Systematic photoabsorption cross sections studied within the axially deformed relativistic quasiparticle finite amplitude framework

DIRAC: A new version of computer algebra tools for studying the properties and behavior of hydrogen-like ions

Inclusive neutrino-nucleus cross sections are calculated using a consistent relativistic mean-field theoretical framework. The weak lepton-hadron interaction is expressed in the standard current-current form, the nuclear ground state is described with the relativistic Hartree-Bogoliubov model, and the relevant transitions to excited nuclear states are calculated in the relativistic quasiparticle random phase approximation. Illustrative test calculations are performed for charged-current neutrino reactions on $^{12}$C, $^{16}$O, $^{56}$Fe, and $^{208}$Pb, and results compared with previous studies and available data. Using the experimental neutrino fluxes, the averaged cross sections are evaluated for nuclei of interest for neutrino detectors. We analyze the total neutrino-nucleus cross sections, and the evolution of the contribution of the different multipole excitations as a function of neutrino energy. The cross sections for reactions of supernova neutrinos on $^{16}$O and $^{208}$Pb target nuclei are analyzed as functions of the temperature and chemical potential.

Since the nonrelativistic photoionization cross section decreases rapidly with an increase of the photon energy, the higher-order processes dominate in the formation of ions at larger values of photon energy. We carry out relativistic analysis of the second- and third-order processes. If the photon energy is large enough, the Compton scattering becomes the dominant mechanism for creation of ions. We show that the seagull term of the nonrelativistic Compton scattering amplitude can be viewed as the contribution of the negative-energy intermediate states in the relativistic amplitude. We obtain the general equations for the characteristics of the Compton scattering on the Bethe ridge and show their connection with equations of the impulse approximation. Employing the results obtained in Chap. 4, we obtain the differential distributions outside the Bethe ridge. We demonstrate the infrared stability of the sum of the contribution to the Compton scattering cross section coming from the soft scattered photons and the photoionization cross section that includes the radiative corrections. At still larger photon energies exceeding certain value \(\omega _0\), the ions are produced mainly accompanied by the creation of electron–positron pairs. We determine the energy distribution of the electrons ejected due to this mechanism. We calculate the dependence of \(\omega _0\) on the value of the nuclear charge Z for the single-electron ions and for the atoms containing Z electrons. We find also the photon energy region where this mechanism dominates in the creation of excited atoms.

An experiment was completed at the Stanford Linear Accelerator Center in which measurements of the (e,e{prime}p) coincidence quasielastic cross section in nuclei were extended to the largest possible Q{sup 2} attainable with the Nuclear Physics Injector and the End Station A spectrometers. Coincidence measurements of the quasielastic (e,e{prime}p) cross section were made on nuclei from carbon to gold in the Q{sup 2} range of 1-7 (GeV/c){sup 2}. Several papers describing the results were published or submitted. Analysis of the data is in its final stages. In summary, the cross section for quasielastic {sup 12}C(e,e{prime}p) scattering was measured at momentum transfer Q{sup 2}=1, 3, 5, and 6.8 (GeV/c){sup 2}. The results are consistent with scattering from a single nucleon as the dominant process. The nuclear transparency is obtained and compared with theoretical calculations that incorporate color transparency effects. No significant rise of the transparency with Q{sup 2} is observed. Cross sections were reported for the reaction {sup 2}H(e,e{prime}p)n for momentum transfers in the range 1.2 {<=}Q{sup 2}{<=}6.8 (GeV/c){sup 2} and for missing momenta from 0 to 250 MeV/c. The longitudinal-transverse interference structure function was separated at Q{sup 2}=1.5 (GeV/c){sup 2}. The observables were compared to calculations performed in nonrelativistic and relativistic frameworks. The data are best described by a fully relativistic calculation. The A-dependence of the quasielastic A(e,e{prime}p) reaction was studied with {sup 2}H, C, Fe, and Au nuclei at momentum transfers Q{sup 2}=1, 3, 5, and 6.8 (GeV/c){sup 2}. The nuclear transparency T A,Q{sup 2}, a measure of the average probability that the struck proton escapes from the nucleu A without interaction, was extracted. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as color transparency. No significant rise within errors is seen for any of the nuclei studied.

