Resonant Intermediate State Research Articles

Valence Electron Ionization Dynamics of Chromium by a Photoelectron Imaging Technique: J+-Dependent State and Angular Distribution

The photoionization of Cr at excited states is investigated using a velocity-map photoelectron imaging technique. Benzene chromium carbonyl or bis(η(6)-benzene) chromium was used as a precursor for the generation of excited Cr atoms. The a (5)S2 → x (5)P°3 and a (5)D3 → y (5)D°2 transitions are then employed for the preparation of resonant intermediate states in a two-color two-photon ionization process, in which an electronic configurational change from 3d(4)((5)D)4s4p((1)P°) to 3d(4)4s((6)D(J+)) occurs. The photoelectron kinetic energy distribution is found to be very sensitive to the ionization energy and the total angular momentum quantum number of the chromium ion (J(+)). Anisotropy parameters associated with departing electrons also show significant variation depending on the energy and total angular momentum quantum number, suggesting that direct and/or indirect ionization should be quantum-mechanically mixed, manifesting the complicated nature of angular momentum couplings in the ionization continuum.

Exponential and nonexponential buildup in resonant tunneling

The exponential and nonexponential regimes of the buildup process in resonant tunneling structures are analyzed by considering an analytic solution of the time-dependent Schr\"odinger equation. It is found that the buildup exhibits a purely exponential behavior in a finite time interval followed by a clear transition to a nonexponential regime. The buildup of the probability amplitude in the nonexponential regime follows a ${t}^{\ensuremath{-}3/2}$ time dependence, in the same fashion as the survival amplitude in quantum decay. For incidence energies at higher isolated resonances, $E={\ensuremath{\varepsilon}}_{n}$ with $n>1$, it is found that the exponential regime is split into two exponential subregimes: the first one is governed by the width ${\ensuremath{\Gamma}}_{n}$ of the resonance chosen for the incidence energy, and the second one is dominated by the width ${\ensuremath{\Gamma}}_{1}$ of the lowest resonance. The transition occurs directly from $n$ to 1 without jumps to other intermediate resonant states. This dynamics is discussed in comparison with the (opposite) and well-studied process of quantum decay, with which we find that there are striking similarities in both the exponential and nonexponential regimes. We also analyze the buildup in systems with resonance doublets, where the interference effects produced by the interacting resonances play an important role. In the latter case we find that the buildup of the probability amplitude exhibits a complex oscillatory behavior that can be characterized by a mix of oscillating contributions with well-defined Rabi type frequencies of the form $|E\ensuremath{-}{\ensuremath{\varepsilon}}_{n}|/\ensuremath{\hbar}$, where ${\ensuremath{\varepsilon}}_{n}$ are the nearest resonances around the incidence energy $E$.

Theory of X-Ray Anisotropy and Polarization Following the Dielectronic Recombination of Initially Hydrogen-Like Ions

The angular distribution and polarization of the x-ray photoemission of highly charged helium-like ions is studied following the K—LL dielectronic recombination of initially hydrogen-like ions. Calculation is carried out within the framework of the density matrix theory combined with the multiconfiguration Dirac—Fock approach. Attention is paid to magnetic sublevel alignment in the resonant intermediate state and to its nonuniform radiative decay processes. It is shown that the Breit interaction between the incident and target electrons plays a significant role for the alignment of the resonant state and thus causes a substantial change in the x-ray emission characteristic, when compared to the incorporation of only the (non-relativistic) Coulomb interaction. The most prominent difference in alignment parameter is found in the 2s2p1/2 J = 1 resonant state for a wide range of atomic numbers from 9 to 92. For this resonant state of helium-like ions, the Breit interaction becomes significant for ions with nuclear charge Z ∼ 30 already.

