Searcharxiv⌕ Search

arXiv subjects

D. H. Jakubassa-Amundsen

Publications and source records attributed to D. H. Jakubassa-Amundsen.

18 recordsLinked to original sources
arXiv2026

Radiative corrections to the parity-violating spin asymmetry

The parity-violating spin asymmetry Apv for elastic electron scattering from spin-zero nuclei, together with its QED corrections, is evaluated non-perturbatively within the phase-shift analysis. Dispersion corrections, taking into account low-lying transient nuclear excitations, are estimated with the help of the lowest-order $γZ$ box diagrams. Collision energies between 5 $-$ 500 MeV are considered, and results are provided for the $^{12}$C and $^{208}$Pb target nuclei. In addition, we have evaluated Apv at GeV energies and small scattering angles -- relevant for the Pb Radius Experiment (PREx) -- revealing that the low-lying nuclear excited states give no measurable dispersive contribution. However, they are important at lower energies and backward angles.

nucl-th↗
arXiv2026

The parity-violating asymmetry including QED corrections in high-energy electron-nucleus collisions

The parity-violating asymmetry, accounting for the vector and axial-vector vertex plus self-energy correction as well as for vacuum polarization, is calculated nonperturbatively by solving the corresponding Dirac equation for the electronic scattering states. Investigating the nuclei $^{27}$Al, $^{48}$Ca and $^{208}$Pb at collision energies in the GeV region and at forward scattering angles matching the experimental geometries, it is found that the combined QED effects change the parity-violating asymmetry by less than one percent. The same is true for $^{12}$C and $^{208}$Pb at an energy of 150 MeV.

nucl-th↗
arXiv2026

Radiative corrections to elastic electron-carbon scattering cross sections in comparison with experiment

The influence of dispersion on the differential scattering cross section in the vicinity of the first diffraction minimum is revisited for collision energies between 200 and 450 MeV. Transient nuclear excitations in the giant resonance region with angular momentum L \leq 3 are taken into consideration within updated numerics. Moreover, the deviations of the nonperturbative QED corrections from the conventionally used smooth Born predictions are accounted for. A qualitative agreement with the measurements is only obtained for the lowest energy, while dispersion within the present model is too small at the higher energies.

nucl-th↗
arXiv2025

Radiative corrections to the spin asymmetry in elastic polarized electron-nucleus collisions at high energy

Modifying the numerical codes, dispersion corrections to the beam-normal spin asymmetry which arise from low-lying transient nuclear excitations up to 30 MeV, are estimated for collision energies between 50 MeV and 1 GeV. A nonperturbative calculation of vacuum polarization and the vertex plus self-energy correction, using optimized potentials, indicates that for small scattering angles both these quantum electrodynamical (QED) effects on the spin asymmetry decrease with energy above 200 MeV and can be neglected at high energies. Examples are given for the 12C and 208Pb nuclei. The available measurements of the spin asymmetry at collision energies beyond 500 MeV cannot be explained by the present theory.

nucl-th↗
arXiv2025

Dispersion effects in elastic electron scattering from $^{208}$Pb

Dispersion corrections to elastic electron scattering from $^{208}$Pb at energies up to 150 MeV are estimated within the second-order Born approximation. All strong transient nuclear excited states with angular momentum up to $L=3$ and natural parity are taken into consideration. It is found that at small scattering angles the high-lying $L=1$ isovector states provide the dominant contribution to the dispersive change of the differential cross section and of the beam-normal spin asymmetry. At the backmost angles these changes are considerably smaller and are basically due to the isoscalar $L=2$ and, to a lesser extent, $L=3$ states. In comparison with the findings for $^{12}$C, the dispersive cross-section modifications for $^{208}$Pb are significantly larger, while the spin-asymmetry changes are much smaller at all angles. The latter originates from the destructive interference of the multipole contributions in $^{208}$Pb that switch sign when proceeding from $L$ to $L+1$. This mechanism might be the origin of the small beam-normal spin asymmetries recently measured in ${}^{208}$Pb at much larger energies.

