Radiative Widths Research Articles

Photon and vector meson exchanges in the production of light meson pairs and elementary atoms

The production of pseudoscalar and scalar meson pairs ππ, ηη, η′η′, σσ as well as bound states in high energy γγ collisions are considered. The exchange by a vector particle in the binary process γ + γ → ha + hb with hadronic states ha, hb in fragmentation regions of the initial particle leads to nondecreasing cross sections with increasing energy, that is a priority of peripheral kinematics. Unlike the photon exchange the vector meson exchange needs a reggeization leading to fall with energy growth. Nevertheless, due to the peripheral kinematics beyond very forward production angles the vector meson exchanges dominate over all possible exchanges. The proposed approach allows one to express the matrix elements of the considered processes through impacting factors, which can be calculated in perturbation models like chiral perturbation theory (ChPT) or the Nambu–Jona–Lasinio (NJL) model. In particular cases the impact factors can be determined from relevant γγ sub-processes or the vector meson radiative decay width. The pionium atom production in the collisions of high energy electrons and pions with protons is considered and the relevant cross sections have been estimated.

ANALYSIS OF THE RADIATIVE DECAYS AMONG THE BOTTOMONIUM STATES

In this paper, we perform an systematic study of the radiative transitions among the bottomonium states using the heavy quarkonium effective Lagrangians, and make predictions for the ratios among the radiative decay widths of a special multiplet to another multiplet. The predictions can be confronted with the experimental data in the future.

From average parameters to statistical resolved resonances

This paper presents a novel approach using average parameters from statistical models in the continuum to produce statistical resolved resonances in the resonance range. Based on unresolved resonance parameters and the random ladder method, average parameters such as the scattering radius, level spacing, reduced neutron width and the radiative width are used to create resolved resonances from thermal energy up to the first excited level. Using the TALYS reaction code and the CALENDF processing code, the method is tested on ≃2400 isotopes and will be used to produce resolved resonance ranges in the TENDL libraries for reactions missing experimental resolved and unresolved parameters. Additionally, the R-matrix code AVEFIT is used to approximate the resonance structure effects above the first excited level of selected isotopes.

Angular distribution of Cherenkov radiation from relativistic heavy ions taking into account deceleration in the radiator

Numerical methods are used to study the dependence of the structure and the width of the angular distribution of Vavilov-Cherenkov radiation with a fixed wavelength in the vicinity of the Cherenkov cone on the radiator parameters (thickness and refractive index), as well as on the parameters of the relativistic heavy ion beam (charge and initial energy). The deceleration of relativistic heavy ions in the radiator, which decreases the velocity of ions, modifies the condition of structural interference of the waves emitted from various segments of the trajectory; as a result, a complex distribution of Vavilov-Cherenkov radiation appears. The main quantity is the stopping power of a thin layer of the radiator (average loss of the ion energy), which is calculated by the Bethe-Bloch formula and using the SRIM code package. A simple formula is obtained to estimate the angular distribution width of Cherenkov radiation (with a fixed wavelength) from relativistic heavy ions taking into account the deceleration in the radiator. The measurement of this width can provide direct information on the charge of the ion that passes through the radiator, which extends the potentialities of Cherenkov detectors. The isotopic effect (dependence of the angular distribution of Vavilov-Cherenkov radiation on the ion mass) is also considered.

Chaos-induced enhancement of resonant multielectron recombination in highly charged ions: Statistical theory

A statistical theory of resonant multielectron recombination based on properties of chaotic eigenstates is developed. The level density of many-body states increases exponentially with the number of excited electrons. When the residual electron-electron interaction exceeds the interval between these levels, the eigenstates (called compound states or compound resonances if these states are in the continuum) become ``chaotic'' superpositions of large numbers of Hartree-Fock configurational basis states. This situation takes place in some rare-earth atoms and many open-shell multiply charged ions excited in the process of electron recombination. Our theory describes resonant multielectron recombination via dielectronic doorway states leading to such compound resonances. The result is a radiative capture cross section averaged over a small energy interval containing several compound resonances. In many cases individual resonances are not resolved experimentally (since the interval between them is small, e.g., $\ensuremath{\le}$1 meV, possibly even smaller than their radiative widths); therefore, our statistical theory should correctly describe the experimental data. We perform numerical calculations of the recombination cross sections for tungsten ions W${}^{q+}$, $q=18$--25. The recombination rate for W${}^{20+}$ measured recently [Schippers et al. Phys. Rev. A 83, 012711 (2011)] is ${10}^{3}$ greater than the direct radiative recombination rate at low energies, and our result for W${}^{20+}$ agrees with the measurements.

