Dynamics of muonic atom cascade in hydrogen-helium mixtures

The deexcitation of excited muonic protium and deuterium in the mixture of hydrogen and helium isotopes is considered. Methods of experimental determination of the probability of direct atomic muon capture by hydrogen and muon transfer rates from excited muonic hydrogen to helium are proposed. Theoretical results for the population of the muonic atoms in the ground state, , are compared with the existing experimental data. Results obtained for mixtures are of interest for investigation of nuclear fusion in muonic molecules. Received: 6 August 1998 / Revised: 1st October 1998 / Accepted: 2 October 1998     

Laser influence on positron-antiproton radiative capture collision

The laser-assisted radiative capture between a positron and an antiproton is studied in detail. The theoretical results show that the cross-section for antihydrogen formation is significantly reduced with the application of a laser background. This effect is most marked when the laser polarization is parallelto the incident direction. Received: 13 November 1998 / Received in final form: 16 March 1999     

Charge transfer from the ground state of muonic hydrogen to at room temperature

The present status of research of muon transfer from the ground state of muonic protium to ⁴He is reviewed. The analysis of a recent measurement in a triple gas mixture of H₂+⁴He+Ne at 15 bar and room temperature is presented and the result is compared to the existing experimental and theoretical rates. The average muon transfer rate from protium to ⁴He determined from all lifetime measurements is . Received: 22 January 1998 / Revised: 4 March 1998 / Accepted: 31 March 1998     

Towards a better understanding of O nuclear structure: Muon capture and radiative pion capture reactions

Muon capture and radiative pion capture reactions on ¹⁶O have been analysed with the aim to extract more information on the importance of higher components of the A = 16 nuclear ground and excited states. Good agreement with the experimental data for both reactions may be achieved if at least 2p2h components of the nuclear wave functions are taken into account. The positive parity excited states in ¹⁶N are shown to contribute 43 % to the radiative π⁻ capture but only ≈ 10 % to the muon capture rate.     

Energy spectra of neutrons emitted following muon capture in O and C

The energy spectra of neutrons emitted following muon capture in ¹⁶O and ¹²C are investigated using the continuum shell model. Nuclear wave functions, which have been shown by Ohtsubo and the author to describe the radiative pion capture reaction in the above nuclei well, are adopted. The calculated neutron energy spectra explain well the observed main peaks, at 5 MeV for ¹⁶O and 4 MeV for ¹²C, which are considered to be the giant resonances excited in the muon capture reaction. These peaks are interpreted as the 2⁻ state at 20.3 MeV for ¹⁶O and the 1⁻ state at 22.5 MeV for ¹²C. Comparisons with photon spectra in radiative pion capture reactions are also made. The calculated total capture rates exceed the experimental values by a factor of 2.5 for ¹⁶O and by 30–40% for ¹²C.     

Inelastic cross-sections and natural lifetimes for the 62D3/2, 5/2 and 82S1/2 states of Rb

The results of an experimental study of population dynamics following excitation of [0pt] and [0pt] states of rubidium are reported. Excitation transfer and quenching cross-sections in collisions with ground state rubidium atoms, and natural lifetimes have been measured. The experiment was performed in a vapour cell, using pulsed two-photon excitation and photon counting detection. The analysis of time dependent signals was based on a rate equation model in which transitions induced by thermal radiation have been accounted for. The measurements yielded following results: (1) [0pt] state J-mixing cross-section: [0pt] ; (2) cross-sections for [0pt] excitation transfer process: [0pt] ; (3) quenching cross-sections: [0pt] , [0pt] , [0pt] ; [0pt](4) radiative lifetimes: [0pt] ns, [0pt] ns, [0pt] ns. Received 1st December 1998 and Received in final form 17 May 1999     

Hard meson corrections to the amplitude for radiative muon capture and the elementary particle method

Hard meson corrections to the amplitude of radiative muon capture on the proton are derived within the framework of vector meson dominance in the tree approximation. The weak form factors are mediated by π, ρ and A₁ mesons which may radiate. The model reproduces the terms in the amplitude of lower order in the momentum transfers as derived from low-energy theorems and determines higher-order terms which are otherwise ambiguous or undetermined. Arguments are given why a similar approach to radiative muon capture in nuclei in an elementary particle method is expected to fail.     

