Electron-nucleus Bremsstrahlung Research Articles

Stellar cooling limits on light scalar boson revisited

We revisit the stellar cooling limits on the light scalar boson whose coupling to the Standard Model particles is described by its mixing with the Higgs boson. Strong constraints have been obtained from the electron-nucleus bremsstrahlung process (Ne→NeS) and the resonant plasma effect in the medium. We find that the bremsstrahlung contribution from the electron and nucleus scattering is of similar magnitude to the plasma mixing effect including the off-resonant mixing. The constraints on the scalar coupling are found to be about three orders of magnitude weaker than the previous evaluations because of the missing factor of the electron-nucleon mass ratio. For white dwarfs, the stellar cooling constraint is even more suppressed due to the Pauli blocking effect. We obtain limits on the Higgs-scalar mixing angle of 10−10–10−9, which are given by white dwarfs or red giants up to the luminosity limits, in the region where the scalar mass is lighter than about 10 keV.

Finite orbital-angular-momentum carried by the final electron and photon in plane-wave electron-nucleus bremsstrahlung

In quantum-electrodynamics scatterings the transfer of angular momentum between initial and final states can be resolved using the vortex scattering theory, where involved particles are described by quantum vortex states with featured orbital angular momentum (OAM). Here we employ the vortex scattering scenario in bremsstrahlung of a plane-wave electron by describing the final electron and photon in vortex states. We find that, while the total cross-section and angular distribution of the vortex scattering scenario are consistent with those from the ordinary plane-wave scattering, the final states in the former can gain non-negligible OAM values even though the incident electron does not contain any OAM. Moreover, introducing the OAM degree of freedom conserves the total angular momentum in polarized scattering. The dependence of the OAM on the opening angle of the vortex state and the energy ratio of photon to electron are obtained. It is shown that the emitted photon gains higher OAM at larger angles and energy ratios.

Inclusive electron scattering and the genie neutrino event generator

The extraction of neutrino mixing parameters from accelerator-based neutrino oscillation experiments relies on proper modeling of neutrino-nucleus scattering processes using neutrino-interaction event generators. Experimental tests of these generators are difficult due to the broad range of neutrino energies produced in accelerator-based beams and the low statistics of current experiments. Here we overcome these difficulties by exploiting the similarity of neutrino and electron interactions with nuclei to test neutrino event generators using high-precision inclusive electron scattering data. To this end, we revised the electron-scattering mode of the GENIE event generator ($e$-GENIE) to include electron-nucleus bremsstrahlung radiation effects and to use, when relevant, the exact same physics models and model parameters, as the standard neutrino-scattering version. We also implemented new models for quasielastic (QE) scattering and meson exchange currents (MEC) based on the theory-inspired SuSAv2 approach. Comparing the new $e$-GENIE predictions with inclusive electron scattering data, we find an overall adequate description of the data in the QE- and MEC-dominated lower energy transfer regime, especially when using the SuSAv2 models. Higher energy transfer-interactions, which are dominated by resonance production, are still not well modeled by $e$-GENIE.

An asymptotic DSM theory for high-energy near-tip bremsstrahlung

The Dirac–Sommerfeld–Maue theory for relativistic electron–nucleus bremsstrahlung at the short-wavelength limit is extended to cover an energy range from 0 to 3 MeV of the outgoing electron, irrespective of collision energy. This is achieved by using an asymptotic representation of the Sommerfeld–Maue function for the impinging electron, valid at energies above 50 MeV, as well as a partial-wave expansion for the final electronic state. The model is used to show that the analytical Sommerfeld–Maue theory is applicable for the calculation of the singly differential cross section, if the energy of the scattered electron exceeds about 3 MeV.