Neutron resonance data exclude random matrix theory

AbstractAlmost since the time it was formulated, the overwhelming consensus has been that random matrix theory (RMT) is in excellent agreement with neutron resonance data. However, over the past few years, we have obtained new neutron‐width data at Oak Ridge and Los Alamos National Laboratories that are in stark disagreement with this theory. We also have reanalyzed neutron widths in the most famous data set, the nuclear data ensemble (NDE), and found that it is seriously flawed, and, when analyzed carefully, excludes RMT with high confidence. More recently, we carefully examined energy spacings for these same resonances in the NDE using the Δ3 statistic. We conclude that the data can be found to either confirm or refute the theory depending on which nuclides and whether known or suspected p‐wave resonances are included in the analysis, in essence confirming results of our neutron‐width analysis of the NDE. We also have examined radiation widths resulting from our Oak Ridge and Los Alamos measurements, and find that in some cases they do not agree with RMT. Although these disagreements presently are not understood, they could have broad impact on basic and applied nuclear physics, from nuclear astrophysics to nuclear criticality safety.

Atomic decay data for modeling K lines of iron peak and light odd-Zelements

Complete data sets of level energies, transition wavelengths, A-values, radiative and Auger widths and fluorescence yields for K-vacancy levels of the F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu and Zn isonuclear sequences have been computed by a Hartree-Fock method that includes relativistic corrections as implemented in Cowan's atomic structure computer suite. The atomic parameters for more than 3 million fine-structure K lines have been determined. Ions with electron number N greater than 9 are treated for the first time, and detailed comparisons with available measurements and theoretical data for ions with N less than or equal to 9 are carried out in order to estimate reliable accuracy ratings.

Calculation of the heavy-hadron axial couplingsg1,g2, andg3using lattice QCD

In a recent letter [Phys. Rev. Lett. 108, 172003 (2012)] we have reported on a lattice QCD calculation of the heavy-hadron axial couplings ${g}_{1}$, ${g}_{2}$, and ${g}_{3}$. These quantities are low-energy constants of heavy-hadron chiral perturbation theory ($\mathrm{HH}\ensuremath{\chi}\mathrm{PT}$) and are related to the ${B}^{*}B\ensuremath{\pi}$, ${\ensuremath{\Sigma}}_{b}^{*}{\ensuremath{\Sigma}}_{b}\ensuremath{\pi}$, and ${\ensuremath{\Sigma}}_{b}^{(*)}{\ensuremath{\Lambda}}_{b}\ensuremath{\pi}$ couplings. In the following, we discuss important details of the calculation and give further results. To determine the axial couplings, we explicitly match the matrix elements of the axial current in QCD with the corresponding matrix elements in $\mathrm{HH}\ensuremath{\chi}\mathrm{PT}$. We construct the ratios of correlation functions used to calculate the matrix elements in lattice QCD, and study the contributions from excited states. We present the complete numerical results and discuss the data analysis in depth. In particular, we demonstrate the convergence of $SU(4|2)$ $\mathrm{HH}\ensuremath{\chi}\mathrm{PT}$ for the axial-current matrix elements at pion masses up to about 400 MeV and show the impact of the nonanalytic loop contributions. Finally, we present additional predictions for strong and radiative decay widths of charm and bottom baryons.

