Keh-Ning Huang

Constraining neutrino electromagnetic properties by germanium detectors

The electromagnetic properties of neutrinos, which are either trivial or negligible in the context of the Standard Model, can probe new physics and have significant implications in astrophysics and cosmology. The current best direct limits on the neutrino millicharges and magnetic moments are both derived from data taken with germanium detectors with low thresholds at keV levels. In this paper, we discuss in detail a robust, ab initio method: the multiconfiguration relativistic random-phase approximation, that enables us to reliably understand the germanium detector response at the sub-keV level, where atomic many-body physics matters. By using existing data with sub-keV thresholds, limits on the reactor antineutrinos millicharge, magnetic moment, and charge radius squared are derived. The projected sensitivities for next-generation experiments are also given and discussed.

Doubly excited states of the Be atom in the MCRRPA

Photoionization parameters in neutral beryllium are calculated in the multiconfiguration relativistic random-phase approximation to resolve the interplay between relativistic and correlation effects in low-Z atoms or ions. Precise energies and widths of all five Rydberg series of low-lying doubly excited states (2pns)3,1Po1, (2pnd)3,1Po1 and (2pnd)3Do1 are given. Experimental studies on angular distribution of photoelectrons are suggested to obtain information on widths of some states, which cannot be obtained from total cross-section measurements.

Applications of the relativistic equation of motion to photoionization of Mg-like ions

Abstract As an approximation to the relativistic equation of motion, the multiconfiguration relativistic random-phase approximation theory is applied to the valence-shell photoionization of the Mg-like ions. Photoionization cross sections between ( 2 p 6 3 s ) 2 S 1 / 2 and ( 2 p 6 3 p ) 2 P 1 / 2 0 ionization thresholds are calculated. The main feature of our results is exhibited by five Rydberg series of doubly excited states arising from fine-structure splittings. A comparative study of Al + , Si 2+ , P 3+ , S 4+ , Cl 5+ , and Ar 6+ is presented.

Symmetries and polarization correlations in collision processes

A unified quantum collision theory for an elementary reaction is reviewed in the wave-packet approach. General kinematic analyses of various atomic collision processes by using the density-matrix and helicity formulations are presented. The rotation, parity, and time-reversal symmetries of the colliding system are considered. In addition to polarization and angular correlations in each collision process, correspondences among different collision processes are also studied. These symmetry studies in atomic collisions provide a great deal of valuable information about the colliding systems and enhances our knowledge on the collision dynamics.

Core-polarization effects in the 3P1o1P1o separations of Cd- and Hg-like ions☆

Abstract The 3P1o1P1o separations of Cd- and Hg-like ions from the multiconfiguration relativistic random-phase approximation including core-excitation channels are compared with those from other theories and with experiment. The present ab initio results are generally in better agreement with experiment than those from semiempirical theories.

Angular and polarization correlations in double-excitation resonances of Mg

Angular distribution and spin polarization of photoelectrons from 3s valence subshell of neutral magnesium are investigated by using the multiconfiguration relativistic random-phase approximation. Photoionization parameters for all five Rydberg series of double-excitation resonances P1o, P1o, and 3D1o between the Mg+[3s] and Mg+[3p] thresholds are presented to clarify the high-energy portion of the Rydberg series, in which peaks corresponding to double excitations can be identified unambiguously.

Impact-Ionization Processes in Fusion Plasmas

Starting from the relativistic equation of motion governing quantum collision processes in many-particle systems, we shall formulate the relativistic quantum collision theory in an ab initio manner. Quantum electrodynamic effects are however in corporated perturbatively. Because heavy projectiles or ultra-high incident energies are considered, the recoil of the target is also treated. Electron-impactionization of uraniumion U91+ and proton-impactionization of hydrogen will be given as examples.

Photoionization Processes of the Single-Ionized Boron

The relativistic calculations of the cross-section , the angular-distribution parameter , and spin-polarization parameters of photoelectrons using the multiconfiguration relativistic random-phase approximation theory for the photoionization of the ion are presented. Precise energies and widths of all five Rydberg series of doublyexcited states , , , , and are determined. Our predictions are in very close agreement with experiments and are consistent with other calculations.

Photoionization of Be, B+, C2+, N3+, O4+, and F5+ in the MCRRPA theory

The multiconfiguration relativistic random-phase approximation theory is applied to the valence-shell photoionization along the Be isoelectronic sequence. Photoionization cross sections between (1s22s)2S1/2 and (1s22p)2P°1/2 ionization thresholds are calculated. There are five Rydberg series of doubly excited states that manifest themselves as autoionization resonances in the photoionization cross section. A comparative study of Be, B+, C2+, N3+, O4+, and F5+ is presented.

Electron-impact ionization for U/sup 91+/ in the QED theory

Electron-impact ionization of highly charged ions is studied in the QED theory. Our calculation will include the transverse-photon interaction as well as the vacuum-polarization potential between charges. We apply the two-potential distorted wave approximation to compute the ionization cross sections. Both direct and exchange effects are considered. The calculated results are compared with those from other theories and with experiment.