Ξ− hyperon and hypernuclear production in the (K−,K+) reaction on nucleon and nuclei in a field theoretical model

We investigate the production of a cascade hyperon ($\Xi$) and bound $\Xi^-$ hypernuclei in the $(K^-,K^+)$ reaction on proton and nuclear targets, respectively, within a covariant effective Lagrangian model. The $K^+\Xi^-$ production vertex is described by excitation, propagation and decay of $\Lambda$ and $\Sigma$ resonance states in the initial collision of a $K^-$ meson with a free or bound proton in the incident channel. The parameters of the resonance vertices are taken from previous studies and SU(3) symmetry considerations. The model is able to provide a good description of the available data on total and differential cross sections for the $p(K^-, K^+)\Xi^-$ reaction. The same mechanism was used to describe the hypernuclear production reactions $^{12}$C$(K^-,K^+)^{12}{/!/!/!_{/Xi^-}}$Be and $^{28}$Si$(K^-,K^+)^{28}{/!/!/!_{\Xi^-}}$Mg, where $\Xi$ bound state spinors calculated within a phenomenological model have been employed. Both the elementary and hypernuclear production cross sections are dominated by the contributions from the $\Lambda$(1520) intermediate resonant state. The beam momentum dependence of the $0^\circ$ differential cross sections for the formation of the $\Xi$ hypernuclei is found to be remarkably different from what has been observed previously in the impulse approximation model calculations

Orientation dependence of nonadiabatic molecular high-order-harmonic generation from resonant polar molecules

Orientation-dependent nonadiabatic molecular high-order-harmonic generation (MHOHG) is studied for the one-electron polar diatomic molecular ion HeH${}^{2+}$ exposed to short, linearly polarized, intense laser fields. The fully dimensional time-dependent Schr\"odinger equation is solved numerically. The resonance of excited states is maximal in the parallel orientation, while it is minimal in the perpendicular case for the nonsymmetric molecular ion. The resulting redshift and the overall intensity of MHOHG strongly depend on the electronic symmetry and charge transfer of the resonant excited states. These results are used to confirm the proposed four-step model in MHOHG involving intermediate resonance states.

Multiplet resonance lifetimes in resonant inelastic x-ray scattering involving shallow core levels

Resonant inelastic x-ray scattering (RIXS) spectra of model copper- and nickel-based transition metal oxides are measured over a wide range of energies near the M edge ($h\ensuremath{\nu}=60$--80 eV) to better understand the properties of resonant scattering involving shallow core levels. Standard multiplet RIXS calculations are found to deviate significantly from the observed spectra. However, by incorporating the self-consistently calculated decay lifetime for each intermediate resonance state within a given resonance edge, we obtain dramatically improved agreement between data and theory. Our results suggest that these textured lifetime corrections can enable a quantitative correspondence between first-principles predictions and RIXS data on model multiplet systems. This accurate model is also used to analyze resonant elastic scattering, which displays the elastic Fano effect and provides a rough upper bound for the core hole shakeup response time.

Detection of Atmospheric Pollutant NO With the Method of Resonant-Enhanced Multiphoton Ionization

NO is one of the key substances of air pollution. This paper presents the use of the technique of resonant enhanced multi-photon ionization (REMPI) for NO ambient detection. NO is ionized by absorbing four photons and via A2Σ intermediate resonant state when use 452.4nm laser as radiation source. A physical model concerning the ionization process is presented. It is shown that the ion signal depends on laser character and the dynamic parameters of NO. Two-photon absorption and ionization cross section about the resonant state are obtained from the ion decay curve and the model. The detection limit of this work, which can reach 1.4 ppm, is determined by measuring the variation of the ion signal with the concentration of NO.

Measurement of the argon-gas-induced broadening and line shifting of the barium Rydberg level 6s24d 1D2 by two-photon resonant nondegenerate four-wave mixing

We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state to the observation of the broadening and shifting of the barium Rydberg level 6s24d 1D2 by collision with argon. The collision broadening and shifting cross sections are measured. This technique is purely optical, and can investigate the pressure dependence of the transverse relaxation rate Γ21 between the Rydberg state and an intermediate state, as well as the transverse relaxation rate Γ20 between the Rydberg state and the ground state.