Ultrafast absorption of intense x rays by nitrogen molecules

We devise a theoretical description for the response of nitrogen molecules (N(2)) to ultrashort and intense x rays from the free electron laser Linac Coherent Light Source (LCLS). We set out from a rate-equation description for the x-ray absorption by a nitrogen atom. The equations are formulated using all one-x-ray-photon absorption cross sections and the Auger and radiative decay widths of multiply-ionized nitrogen atoms. Cross sections are obtained with a one-electron theory and decay widths are determined from ab initio computations using the Dirac-Hartree-Slater (DHS) method. We also calculate all binding and transition energies of nitrogen atoms in all charge states with the DHS method as the difference of two self-consistent field (SCF) calculations (ΔSCF method). To describe the interaction with N(2), a detailed investigation of intense x-ray-induced ionization and molecular fragmentation are carried out. As a figure of merit, we calculate ion yields and the average charge state measured in recent experiments at the LCLS. We use a series of phenomenological models of increasing sophistication to unravel the mechanisms of the interaction of x rays with N(2): a single atom, a symmetric-sharing model, and a fragmentation-matrix model are developed. The role of the formation and decay of single and double core holes, the metastable states of N(2)(2+), and molecular fragmentation are explained.

A compact collinear polarization gating scheme for many cycle laser pulses

We demonstrate the generation of a broadband coherent continuum extreme-ultraviolet (XUV) radiation produced by the interaction of gases with a many-cycle infrared (IR) laser field, utilizing a compact collinear many cycle-polarization gating (CMC-PG) device. The spectral width of the XUV radiation can support isolated pulses of 200 asec duration. The CMC-PG device forms a high energy content ultra-short temporal gate in a many-cycle laser pulse, within which the XUV emission is taking place. The gate width has been measured and is in agreement with the theoretical calculations. The simplicity, the compactness, the long term stability, and the high IR energy output within the gate, make the CMC-PG device an ideal tool for generating energetic isolated attosecond pulses and measure the carrier-envelope phase of a high-power many-cycle laser field.

Room temperature superradiance due to coherent coupling between light and extended single quantum state

We have established the newly-developed growth method of high-quality CuCl thin film based on molecular-beam epitaxy. In qualified films, where harmonized coupling between an excitonic polarization wave and a resonant electromagnetic wave over a range of multiple wavelengths is achieved, we have observed an exceptionally high speed nonlinear response of excitons at room temperature, wherein the excitons decay radiatively before its coherence is destroyed by dephasing. A component with extremely large radiative width can be observed in the nonlinear optical spectrum only when the other components with smaller radiative widths disappear by the room-temperature dephasing. The radiative decay time of the excitonic state with the largest radiative width reaches the order of 100fs, which is much faster than the dephasing process. The mechanism demonstrated by our results contradicts the conventional physical description of light–matter interaction based on the long-wavelength approximation. The shapes of the measured degenerate four-wave mixing spectrum and the radiative decay profile closely reflect those of the calculated induced-polarization spectrum and the radiative decay profile obtained by real-time analysis, respectively.

Electromagnetic transition properties of Δ → Nγ in a hypercentral scheme

The electromagnetic transition properties of the decuplet to octet baryon (Δ → Nγ) is studied within the framework of a hypercentral quark model. The confinement potential is assumed as a hypercentral coloumb plus linear potential. The transition magnetic moment and transition amplitude fM1 for the Δ → Nγ are in agreement with other theoretical predictions. The present result of the radiative decay width is found to be in excellent agreement with the experimental values reported by the particle data group over other theoretical model predictions.

Radiative transitions from Rydberg states of lithium atoms in a blackbody radiation environment

The radiative widths induced by blackbody radiation (BBR) were investigated for Rydberg states with principal quantum number up to n = 1000 in S-, P- and D-series of the neutral lithium atom at temperatures T = 100–3000 K. The rates of BBR-induced decays and excitations were compared with the rates of spontaneous decays. Simple analytical approximations are proposed for accurate estimations of the ratio of thermally induced decay (excitation) rates to spontaneous decay rates in wide ranges of states and temperatures.

VECTOR MESON DOMINANCE AND RADIATIVE DECAYS OF HEAVY SPIN-3/2 BARYONS TO HEAVY SPIN-1/2 BARYONS

Using the calculated values of the strong coupling constants of the heavy sextet spin-3/2 baryons to sextet and antitriplet heavy spin-1/2 baryons with light vector mesons within the light cone QCD sum rules method, and vector meson dominance assumption, the radiative decay widths are calculated. These widths are compared with the "direct" radiative decay widths predicted in the framework of the light cone QCD sum rules.