The nucleon-nucleon cross section in ground-state and colliding nuclear matter

Photoionization and photoabsorption cross sections of O, N 2, O 2, and N for aeronomic calculations

Results of a theoretical calculation of the differential cross sections of elastic proton-proton scattering at energies in the range 2–7000 GeV with two relativistic spin amplitudes are analyzed within the framework of the mathematical eikonal method. It is shown that taking account the contribution of heavy meson resonances improves the agreement between the theoretical calculations and the experimental data somewhat in the region of large momentum transfers.

We study the impact of the description of the knockout nucleon wave function on electron- and neutrino-induced quasielastic and single-pion production cross sections. We work in a fully relativistic and quantum mechanical framework, where the relativistic mean-field model is used to describe the target nucleus. The focus is on Pauli blocking and the distortion of the final nucleon, these two nuclear effects are separated and analyzed in detail. We find that a proper quantum mechanical treatment of these effects is crucial to provide the correct magnitude and shape of the inclusive cross section. Also, this seems to be key to predict the right ratio of muon- to electron-neutrino cross sections at very forward scattering angles.

Cross sections are presented for the reaction 2H(e,e’p)n for momentum transfers in the range 1.0 ≤ Q 2 ≤ 6.8 (GeV/c)2 and for missing momenta from 0 to 250 MeV/c. The longitudinal-transverse interference structure function has been separated at Q 2 = 1.2 (GeV/c)2. The observables are compared to calculations performed in non-relativistic and relativistic frameworks. The best description of the data is found using a fully relativistic treatment.KeywordsImpulse ApproximationFree NucleonReduced Cross SectionCerenkov DetectorStanford Linear Accelerator CenterThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Q{sup 2}=1, 3, 5, and 6.8 (GeV/c){sup 2}. The results are consistent with scattering from a single nucleon as the dominant process. The nuclear transparency is obtained and compared with theoretical calculations that incorporate color transparency effects. No significant rise of the transparency with Q{sup 2} is observed. Cross sections were reported for the reaction {sup 2}H(e,e{prime}p)n for momentum transfers in the range 1.2 {<=}Q{sup 2}{<=}6.8 (GeV/c){sup 2} and for missing momenta from 0 to 250 MeV/c. The longitudinal-transverse interference structure function was separated at Q{sup 2}=1.5 (GeV/c){sup 2}. The observables were compared to calculations performed in nonrelativistic and relativistic frameworks. The data are best described by a fully relativistic calculation. The A-dependence of the quasielastic A(e,e{prime}p) reaction was studied with {sup 2}H, C, Fe, and Au nuclei at momentum transfers Q{sup 2}=1, 3, 5, and 6.8 (GeV/c){sup 2}. The nuclear transparency T A,Q{sup 2}, a measure of the average probability that the struck proton escapes from the nucleu A without interaction, was extracted. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as color transparency. No significant rise within errors is seen for any of the nuclei studied.

Cross sections are presented for the reaction 2H(e,e′p)n for momentum transfers in the range 1.2≤Q2≤6.8(GeV/c)2 and for missing momenta from 0 to 250 MeV/c. The longitudinal-transverse interference structure function has been separated at Q2 = 1.2(GeV/c)2. The observables are compared to calculations performed in nonrelativistic and relativistic frameworks. The data are best described by a fully relativistic calculation.

Measurements and calculations for electron elastic differential cross sections (DCS) of argon atom in the energy range from 40 to 300 eV are presented. DCS have been measured in the crossed beam arrangement of the electron spectrometer with an energy resolution of 0.5 eV and angular resolution of 1.5∘ in the range of scattering angles from 20∘ to 126∘. Both angular behaviour and energy dependence of DCS are obtained in a separate sets of experiments, while the absolute scale is achieved via relative flow method, using helium as a reference gas. All data is corrected for the energy transmission function, changes of primary electron beam current and target pressure, and effective path length (volume correction). DCSs are calculated in relativistic framework by expressing the Mott’s cross sections in partial wave expansion. Our results are compared with other available data.