Multi-phonon capture of charge carriers by dislocation kinks in semiconductors

In view of the problem of recombination-enhanced motion of dislocations in semiconductors, we studied the thermal capture of an electron by a smooth dislocation kink. Multi-phonon capture becomes possible due to localization of the carrier on the kink. The localized state on the smooth kink is studied in the deformation potential approximation. In this case the potential created by the kink is described by Poschl-Teller function, which enables to find the analytical expressions for the eigenstates and the corresponding wave functions. With the use of the ground state wave function we find the multi-phonon capture cross-section for two limiting temperature cases, corresponding to the thermally activated and quantum transitions between vibronic terms.     

Hard meson corrections to the amplitude for radiative muon capture and the elementary particle method

Hard meson corrections to the amplitude of radiative muon capture on the proton are derived within the framework of vector meson dominance in the tree approximation. The weak form factors are mediated by π, ρ and A₁ mesons which may radiate. The model reproduces the terms in the amplitude of lower order in the momentum transfers as derived from low-energy theorems and determines higher-order terms which are otherwise ambiguous or undetermined. Arguments are given why a similar approach to radiative muon capture in nuclei in an elementary particle method is expected to fail.     

Chiral Lagrangians and the Transition Amplitude for Radiative Muon Capture

 The transition operator for the radiative capture of mesons by protons is constructed starting from a chiral Lagrangian of the system obtained within the approach of hidden local symmetries. The transition operator is gauge invariant and its hadron radiative part satisfies exactly two relevant continuity equations. Received October 16, 1998; accepted for publication February 23, 1999     

Intermediate energy bremsstrahlung and the structure of free and bound hadrons: Radiative pion proton scattering,pion decay and muon capture

Experimental data on pion-proton bremsstrahlung, radiative pion decay and radiative muon capture are reviewed to demonstrate that the study of intermediate energy bremsstrahlung processes can reveal additional information on hadron structure inaccessible in their non-radiative counterparts.Dedicated to the memory of M. Gmitro.     

Investigation of magneto-optical effect in transverse magnetic field in He

The non-linear Voigt effect has been studied in He discharge under resonance laser interaction with the He transition. The range of non-linear signal existence was determined. The contribution of the lower and upper states to the overall signal was analyzed. The cross-section for depolarizing collisions with ground state He atoms was estimated for the 3³ D _2,3 He state. Received: 16 June 1998 / Received in final form: 14 December 1998     

Giant magnetic dipole analog excitations by the allowed muon capture in 1p-shell nuclei

The distributions of the allowed muon capture strengths in 1p-shell nuclei are shown to exhibit a tendency to concentrate in a few low-lying daughter states. These strong excitations are analogs of the giant magnetic dipole transitions, predicted by Kurath, and observed in inelastic electron scattering. Similar excitations are expected in 1S radiative pion capture and low-energy charged pion photoproduction processes.     

CdH分子基态X~2∑~+和激发态A~2П光谱和寿命测量

采用一束激光为泵浦光另一束激光为探测光的方法,获得CdH分子A~2Π态和X~2∑~+态之间跃迁产生的具有转动结构的多个荧光谱和激发谱带.对荧光的时间分辨研究,给出A~2Π态寿命τ_0=59.5±2.3ns,对A~2Π(v=0)态Cd原子的碰撞猝灭截面为(1.31±0.03)×10~(-15)cm~2;X~2∑~+态寿命τ_0=61.0±4.6μs,引起X~2∑~+(v=0)态寿命衰减的碰撞截面为(1.1±0.1)×10~(-18)cm~2.     