Abrupt Change in Radiation-Width Distribution forSm147Neutron Resonances

We obtained the total radiation widths of s-wave resonances through an R-matrix analysis of (147)Sm(n,γ) cross sections. Distributions of these widths differ markedly for resonances below and above E(n)=300 eV, which is in stark contrast to long-established theory. We show that this change, as well as a similar change in the neutron-width distribution reported previously, is reflected in abrupt increases in both the average (147)Sm(n,γ) cross section and fluctuations about the average near 300 eV. Such effects could have important consequences for applications such as nuclear astrophysics and nuclear criticality safety.

Fluorescence and Auger Decay Properties of the Core-Excited F-Like Ions from Ne to Kr

We systematically study the decay properties of the K-shell excited F-like ions with 10≤Z≤36 based on the multiconfiguration Dirac—Fock method. The Breit interaction, the QED corrections and the nuclear finite mass effects are also considered as perturbation. Auger transition rates, radiative, Auger and natural widths, as well as fluorescence and Auger yields for K-shell excited F-like ions are presented. It is shown by means of concrete figures that the decay properties change significantly with the increase of the atomic number Z; the Auger rate is overtaken at Z = 30 by the radiative decay rate. Several fitting formulae for the radiative and Auger widths and the fluorescence yields have been evaluated which is expected to be useful in plasma analysis and plasma modeling.

Vector and Tensor Coupling Constants of SU(3) Baryons in a Chiral Soliton Model

We report in the present talk a recent investigation on the vector properties of SU(3) baryons, based on a chiral soliton model. All relevant parameters from the model are adjusted to the experimental data of the masses and magnetic moments of the baryon octet. We compute the electromagnetic transitions for the baryon octet, the decuplet, and the antidecuplet. The numerical predictions for transition magnetic moments and radiative partial decay widths are in a very good agreement with all data of existing experiment and the vector meson dominance being used, the coupling constants for the vector mesons and antidecuplet baryon vertices are determined from the calculated transition magnetic moments.

Direct two-XUV-photon double ionization in xenon

We report the observation of the direct two-XUV-photon double ionization of xenon by energetic coherent XUV continuum radiation. The spectrum of the XUV continuum spans from ∼15 to ∼23 eV, for which the two-photon sequential double ionization channel is partially open. The two-XUV-photon process is exploited in a second-order autocorrelation measurement of the temporal width of the continuum radiation, revealing energetic XUV pulses at the border between the atto- and femto-second scales.

Extrapolation of astrophysical S factors for the reaction 14N((p, γ) 15O to near-zero energies

The astrophysical S factors for the radiative-capture reaction 14N(p, γ)15O in the region of ultralow energies were calculated on the basis of the R-matrix approach. The values of the radiative and protonic widths were fitted to new experimental data. The contribution of direct radiative capture to bound states of the 15O nucleus was determined with the aid of asymptotic normalization coefficients, whose values were refined in the present study on the basis of the results obtained from an analysis of the reaction 14N(3He, d)15O at three different energies of incident helium ions. A value of S(0) = 1.79 ± 0.31 keV b was obtained for the total astrophysical S factor, and the reaction rate was determined for the process 14N(p, γ)15O.

Neutron resonance parameters in155Gd measured with the DANCEγ-ray calorimeter array

The ${}^{155}$Gd($n$,$\ensuremath{\gamma}$) reaction was measured with the DANCE $\ensuremath{\gamma}$-ray calorimeter at the Los Alamos Neutron Science Center. Spins were determined for the $s$-wave resonances by analysis of the $\ensuremath{\gamma}$-ray multiplicity distributions. The analysis was performed with a pattern recognition method. The resulting level densities for the $J=1$ and 2 resonances are in qualitative agreement with the expected 2$J$ $+$ 1 dependence. The average $s$-wave resonance spacing was determined to be ${D}_{0}=1.62$ $\ifmmode\pm\else\textpm\fi{}$ 0.15 eV. Analysis of the neutron resonances with the code sammy yielded the $s$-wave strength function ${S}_{0}=1.99\ifmmode\pm\else\textpm\fi{}0.28\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and the average total radiative width ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$ $=$ 120 $\ifmmode\pm\else\textpm\fi{}$ 3 meV.