nucl-th↗
arXiv2025

The Electron-Gamma Coincidence Setup DAGOBERT

The QCLAM electron spectrometer at the S-DALINAC electron accelerator at Technische Universität Darmstadt has been extended by the DAGOBERT $γ$-detector array consisting of fast timing and high efficiency LaBr$_3$:Ce detectors to perform electron-gamma coincidence measurements. The functionality of the setup and data acquisition system was demonstrated in a commissioning measurement on $^{12}\textrm{C}$ observing the $4.44\,$MeV and $15.11\,$MeV states. A medium-heavy nucleus, $^{96}\textrm{Ru}$, has been studied for the first time up to excitation energies of $15\,$MeV using the $(e,e'γ)$ reaction. In particular, the angular distribution of the $2_1^+$ state and the $γ$-decay branching ratios of the mixed-symmetric $2_3^+$ state were observed. DAGOBERT@QCLAM is a new and worldwide unique setup for nuclear structure studies of excitation and decay using purely electromagnetic probes, with a significantly improved sensitivity compared to previous experiments.

physics.ins-det↗
arXiv2024

Electron-nucleus scattering and the polarization sum rules

A formal derivation of the polarization correlations between the incident electron and the scattered electron is given for a general class of transition operators. In correspondence to the case of bremsstrahlung emission, three sum rules for the polarization correlations are predicted, which reduce to the known one for potential scattering. Further examples, including the 1_2^+ and 2_1^+ excitations of the 12C nucleus and a 1^- excitation of the 208Pb nucleus, are discussed and the validity of the corresponding sum rules is investigated.

nucl-th↗
arXiv2023

QED corrections to elastic electron-nucleus scattering beyond the first-order Born approximation

A potential for the vertex and self-energy correction is derived from the first-order Born theory. The inclusion of this potential in the Dirac equation, together with the Uehling potential for vacuum polarization, allows for a nonperturbative treatment of these QED effects within the phase-shift analysis. Investigating the 12C and 208Pb targets, a considerable deviation of the respective cross-section change from the Born results is found, which becomes larger with increasing momentum transfer. Estimates for the correction to the beam-normal spin asymmetry are also provided. For the 12C nucleus, dispersion effects are considered as well.

nucl-th↗
arXiv2021

On the QED corrections to elastic electron scattering at high momentum transfer

Estimates of QED and dispersion effects on the cross section for elastic electron scattering from a 12C nucleus are provided for collision energies in the range of 120-450 MeV. While in general such corrections are smoothly varying with energy or scattering angle, they show structures in the vicinity of diffraction minima which are very sensitive to details of the theoretical models. This casts doubt on the assertion that the discrepancy between QED background-corrected experimental data and theory in these minima originates solely from dispersion.

nucl-th↗
arXiv2021

Numerical test of polarization sum rules for the triply differential bremsstrahlung cross section in electron-nucleus encounters

Inspired by the work of Pratt and coworkers on a sum rule for the polarization correlations in electron bremsstrahlung when the outgoing electron is not observed, we derive the corresponding sum rule for the elementary process of bremsstrahlung. This sum rule is valid for arbitrary electron wavefunctions provided the electron is emitted in the reaction plane. The numerical evaluation of this sum rule within the Dirac partial-wave theory for bare inert spin-zero nuclei and collision energies in the range of 1-10 MeV reveals violations for high nuclear charge. Such violations serve as a measure of the inaccuracies in the bremsstrahlung calculations.

physics.atom-ph↗
arXiv2021

Advances in bremsstrahlung: a review

Recent developments in bremsstrahlung from electrons colliding with atoms and nuclei at energies between 0.1 MeV and 500 MeV are reviewed. Considered are cross sections differential in the photon degrees of freedom, including coincidence geometries of photon and scattered electron. Also spin asymmetries and polarization transfer for polarized electron beams are investigated. An interpretation of the measurements in terms of the current bremsstrahlung theories is furnished.

