应用光核反应计算μ原子中的核极化效应

近年来,瑞士保罗谢勒研究所的CREMA合作组通过测量$\mu$氢原子兰姆位移显著提升了质子半径的测量精确度。然而这一新实验结果与已知质子半径标准值(CODATA)相差5.6个标准差,被称为质子半径之谜,受到众多物理学家的关注。受此启发,CREMA合作组在不同的$\mu$原子中展开了一系列兰姆位移光谱的测量实验。他们计划从这些$\mu$原子的测量中得到轻核(包括$^{2,3}{\rm{H}}$,$^{3,4}{\rm{He}}$)的电荷半径。除了对光谱测量精度的要求外,轻核半径的实验精度当前仍被一项理论输入量限制:核极化效应对$\mu$原子光谱的修正。核极化效应体现了$\mu$子与原子核进行双光子交换中对核的虚激发,进而对$\mu$原子能谱产生高阶修正。因此,这一效应与光核反应以及康普顿散射直接相关。核极化效应对兰姆位移的修正可通过计算光核吸收截面以及虚光子康普顿振幅的求和规则而得到。本工作运用第一性原理的核结构计算方法,研究了$\mu$原子中的核极化效应。通过结合现代核力模型与超球简谐基展开多体方法,计算了一系列与核极化相关的光核反应及康普顿散射求和规则。这一理论研究为从$\mu$原子光谱测量中对核半径的精确提取提供了关键性的理论输入。     

Negative energy correction for nuclear polarization in muonic atoms

Negative energy corrections to the conventional calculations of nuclear polarization effects in muonic atoms are calculated. It is shown that the corrections are negligible as far as the NP effects due to low lying nuclear states and states in the giant resonance regions are concerned. However, the formula used for the muonic NP calculations breaks down if nuclear excitations with larger energies than the muonic mass are considered. This means that the method cannot be used for calculations of NP effects in electronic atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

High-energy,nuclear, and QED processes in strong laser fields

Various applications of ultraintense laser fields in particle physics, nuclear science, and quantum electrodynamics are presented. We discuss laser-driven lepton-pair creation, photon splitting, high-harmonic generation from both vacuum and muonic atoms, and direct nuclear excitation. All of these processes may come into experimental reach by near-future laser technology.     

Development Towards Muonic Atom Formation with Unstable Nuclei

We report on the latest development of a new method for extending muonic atom X-ray spectroscopy to the use of radioactive isotope beams to form muonic atoms with unstable nuclei. This would allow studies of the nuclear properties and nuclear sizes of unstable atoms by means of the muonic X-ray method at facilities where both negative muon and radioactive nuclear beams would be available. Progress of a feasibility study at RIKEN-RAL muon facility is also reported. This revised version was published online in August 2006 with corrections to the Cover Date.     

Precision measurements of nuclear quadrupole moments by muonic X-rays

The electric multipole hyperfine interaction in muonic atoms is discussed. In particular, the influence of the finite size of the nuclear electric multipole-charge distribution on the values of nuclear spectroscopic multipole moments that are extracted from muonic hyperfine measurements is considered. It is shown that nuclear electric quadrupole moments can be deduced from the observed hyperfine splittings of muonic M X-ray transitions with high precision and practically independently of the model nuclear quadrupole-charge density. Measurements of the ground-state electric quadrupole moments of 11 deformed nuclei in and near the rare-earth region are discussed.     

Challenge towards muonic atom formation with unstable nuclei

X-ray spectroscopy of muonic atoms is an important tool to obtain information on the nuclear charge distribution of nuclei. It has been successfully used for many years to study stable isotopes in condensed or gaseous states. A new method has been proposed to extend muonic atom X-ray spectroscopy to the use of radioactive isotope beams to form muonic atoms with unstable nuclei. This new method allows studies of the nuclear properties and nuclear sizes of unstable atoms by means of the muonic X-ray method at facilities where both negative muon and radioactive nuclear beams would be available. Progress of a feasibility study at RIKEN-RAL muon facility is also reported. Received: 1 May 2001 / Accepted: 4 December 2001     

Muonic atoms testing the electron propagator of quantum electrodynamics and the Higgs boson contribution

In this work we consider the energy states of muonic atoms which are predominantly influenced by vacuum polarization. This fact is used for testing the electron propagator of QED with the modification \(S(p) = (\not p - me)^{ - 1} + f(\not p - M)^{ - 1}\) . The data of some well analyzed transitions in muonic He, Si, Ba, and Pb yield the limit M>29 MeV for f=1. Similarly the presence of a Higgs boson would cause a shift of the energy levels which can be measured easier in muonic atoms since the coupling grows with the fermion mass. The analysis of several transitions in heavy muonic atoms shows, that the mass of the Higgs boson is larger than 12.8 MeV. Further reductions of the present-day uncertainties concerning the experimental data and especially of the nuclear structure effects could improve these limits.     

Neutral current effects in muonic atoms: E1-E2 interferences

We study the parity-violating neutral current effects in muonic atoms which might result from an interference between E1 and E2 amplitudes in 3D → 1S transitions. We conclude that polarization asymmetries may be measurable in heavy atoms (Z ~ 70) exhibiting large nuclear deformations.     

