this aim the recoil polarization in the partial transitions \(0\xrightarrow{{\mu ^ - }}I,1/2\xrightarrow{{\mu ^ - }}J\) and \(1\xrightarrow{{\mu ^ - }}I\) is investigated in a nuclear model independent way. It is shown that the hyperfine structure of the muonic atom significantly influences theT-odd correlations in the recoil polarization formula, and the expectation for theT- odd signal in case of the linearly polarized target is higher by one order of magnitude. We obtain the complete set of theT-odd observables which could enter the polarization formula. As an example, within the impulse approximation for the weak interaction hamiltonian, we analyse the nonstandard, CP-breaking extension of the Fermi theory using complex Fujii-Primakoff form factorG _V e^iφ .     

Effects of kinematical constraints in nuclear muon capture

Muon capture is discussed in the framework of linear response theory. This approach allows a general discussion of the role played by kinematical constraints in determining which features of nuclear dynamics are actually probed in the capture event. It is argued that the muon momentum spread can increase the capture rate at large energy transfer.     

The nuclear excitations and particle emission following muon capture

The nuclear muon capture process is studied as an excitation of the analogues of various harmonics of the multipole giant resonance. The excitation energy distribution is calculated with the use of the hydrodynamical model of the nucleus. The following particle emission cascade (including precompound states) is considered and the obtained particle spectra as well as yields of various residual nuclei are in a fair agreement with the existing experimental data.     

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.     

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.     

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     

Symmetry tests within the Standard Model and beyond from nuclear muon capture

Precision measurements in nuclear muon capture on the proton and ³He allow for tests of the Standard Model for the strong and electroweak interactions, complementary to those achieved in high energy experiments. The present situation and future prospects are reviewed, emphasizing where renewed efforts could prove to be rewarding in exploring ever further beyond the confines of the Standard Model. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Effects of exchange currents on muon capture

It is shown that the one-pion exchange current renormalizes the axial and induced pseudoscalar form factors of the weak axial current. The effect decreases total muon capture rate about 13% and the branching ratio of radiative-to-ordinary muon capture rate about 12%.     

Continuity-equation constraint in the two-vertex nuclear processes: Radiative muon capture on 16O and 40Ca

A modified form of the impulse-approximation effective hamiltonian of the nuclear radiative muon capture (RMC) is developed. In the derivation we have used the electromagnetic current-continuity equation; the procedure is actually an extension for the nonzero momentum transfer of the Siegert theorem. Radiative capture rates and spectra of the emitted photons for RMC on ¹⁶O and ⁴⁰Ca are analysed by using the nuclear shell-model wave functions for the calculation of the partial RMC transition rates. The spectra obtained are strongly reduced in comparison with the standard impulse-approximation calculations and agree with the phenomenological results. The main contradiction of recent RMC theoretical works has been resolved in this way.     

Measurement of the breakup channels in nuclear muon capture by3He and4He

The rates of the breakup reactions _B(³He) and _B(⁴He) in nuclear muon capture by³He and⁴He have been measured. The measurements were performed on the muon beam of PSI with a multi-anode high-pressure ionization chamber filled with isotopically pure³He or⁴He at 120 bar. The chamber was used as a target and detector for both the incoming muons and for the charged reaction products (tritons, deuterons and protons) of the breakup reactions _B(³He) and _B(⁴He). Our statistics, about 5 × 10⁵ of breakup events, provides a possibility to improve the precision of evaluated rates. The preliminary results: _B(³He)=720 ± 70 s^–1, _B(⁴He)=415 ± 40 s^–1 are compared to theoretical predictions and to previous experiments.     

Recoil nuclear polarization in muon capture—Effect of target thickness and finite range of nuclear recoils

The effect of target thickness and finite range of nuclear recoils is investigated in the study of average and longitudinal polarizations of recoiling nuclei resulting from the capture of muons by spin zero target nuclei.     

Neutrino mass anarchy

What is the form of the neutrino mass matrix which governs the oscillations of the atmospheric and solar neutrinos? Features of the data have led to a dominant viewpoint where the mass matrix has an ordered, regulated pattern, perhaps dictated by a flavor symmetry. We challenge this viewpoint and demonstrate that the data are well accounted for by a neutrino mass matrix which appears to have random entries.     

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.