The absolute photoabsorption cross section of benzene (C6H6), encompassing the C 1s−1 π*e2u resonance, the C 1s threshold, the satellite thresholds, and extending up to 800 eV, has been measured using synchrotron radiation. Measurements of the discrete absorption structure from below the C 1s ionization threshold have been performed at high resolution. In order to unambiguously assign all structure present in the photoabsorption cross section, C 1s photoelectron spectra were measured from the C 1s threshold region up to 350 eV along with satellite spectra. The C 1s−1 single-hole and the satellite cross sections have been derived in absolute units, and their angular distributions have been determined. Resonant and normal Auger spectra were taken on the main features of the photoabsorption and single-hole cross sections. From the best resolved photoelectron spectra the underlying structure in the asymmetric benzene photoelectron peak can be partly disentangled. The experimental data show that at least two vibrational modes play a role in the C 1s photoelectron spectrum. The behavior of the investigated shake-up structure closely resembles that of ethene and ethyne, where the satellite bands due to π→π* excitations gain intensity towards threshold, an observation which may be attributed to conjugate shake-up processes. These processes lead to a significant contribution of the satellite intensity to the production of the absorption features traditionally assigned to the carbon shape resonances in benzene. An EXAFS analysis of the wide range oscillations present on the photoabsorption cross section has been performed, and reveals the C–C nearest-neighbor distance.

A new theoretical approach to spin-isospin excitations in open-shell nuclei is presented. The developed method is based on the relativistic meson-exchange nuclear Lagrangian of Quantum Hadrodynamics and extends the response theory for superfluid nuclear systems beyond relativistic quasiparticle random phase approximation in the proton-neutron channel (pn-RQRPA). The coupling between quasiparticle degrees of freedom and collective vibrations (phonons) introduces a time-dependent effective interaction, in addition to the exchange of pion and $\rho$-meson taken into account without retardation. The time-dependent contributions are treated in the resonant time-blocking approximation, in analogy to previously developed relativistic quasiparticle time blocking approximation (RQTBA) in the neutral (non-isospin-flip) channel. The new method is called proton-neutron RQTBA (pn-RQTBA) and applied to Gamow-Teller resonance in a chain of neutron-rich Nickel isotopes $^{68-78}$Ni. A strong fragmentation of the resonance along with quenching of the strength, as compared to pn-RQRPA, is obtained. Based on the calculated strength distribution, beta-decay half-lives of the considered isotopes are computed and compared to pn-RQRPA half-lives and to experimental data. It is shown that a considerable improvement of the half-life description is obtained in pn-RQTBA because of the spreading effects, which bring the lifetimes to a very good quantitative agreement with data.

Cross sections for the K-shell ionization of medium-heavy atoms by relativistic electrons have been calculated in a relativistic framework in the Coulomb gauge to order ${\ensuremath{\alpha}}_{0}$ (=${e}^{2}$/\ensuremath{\Elzxh}c) in the interaction Hamiltonian. Here exchange is neglected. The incident- and scattered-electron wave functions are described by Dirac plane waves. Only the bound- and ejected-electron wave functions are described nonrelativistically for a screened Coulomb potential, used earlier by the present authors. Thus the screening effect is taken into account in this calculation in a satisfactory manner. The calculation is a repetition of what has been published recently by the present authors with one important exception: Here, the ejected-electron continuum state wave function that is used is determined variationally for the above screened Coulomb potential. Thereby some perturbation approximation of ad hoc nature could be avoided. As a consequence, considerable improvement is noticed in the total cross-section results. Comparison with experimental results for $^{29}\mathrm{Cu}$, $^{47}\mathrm{Ag}$, and $^{79}\mathrm{Au}$ shows a good agreement. The calculation may easily be extended to ionization from other shells.