Inverse Compton scattering from solid targets irradiated by ultra-short laser pulses in the 1022–1023 W/cm2 regime

Emission of high energy gamma rays via the non-linear inverse Compton scattering process (ICS) in interactions of ultra-intense laser pulses with thin solid foils is studied using particle-in-cell simulations. It is shown that the angular distribution of the ICS photons has a forward-oriented two-directional structure centred at an angle ϑ =± 30°, a value which corresponds to a model based on a standing wave approximation to the electromagnetic field in front of the target, which only increases at the highest intensities due to faster hole boring, which renders the approximation invalid. The conversion efficiency is shown to exhibit a super-linear increase with the driving pulse intensity. In comparison to emission via electron-nucleus bremsstrahlung, it is shown that the higher absorption, further enhanced by faster hole boring, in the targets with lower atomic number strongly favours the ICS process.

Radiative electron capture to the continuum in U89++N2 collisions: Experiment and theory

For U89+ projectiles colliding at a beam energy of 75.91 MeV/u with a N2 target, we present a coincidence measurement between the cusp electrons emitted under an angle of 0∘ with respect to the projectile beam and the photons emitted under a polar angle of 90∘. This radiative-electron-capture-to-continuum cusp directly probes the theory of electron-nucleus bremsstrahlung up to the high-energy endpoint in inverse kinematics. In the present study, significant improvement with respect to the experimental accuracy has been achieved, resulting in a finer agreement between experimental and theoretical results.Received 10 December 2019Accepted 29 January 2020DOI:https://doi.org/10.1103/PhysRevA.101.022708Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasScattering of atoms, molecules, clusters & ionsScattering theoryAtomic, Molecular & Optical

Analytic calculations of electron–nucleus bremsstrahlung cross sections above a few MeV including higher-order corrections and multiple scattering in the target

Calculations of the elementary process of electron–nucleus bremsstrahlung employing a partial–wave expansion of the initial and final electron wave functions are exact and offer results that match the experimental data, but they become impractical for increasingly higher electron energies, especially in some regions of the emitted photon phase space. Here we take the opposite approach and use analytic expressions based on the Olsen–Maximon–Wergeland additivity rule, valid above few MeV, to decouple the calculation of the screening and Coulomb corrections. The former is obtained from the first Born approximation, while the latter is evaluated within the formalism of the Furry–Sommerfeld–Maue wave functions using the leading–order expression by Elwert and Haug and the next–to–leading–order corrections by Roche, Ducos, and Proriol, which is presently the best way to calculate cross sections for electrons with energies in the range of hundreds of MeV. A detailed discussion of the approximations involved and an extensive comparison with experimental data have been published in previous works. Here we focus on the numerical procedures that have been developed and on the stringent cross checks that have been performed to ensure the accuracy of the results. Published benchmark calculations for bremsstrahlung in a pure Coulomb field, that stop at 100 keV, are extended here to 100 MeV by making available selected values that could be used by other independent researchers to validate their programs. We also discuss the numerical details of the procedure adopted to convolve the bremsstrahlung cross section with the impinging electron angular distribution due to multiple scattering in the target.

Higher-order corrections to electron-nucleus bremsstrahlung cross sections above a few MeV

Higher-order corrections to electron-nucleus bremsstrahlung cross sections above a few MeV

Spectra and rates of bremsstrahlung neutrino emission in stars

We calculate the energy-differential rate for neutrino emission from electron-nucleus bremsstrahlung in stellar interiors taking into account the effects of electron screening and ionic correlations. We compare the energy-differential and the net rates, as well as the average $\bar{\nu}_e$ and $\bar{\nu}_x$ $(x = {\mu}, {\tau})$ energies, for this process with those for $e^{\pm}$ pair annihilation, plasmon decay, and photo-neutrino emission over a wide range of temperature and density. We also compare our updated energy loss rates for the above thermal neutrino emission processes with the fitting formulas widely used in stellar evolution models and determine the temperature and density domain in which each process dominates. We discuss the implications of our results for detection of $\bar{\nu}_e$ from massive stars during their pre-supernova evolution and find that pair annihilation makes the predominant contribution to the signal from the thermal emission processes.