Amplitude analysis and measurement of the time-dependentCPasymmetry ofB0→KS0KS0KS0decays

We present the first results on the Dalitz-plot structure and improved measurements of the time-dependent CP-violation parameters of the process B0→KS0KS0KS0 obtained using 468×106 BB¯ decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. The Dalitz-plot structure is probed by a time-integrated amplitude analysis that does not distinguish between B0and B¯0 decays. We measure the total inclusive branching fraction B(B0→KS0KS0KS0)=(6.19±0.48±0.15±0.12)×10−6, where the first uncertainty is statistical, the second is systematic, and the third represents the Dalitz-plot signal model dependence. We also observe evidence for the intermediate resonant states f0(980), f0(1710), and f2(2010). Their respective product branching fractions are measured to be (2.70−1.19+1.25±0.36±1.17)×10−6, (0.50−0.24+0.46±0.04±0.10)×10−6, and (0.54−0.20+0.21±0.03±0.52)×10−6. Additionally, we determine the mixing-induced CP-violation parameters to be S=−0.94−0.21+0.24±0.06 and C=−0.17±0.18±0.04, where the first uncertainty is statistical and the second is systematic. These values are in agreement with the standard model expectation. For the first time, we report evidence of CP violation in B0→KS0KS0KS0 decays; CP conservation is excluded at 3.8 standard deviations including systematic uncertainties.3 MoreReceived 16 November 2011DOI:https://doi.org/10.1103/PhysRevD.85.054023© 2012 American Physical Society

Production of cascade hypernuclei via the () reaction within a quark–meson coupling model

We study the production of bound cascade hypernuclei via the (K-,K+) reaction on 12C and 28Si targets within a covariant effective Lagrangian model, employing the cascade bound state spinors derived from the latest quark-meson coupling model as well as Dirac single particle wave functions. The K+-cascade production vertex is described by excitation, propagation and decay of Lambda and Sigma resonance states in the initial collision of a K- meson with a target proton in the incident channel. The parameters of the resonance vertices are fixed by describing the available data on total and differential cross sections for the cascade production in elementary (K-,K+) reaction. We find that both the elementary and hypernuclear production cross sections are dominated by the contributions from the Lambda(1520) intermediate resonant state. The 0 degree differential cross sections for the formation of simple s-state cascade particle-hole states peak at a beam momentum around 1.0 GeV/c, with a value in excess of 1 mub.

Measurement of the argon-gas-induced broadening and shifting of the barium Rydberg levels by two-photon resonant nondegenerate four-wave mixing

We apply two-photon resonant nondegenerate four-wave mixing with a resonant intermediate state for observing the broadening and the shifting of the barium Rydberg 6snd 1D2 series by collision with argon. The collision broadenings and the collision shifting cross sections are measured for n=1633. This technique is a purely optical means, and can achieve Doppler-free resolution of narrow spectral structures of Rydberg levels when the incident lasers have narrow bandwidths. Different from other experimental methods of studying the pressure dependence of the longitudinal relaxation rate of Rydberg states, our method is to investigate the pressure dependence of the transverse relaxation rate of the transition.

Production of a cascade hyperon in theK−-proton interaction

We investigate the production of a cascade hyperon (Xi) through the K^- + p --> K^+ (K^0) + Xi^- (Xi^0) reactions, within an effective Lagrangian model where these reactions proceed via excitations of Lambda and Sigma resonance intermediate states in s- and u-channels. The coupling constants at the various vertices are taken from previous studies and SU(3) symmetry considerations. The calculated total cross sections of these reactions, which are in good agreement with the available data, are dominated by the contributions from the Lambda(1520) intermediate resonant state. However, the K^+ meson angular distributions show selectivity to other resonant states in different angular regions and interference among these states leads to their strong backward peaking.