physics.atom-ph↗
arXiv2020

On the excitation of the $2^+_1$ state in $^{12}$C in the $(e,e'γ)$ reaction

The excitation of the carbon $2^+$ state at 4.439 MeV by $70-150$ MeV electron impact and its subsequent decay to the ground state by photon emission is described within the distorted-wave Born approximation. The transition densities are obtained from the nuclear quasiparticle phonon model. The photon angular distributions are compared with earlier results and with experiment, including the influence of bremsstrahlung. Predictions for spin asymmetries in the case of polarized electron impact are also made.

nucl-th↗
arXiv2019

Excitation of the electric pygmy dipole resonance by inelastic electron scattering

To complete earlier studies of the properties of the electric pygmy dipole resonance (PDR) obtained in various nuclear reactions, the excitation of the 1$^-$ states in $^{140}$Ce by $(e,e')$ scattering for momentum transfers $q=0.1-1.2$~fm$^{-1}$ is calculated within the plane-wave and distorted-wave Born approximations. The excited states of the nucleus are described within the Quasiparticle Random Phase Approximation (QRPA), but also within the Quasiparticle-Phonon Model (QPM) by accounting for the coupling to complex configurations. It is demonstrated that the excitation mechanism of the PDR states in $(e,e')$ reactions is predominantly of transversal nature for scattering angles $θ_e \approx 90^o-180^o$. Being thus mediated by the convection and spin nuclear currents, the $(e,e')$ like the $(γ,γ')$ reaction, may provide additional information to the one obtained from Coulomb- and hadronic excitations of the PDR in $(p,p')$, $(α,α')$, and heavy-ion scattering reactions. The calculations predict that the $(e,e')$ cross sections for the strongest individual PDR states are in general about three orders of magnitude smaller as compared to the one of the lowest $2^+_1$ state for the studied kinematics, but that they may become dominant at extreme backward angles.

nucl-th↗
arXiv2018

Relativistic positron scattering from heavy ground-state nuclei

Cross sections and spin asymmetries for elastic positron scattering and for the emission of positron bremsstrahlung in collision with nuclei of zero and half-integer spin are calculated within the relativistic partial-wave theory. For elastic scattering, comparison is made with the respective results from electron scattering by 208Pb, 89Y and 23Na nuclei at high energies (up to 400 MeV). It is found that the difference between electron and positron intensities diminishes with energy, although the diffraction oscillations, which differ in phase for the two species, prevail up to the highest energies considered. Magnetic scattering strongly reduces the spin asymmetries for nuclei with spin, both for positrons and electrons. For the elementary process of bremsstrahlung the cross section, which is studied for the 197Au and 208Pb targets at low energies (1-30 MeV), increases with photon frequency for large scattering angles and small photon emission angles, in contrast to the usual behaviour of the doubly differential cross section, or of the triply differential cross section at small scattering angles.

physics.atom-ph↗
arXiv2009

The ground state of relativistic ions in the limit of high magnetic fields

We consider the pseudorelativistic no-pair Brown-Ravenhall operator for the description of relativistic one-electron ions in a homogeneous magnetic field B. It is shown for central charge not exceeding Z=87 that their ground state energy decreases according to the square root of B as B tends to infinity, in contrast to the nonrelativistic behaviour.

math-ph↗
arXiv2008

Heat kernel estimates and spectral properties of a pseudorelativistic operator with magnetic field

Based on the Mehler heat kernel of the Schroedinger operator for a free electron in a constant magnetic field an estimate for the kernel of E_A is derived, where E_A represents the kinetic energy of a Dirac electron within the pseudorelativistic no-pair Brown-Ravenhall model. This estimate is used to provide the bottom of the essential spectrum for the two-particle Brown-Ravenhall operator, describing the motion of the electrons in a central Coulomb field and a constant magnetic field, if the central charge is restricted to Z below or equal 86.

math-ph↗
arXiv2006

On the essential spectrum of the Jansen-Hess operator for two-electron ions

Based on the HVZ theorem and dilation analyticity of the pseudorelativistic no-pair Jansen-Hess operator, it is shown that for subcritical potential strength (Z < 90) the singular continuous spectrum is absent. The bound is slightly higher (Z < 102) for the Brown-Ravenhall operator whose eigenvalues are, by the virial theorem, confined to <2m if Z<50.math/m

math-ph↗