Radiative-electron-capture-to-continuum cusp inU88++N2collisions and the high-energy endpoint of electron-nucleus bremsstrahlung

The radiative electron capture of a target electron into the projectile continuum has been studied for the collision system ${\text{U}}^{88+}+{\text{N}}_{2}\ensuremath{\rightarrow}{\text{U}}^{88+}+{[{\text{N}}_{2}^{+}]}^{*}+{e}^{\ensuremath{-}}+\ensuremath{\gamma}$ at 90 MeV/$\mathrm{u}$. Using a magnetic electron spectrometer, the energy distribution of cusp electrons emitted under an angle of ${0}^{\ensuremath{\circ}}$ with respect to the projectile beam and with a velocity close to the projectile velocity has been measured in coincidence with the emitted photons under various observation angles. The experimental results provide a stringent test for the corresponding process in inverse kinematics, namely, the theory of electron-nucleus bremsstrahlung at the high-energy endpoint. For comparison this process is calculated using fully relativistic Dirac wave functions and using semirelativistic Sommerfeld-Maue wave functions.

The importance of electron–electron bremsstrahlung for terrestrial gamma-ray flashes, electron beams and electron–positron beams

Thunderstorms emit terrestrial gamma-ray flashes with photon energies of up to tens of MeV and electron-positron beams that are created by photons with energies above 1.022 MeV. These photons are produced through the bremsstrahlung process when energetic electrons collide with air molecules. However, presently used cross sections for bremsstrahlung treat only the interaction of the electrons with the nuclei of molecules while we here include their interaction with shell electrons. We simulate the production of energetic photons by a negative stepped lightning leader, and we find that electron–electron bremsstrahlung contributes significantly, although the direct photon emission is less than from electron–nucleus bremsstrahlung. However, electron–electron bremsstrahlung also ejects shell electrons and therefore feeds the electron population above 1 MeV significantly. We find that it hence dominates the photon spectrum of the stepped lightning leader at 10 MeV.

Diffraction structures in high-energy electron–nucleus bremsstrahlung

Abstract The emission of hard bremsstrahlung during the collision of relativistic spin-polarized electrons with inert spin 0 and spin 1 2 nuclei is calculated within the weak-potential approximation. Diffraction structures in the polarization correlations between the beam electron and the emitted photon are predicted for collision energies in the region 50–120 MeV if the photon is emitted at backward angles. The dynamical recoil plays a dominant role concerning the location and the shape of the structures. The target nuclei 19F, 64Zn and 89Y are investigated.

Polarization correlations in electron-nucleus bremsstrahlung: the short-wavelength limit

The short-wavelength limit of the electron-nucleus bremsstrahlung is re-investigated with special emphasis on the polarization correlations between incoming electron and emitted photons. A theoretical analysis of these correlations is performed within both the rigorous relativistic Dirac theory and the Dirac-Sommerfeld-Maue (DSM) approach which approximates the initial electronic state by a Sommerfeld-Maue wavefunction. Based on detailed calculations carried out for bremsstrahlung of electrons scattered from medium- and high-Z bare ions, we argue that the DSM approach is complementary to the exact partial-wave theory at sufficiently high collision energies. For such high-relativistic domains predictions are made for the polarization correlations relating to linearly polarized radiation.

Cross section of electron-nucleus bremsstrahlung near the short-wavelength limit

Using the partial-wave formalism the cross section of bremsstrahlung for a pure Coulomb field is calculated for various atomic numbers of the target nucleus and various incident electron energies. The results are compared to those of previous theories. For intermediate and large atomic numbers the latter cross sections undervalue significantly the present ones. Except for low atomic numbers the cross sections in Born approximation with the Coulomb correction by Elwert yield more accurate results than the cross sections obtained by using the approximate Sommerfeld-Maue wave function. The effect of screening is small for low atomic numbers. At nonrelativistic energies the number of required partial waves is rather large for target nuclei with high atomic numbers, contrary to the expectations. The pertinent results exceed the numerical values including screening by factors of up to five. They verify the assumption that the nonrelativistic cross section of Sommerfeld is fairly accurate even for high atomic numbers.