The other Higgses, at resonance, in the Lee-Wick extension of the Standard Model

Within the framework of the Lee-Wick Standard Model (LWSM) we investigate Higgs pair production gg → h 0 h 0, $ gg \to {h_0}{\tilde{p}_0} $ and top pair production $ gg \to \bar{t}t $ at the Large Hadron Collider (LHC), where the neutral particles from the Higgs sector (h 0, $ {\tilde{h}_0} $ and $ {\tilde{p}_0} $ ) appear as possible resonant intermediate states. Depending on whether the LW Higgs state is below or above the top pair threshold either the hh or tt-channel are dominant and therefore of main interest. We investigate the signal $ gg \to {h_0}{h_0} \to \bar{b}b\gamma \gamma $ and we find that the LW Higgs, depending on its mass-range, can be seen not long after the LHC upgrade in 2012. In $ gg \to \bar{t}t $ the LW states, due to the wrong-sign propagator and negative width, lead to a dip-peak structure instead of the usual peak-dip structure which gives a characteristic signal especially for low-lying LW Higgs states. We comment on the LWSM and the forward-backward asymmetry in view of the measurement at the TeVatron. Furthermore, we present a technique which reduces the hyperbolic diagonalization to standard diagonalization methods. We clarify issues of spurious phases in the Yukawa sector.

Multiphoton ionization of H2+in xuv laser pulses

We consider the ionization of the hydrogen molecular ion after one-, two-, and three-photon absorption over a large range of photon energies between 9 and 40 eV in the fixed-nuclei approximation. The temporal development of the system is obtained in a fully ab initio time-dependent grid-based approach in prolate spheroidal coordinates. The alignment dependence of the one-photon ionization amplitude is highlighted in the framework of time-dependent perturbation theory. For one-photon ionization as a function of the nuclear separation, the calculations reveal a significant minimum in the ionization probability. The suppressed ionization is attributed to a Cooper-type minimum, which is similar, but not identical, to the cancellation effect observed in photoionization cross sections of some noble-gas atoms. The effect of the nonspherical two-center Coulomb potential is analyzed. For two- and three-photon ionization, the angle-integrated cross sections clearly map out intermediate-state resonances, and the predictions of the current computations agree very well with those from time-independent calculations. The dominant emission modes for two-photon ionization are found to be very similar in both resonance and off-resonance regions.

Cross sections for 14-eVe-H2resonant collisions: Isotope effect in dissociative electron attachment

The process of dissociative attachment of electrons to molecular hydrogen and its isotopes in the energy range at approximately 14 eV is investigated. The dissociative electron attachment cross sections for all six hydrogen isotopes are calculated over an extended range of electron energies using the local complex potential model with the excited Rydberg {sup 2}{Sigma}{sub g}{sup +} electronic state of H{sub 2}{sup -} acting as the intermediate resonant state. A significant isotope effect in theoretical electron attachment cross sections is observed, in agreement with previous predictions and experimental observations. A two-parameter analytic expression for the cross section is derived from the theory that fits accurately the numerically calculated cross sections for all isotopes. Similarly, an analytic mass-scaling relation is derived from the theory that accurately reproduces the numerically calculated rate coefficients for all isotopes in the 0.1-1000 eV temperature range by using the rate coefficient for the H{sub 2} isotope only. The latter is represented by an analytic fit expression with two parameters only.

Damped response theory description of two-photon absorption

Damped response theory is applied to the calculation of two-photon absorption (TPA) spectra, which are determined directly, at each frequency, from a modified damped cubic response function. The TPA spectrum may therefore be evaluated for selected frequency ranges, making the damped TPA approach attractive for calculations on large molecules with a high density of states, where the calculation of TPA using standard theory is more problematic. Damped response theory can also be applied to the case of intermediate state resonances, where the standard TPA expression is divergent. Both exact damped response theory and its application within density functional theory are discussed. The latter is implemented using an atomic-orbital based density matrix formulation, which makes the approach especially suitable for studies on large systems. A test preliminary study is presented for the TPA spectrum of R-(+)-1,1'-bi(2-naphtol).