Equivalence between local Fermi gas and shell models in inclusive muon capture from nuclei

Motivated by recent studies of inclusive neutrino nucleus processes and muon capture within a correlated local Fermi gas model (LFG), we discuss the relevance of nuclear finite-size effects in these reactions at low energy, in particular for muon capture. To disentangle these effects from others coming from the reaction dynamics we employ here a simple uncorrelated shell model that embodies the typical finite-size content of the problem. The integrated decay widths of muon atoms calculated with this shell model are then compared for several nuclei with those obtained within the uncorrelated LFG, using in both models exactly the same theoretical ingredients and parameters. We find that the two predictions are in quite good agreement, within 1-7%, when the shell model density and the correct energy balance is used as input in the LFG calculation. The present study indicates that, despite the low excitation energies involved in the reaction, integrated inclusive observables, like the total muon capture width, are quite independent of the fine details of the nuclear wave functions. An erratum to this article is available at .     

Resonant scattering of an electron by a muon in the field of light wave

In the frame of the Born approximation we theoretically investigate resonant scattering of an electron by a muon in the field of elliptically polarized electromagnetic wave in the general relativistic case. It is studied kinematics of a scattering of an electron in resonant region. It is derived the expressions for the amplitude and the cross-section of the resonant scattering of an electron by a muon when the invariant intensity parameter of the laser field is small (η_e ≪1). It is demonstrated that the resonant cross-section of a scattering may be several orders of magnitude higher than the cross-section of a scattering in the absence of the external field.     

Ortho-para transition rate in mu-molecular hydrogen and the proton's induced pseudoscalar coupling gp

We report a measurement of the ortho-para transition rate in the p mu p molecule. The experiment was conducted at TRIUMF via the measurement of the time dependence of the 5.2 MeV neutrons from muon capture in liquid hydrogen. The measurement yielded an ortho-para rate Lambda op = (11.1 +/- 1.7 +/-(0.9)(0.6)) x 10(4) s(-1), which is substantially larger than the earlier result of Bardin et al. The result has striking implications for the proton's induced pseudoscalar coupling g(p), changing the value of g(p) obtained from the most precise ordinary muon capture measurement from 10.6 +/- 2.7 to 0.8 +/- 2.8, and from the sole radiative muon capture measurement from 12.2 +/- 1.1 to 10.6 +/- 1.2, bringing the latter result closer to theoretical predictions.     

Interaction versus dimerization in one-dimensional Fermi systems

In order to study the effect of interaction and lattice distortion on quantum coherence in one-dimensional Fermi systems, we calculate the ground state energy and the phase sensitivity of a ring of interacting spinless fermions on a dimerized lattice. Our numerical DMRG studies, in which we keep up to 1000 states for systems of about 100 sites, are supplemented by analytical considerations using bosonization techniques. We find a delocalized phase for an attractive interaction, which differs from that obtained for random lattice distortions. The extension of this delocalized phase depends strongly on the dimerization induced modification of the interaction. Taking into account the harmonic lattice energy, we find a dimerized ground state for a repulsive interaction only. The dimerization is suppressed at half filling, when the correlation gap becomes large. Received: 11 February 1998 / Revised: 1st April 1998 / Accepted: 30 April 1998     

μ-介子在He3原子核上的俘获

本文计算了μ介子在He³核上俘获的几率、末态H³核的角分布和极化。所采用的理论是带有重正化效应(包含弱磁矩及赝标项)的V-A普适弱作用理论。在计算中考虑了μ和He³核在始态有极化及处于不同超精细态上的情况。在计算中假定了He³核的基态是纯S态,这时忽略了由张量力以及其他自旋轨道耦合力引起的其他态。介子交换电流的效应也没有考虑。在以上这两个假定下,我们证明了俘获几率中只包含一个未知的原子核矩阵元,这个矩阵元恰好是原子核密度函数的富氏分量。利用μ介子(或电子)与He³(或H³)原子核的散射可以确定这个未知矩阵元。     

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.