Radiative electron capture to continuum (RECC) and the short-wavelength limit of electron–nucleus Bremsstrahlung in near-relativistic collisions

We report on simultaneous measurements of the continuum momentum distribution for RECC cusp electrons and bremsstrahlung in 90AMeV U88++ N2 → U88++ {N2+*} + ecusp(00) + hv (RECC) collisions. We show that x-ray photons which appear coincident with RECC cusp electrons stem from the short-wavelength limit of the electron-nucleus bremsstrahlung. The observed pronounced asymmetric cusp shape is in good agreement with theory within the relativistic impulse approximation. We expect that when exploiting the full imaging properties of our forward electron spectrometer, fully differential cross sections at the tip region of the bremsstrahlung spectrum with near 10−4 electron energy resolution are possible in the near future.

Radiative Electron Capture to the Continuum and the Short-Wavelength Limit of Electron-Nucleus Bremsstrahlung in90A MeVU88+(1s22s2)+N2Collisions

We have measured the continuum momentum distribution for radiative electron capture to the continuum (RECC) cusp electrons in 90A MeV U88+ + N2-->U88+ + N2 +* + ecusp(0 degrees ) + hnu (RECC) collisions. We demonstrate that x rays coincident with RECC cusp electrons originate from the short-wavelength limit of the electron-nucleus bremsstrahlung and explain the asymmetric cusp shape by comparison with theory within the relativistic impulse approximation.

The polarization of bremsstrahlung from radiative ionization induced by relativistic highly charged projectiles

Based on inverse kinematics the close relation between radiative electron capture to the projectile continuum, calculated within the impulse approximation, and electron–nucleus bremsstrahlung is shown. Particular emphasis is laid on the short-wavelength limit corresponding to cusp-electron emission in the target frame of reference. Differential cross sections and the degree of photon polarization are calculated for the coincident emission of electron and photon. Coplanar and non-coplanar geometries are considered, and the polarization is compared with that obtained from experiments on the elementary bremsstrahlung process and on radiative electron capture to bound states.

Current and future electron spectroscopy experiments in relativistic storage rings

Storage rings as the ESR and the future NESR in the FAIR project are unique tools to study the dynamics of electron-ion and ion-atom collisions in the realm of strong perturbations and short interaction times. A telling sign of the character of such collisions are the electrons emitted into the continuum. For high Z projectiles and low Z targets the projectile centred continuum is dominating. Precision studies of these electrons emitted in relativistic collisions thus are of paramount importance for an understanding of the ionization mechanisms active in transferring electrons into the continua. Forward electron spectroscopy thus appears to be the tool of choice. For high precision studies in collision spectroscopy of high Z projectiles we have implemented an imaging forward electron spectrometer into the ESR supersonic jet target zone. In combination with a reaction microscope to be implemented next this enables investigations of several fundamental processes ranging from kinematically complete studies of multiple ionization and (e,2e) on ions to radiative and non-radiative electron transfer processes to the projectile continuum and for the first time kinematically complete measurements of the short-wavelength limit of the electron nucleus Bremsstrahlung. We report first results.

Radiative Electron Capture to Continuum (RECC) in 90AMeV U88+(1s22s2) + N2: the Short Wavelength Limit of Electron Nucleus Bremsstrahlung

We have investigated the relation of forward emission cusp electron spectra and bremsstrahlung for 90AMeV U88+ + N2at the internal supersonic gas jet target of the ESR storage ring of GSI. We find that x ray photons measured in coincidence with cusp electrons originate from the short wavelength limit of the electron nucleus bremsstrahlung.

Bremsstrahlung during electron capture to continuum

Theoretical approaches for radiative ionization (RI) in energetic collisions of highly stripped projectiles with target atoms are reviewed and set into context with related processes. The interrelation between RI and electron-nucleus bremsstrahlung is displayed with the help of inverse kinematics. Particular emphasis is laid on the forward-peak region of the electron spectrum resulting from target electrons which are slowed down to approximately zero velocity in the projectile frame of reference. The forward-peak intensity and shape for RI is contrasted to the one obtained from nonradiative capture to continuum. The ridge in the photon spectrum related to forward-peak electrons can unambiguously be identified in measured doubly differential photon emission cross sections resulting from ion–atom collisions at relativistic impact energies.