Update on nuclear structure effects in light muonic atoms

We present calculations of the nuclear structure corrections to the Lamb shift in light muonic atoms, using state-of-the-art nuclear potentials. We outline updated results on finite nucleon size contributions.     

Proposal for X-ray spectroscopy of muonic atoms formed from implanted ions in solid hydrogen films

A new method is proposed to extend muonic atom X-ray spectroscopy to the study of nuclear beams, including radioactive beams, by stopping both muon and nuclear beams in a solid hydrogen film. The muon transfer reaction to higher Z nuclei is used then to form muonic atoms. This method would allow studies of the nuclear charge distribution of unstable atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Hyperfine structure of light exotic atoms

Recoil corrections to the hyperfine structure of light exotic atoms, including the effect of the anomalous magnetic moment are calculated for light muonic and baryonic atoms. In the case of muonic atoms, the effects of recoil and finite nuclear size are significant in view of the presently attainable experimental precision.     

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     

Parity violation correlations in light muonic atoms

The 2S-1S transition in light muonic atoms is very sensitive to parity violation correlations induced via neutral currents. Observables depending on these transitions such as the photon polarization and the angular correlation between the emitted radiation and the atom polarization are a clear signal of weak neutral currents in atoms. We find the relation between the lepton and quark couplings and these observables emphasizing the effect of the nuclear spin. The results expected in muonic, atoms μ-⁴He and μ-³He are given.     

Muonic molecules in superintense laser fields

We study theoretically the ionization and dissociation of muonic molecular ions (e.g., dd mu) in superintense laser fields. We predict that the bond breaks by tunneling of the lightest ion through a bond-softened barrier at intensity I > or =10(21) W/cm(2). Ionization of the muonic atomic fragment occurs at much higher intensity I > or =6 x 10(22) W/cm(2). Since the field controls the ion trajectory after dissociation, it forces recollision of a approximately 10(5)-10(6) eV ion with the muonic atom. Recollision can trigger a nuclear reaction with sub-laser-cycle precision. In general, molecules can serve as precursors for laser control of nuclear processes.     

Nuclear excitation and isomer shifts in muonic atoms: (II). Model-independent parametrization and discussion

Excitation probabilities and isomer shifts for about 50 excited nuclear levels from muonic atoms of Sm, Gd, Eu, Tm, Yb, Ta, W, Re, Os, Ir, Pt, Hg, Tl, and Bi are discussed. The data for ¹⁵³Eu are used in comparison with isomer shifts from the Mössbauer technique to evaluate electron density differences in rare earth compounds. Mössbauer and muonic isomer shifts are sensitive to different moments of the change of the charge distribution. Therefore, from a comparison new information can be deduced. The results of the muonic isomer shifts are compared with calculations based on various nuclear models.     

Laser polarized muonic atoms

Lasers are an important tool in the field of muon physics. A new application of lasers, namely producing polarized muonic atoms, is the subject of a new program at LAMPF. One technique already demonstrated is stopping unpolarized muons in a laser polarized³He target. A more promising idea is to polarize neutral muonic helium by collisions with laser polrized Rb vapor. These methods for producing polarized muonic helium will be useful for measuring the spin dependence of nuclear muon capture and for determining the induced pseudoscalar coupling.     

Correlation between muonic levels and nuclear structure in muonic atoms

A method that deals with the nucleons and the muon unitedly is employed to investigate the muonic lead, with which the correlation between the muon and nucleus can be studied distinctly. A “kink” appears in the muonic isotope shift at a neutron magic number where the nuclear shell structure plays a key role. This behavior may have very important implications for the experimentally probing the shell structure of the nuclei far away from the β-stable line. We investigate the variations of the nuclear structure due to the interaction with the muon in the muonic atom and find that the nuclear structure remains basically unaltered. Therefore, the muon is a clean and reliable probe for studying the nuclear structure. In addition, a correction that the muon-induced slight change in the proton density distribution in turn shifts the muonic levels is investigated. This correction to muonic level is as important as the Lamb shift and high order vacuum polarization correction, but is larger than anomalous magnetic moment and electron shielding correction.     

The nuclear size correction to the energy levels of the light hydrogen-like and muonic atoms

A closed form expression for the nuclear size correction to the energy of the S states of the light hydrogen-like and muonic atoms is obtained in the second- and third-order perturbation theory.     

Difference in the electronic and fission decay modes for muonic atoms

A simple model is presented which predicts a difference in the electronic and fission decays of ground-state muonic heavy atoms. It is interpretable in terms of the relative population of two nuclear states: the isomeric fission state and the ground state. The application of the model to ²³⁸U indicates there could be a significant population of the isomeric state at the end of the muonic atomic cascade.     

Penetrability of nuclear fission barrier for muonic atoms

The nuclear fission penetrability for muonic atoms is calculated as a function of excitation energy. The results obtained for ^234,236,238U and ²⁴⁰Pu are compared with the fission of normal atoms.