Two-photon-induced x-ray emission in neon atoms

We investigated the resonant x-ray emission from a neon atom induced by the two-photon population of a double-core-hole excited state. Two qualitatively different schemes of this process are studied: The first one involves an off-resonant intermediate single-core-hole state; the second scheme passes through a resonant core-ionized intermediate state. The numerical simulations of the resonant x-ray emission performed for different peak intensities and pulse durations show significant population of the double-core-hole final states. Therefore, rather strong two-photon absorption-induced x-ray emission is predicted for both studied schemes. Thus, high counting rates in experimental measurements are expected.

Λ(1520)photoproduction off a proton target with Regge contributions

We investigate the $\ensuremath{\Lambda}(1520,3/{2}^{\ensuremath{-}})\ensuremath{\equiv}{\ensuremath{\Lambda}}^{*}$ photoproduction off the proton target beyond the resonance region within a model including the Regge contributions, the tree-level diagrams with the nucleon and the certain resonance intermediate states, and one contact term. The Reggeized propagators for the $K$ and ${K}^{*}$ exchanges in the $t$ channel are employed in a gauge-invariant manner. We compute the angular and energy dependences of the cross section and some polarization observables, such as the photon-beam asymmetry and the polarization-transfer coefficients. Our results qualitatively agree with the current experimental data. We find that the Regge contributions are necessary to explain the high-energy data beyond ${E}_{\ensuremath{\gamma}}\ensuremath{\approx}4$ GeV, especially for the angular dependences in the forward region. On the contrary, the polarization observables are insensitive to the Regge contributions due to the contact-term dominance, which is a consequence of gauge invariance. We also calculate the ${K}^{\ensuremath{-}}$-angle distribution function in the Gottfried-Jackson frame, using the polarization-transfer coefficients in the $z$ direction. We find that it owns a complicated angle and energy dependences in the forward ${K}^{+}$ scattering region.

Two-boson exchange corrections to parity-violating elastic electron-proton scattering

Details of the calculation of two-boson exchange effects in parity-violating elastic $\mathit{ep}$ scattering within a simple hadronic model, including both the nucleon and the $\ensuremath{\Delta}(1232)$-resonance intermediate states, are presented. We examine the sensitivity of our results with respect to choice of form factors. We emphasize the importance of using correct relations relating $N\ensuremath{\rightarrow}\ensuremath{\Delta}$ and $\ensuremath{\Delta}\ensuremath{\rightarrow}N$ transition vertex functions. The $N\ensuremath{\Delta}$ Coulomb quadrupole transition is found to play an important role at higher ${Q}^{2}\ensuremath{\geqslant}3.0$ GeV${}^{2}$. We also elucidate the relation between our results and the well-known result on the $\ensuremath{\gamma}Z$-boson exchange effect given by Marciano and Sirlin. The effect of the nucleon contribution ${\ensuremath{\delta}}_{N}$ to parity asymmetry ${A}_{\mathrm{PV}}$ is found to be, in general, larger than the corresponding $\ensuremath{\Delta}$ contribution ${\ensuremath{\delta}}_{\ensuremath{\Delta}}$ except at extreme forward angles. Corrections to the extracted values of the strange form factors ${G}_{E}^{s}+\ensuremath{\beta}{G}_{M}^{s}$ from the HAPPEX, A4, and G0 data are also presented. The total TBE corrections to the extracted values of ${G}_{E}^{s}+\ensuremath{\beta}{G}_{M}^{s}$ in recent HAPPEX, G0, and A4 experiments are, depending on kinematics, found to be small except in a few cases where they range from $\ensuremath{-}20.6%$ to $48.3%$.

A relativistic description of the [formula omitted] reaction

We investigate the A ( π + , K + ) Λ A reaction within a covariant model. We consider those amplitudes which are described by creation, propagation and decay into the relevant channel of N ∗ (1650), N ∗ (1710), and N ∗ (1720) intermediate baryonic resonance states in the initial collision of the incoming pion with one of the target nucleons. The bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. Expressions for the reaction amplitudes are derived taking continuum particle wave function in the plane wave approximation. Numerical calculations are presented for reactions on 12C, 40Ca, 51V and 89Y target nuclei. The predictions of our model are in reasonable agreement with the available experimental data.