Elastic Cross Sections Research Articles

Rearrangement Collisions in the Schwinger Variational Principle: A Long-Standing Problem in Positron Scattering Physics.

In this letter, we propose a functional on the basis of the Schwinger variational principle that accounts for the particle rearrangement by solving a projected Lippmann-Schwinger equation system. The method is tested in the static-coupled approximation for positron-H, where excellent agreements with benchmark results are found for the elastic, positronium (Ps) formation and annihilation cross sections. The effect of virtual Ps formation is evidenced through the analysis of the annihilation map. A significant increase in the electron-positron density in the vicinity of the atom is obtained.

A Theoretical Study of Scattering of e± by Tl Atom

This article incorporates details of our calculations of the observable quantities for the scattering of electrons and positrons from a post transition metal Thallium (Tl), in the energy range of 1 eV ≤ Ei ≤ 1 MeV, using the relativistic Dirac partial wave (phase-shift) analysis employing a complex optical-potential. Absolute differential, integrated elastic and inelastic, transport, total ionization, and total cross sections and a thorough study of the critical minima in the elastic differential cross sections along with the associated angular positions of the maximum polarization points in the Sherman function are provided to study the collision dynamics. The optical potential model incorporates the interactions of the incident electron and/or positron with both the nucleus and the bound electrons of the target atom. In-depth analyses of the spin asymmetry, which are sensitive to phases related interference effect, brought on by the various ingredients of the lepton-atom interaction, are also presented. The performance of the current approach to explain the observations, with the exception of the extremely low energy domain, is shown by a comparison of the previous experimental and theoretical results on this target atom.

Electron interactions with analogous of DNA/RNA nucleobases: 3-hydroxytetrahydroFuran and α-Tetrahydrofurfuryl alcohol

We report quantitative results for electron induced molecular processes for DNA/RNA nucleobase analogous bio-molecules, 3-hydroxytetrahydrofuran (C4H8O2, 3hTHF) and α-tetrahydrofurfuryl alcohol (C5H10O2, THFA), which are similar in structure and functional group to backbone of DNA and RNA. We have employed spherical complex optical potential (SCOP) formalism to compute total elastic (Qel) and inelastic (Qinel) cross sections and used Complex Scattering Potential-ionization contribution (CSP-ic) method to obtain total ionization (Qion) and summed total excitation (∑Qexc) cross sections. These results obtained for a wide energy range (10 eV - 5 keV) may serve as the input parameters in predicting damage in biomolecular systems induced by secondary electrons caused by primary ionization radiation. We have observed a correlation between maximum Qion and molecular polarizability volume (α), ionisation energy (IE) and number of valence electrons (Nv). This work includes an attempt to estimate ∑Qexc for these molecules in normal state.

Scattering of e± by C2H6 Molecule over a Wide Range of Energy: A Theoretical Investigation.

The present work reports the theoretical investigation of the scattering of electrons and positrons by the ethane (C2H6) molecule over the energy range 1 eV-1 MeV. The investigation was carried out by taking into account the screening correction arising from a semiclassical analysis of the atomic geometrical overlapping of the scattering observables calculated in the independent atom approximation. The study is presented through the calculations of a broad spectrum of observable quantities, namely differential, integrated elastic, momentum transfer, viscosity, inelastic, grand total, and total ionization cross-sections and the Sherman functions. A comparative study was carried out between scattering observables for electron impact with those for positron impact to exhibit the similarity and dissimilarity arising out of the difference of the collisions of impinging projectiles with the target. Partial-wave decomposition of the scattering states within the Dirac relativistic framework employing a free-atom complex optical model potential was used to calculate the corresponding observable quantities of the constituent atoms. The results, calculated using our recipe, were compared with the experimental and theoretical works available in the literature. The Sherman function for a e±-C2H6 scattering system is presented for the first time in the literature. The addition of the screening correction to the independent atom approximation method was found to substantially reduce the scattering cross-sections, particularly at forward angles for lower incident energies.

Elastic and inelastic low-energy electron scattering from pyridine.

A comprehensive investigation of elastic and inelastic electron scattering from molecular pyridine is reported using the ab initio R-matrix method with the static exchange plus polarization and close-coupling approximations for incident energies up to 10eV. The two well-known low-lying 1 2B1 and 1 2A2 shape resonances as well as a 2 2B1 mixed-character resonance compare well with the theoretical and experimental results. We also detect five core-excited resonances (1 2A1, 1 2B2, 3 2B1, 2 2A2, and 4 2B1), which lie above the first electronic excitation threshold. The total elastic cross sections and momentum transfer cross sections agree reasonably with previous reference data. Comparisons of the differential elastic cross sections of pyridine with those measured for benzene, pyrazine, and pyrimidine show remarkable agreement at scattering angles above 40° but behave differently for forward scattering below 40° below 6eV, due to the dominant effect of the permanent dipole moment on the differential cross section in the low energy region with narrow scattering angles. Inelastic electronic excitation cross sections are presented, showing the influence of core-excited resonances below the ionization threshold for the first time.

Effect of mixing CF4 with O2 on electron characteristics of capacitively coupled plasma

Effect of mixing CF4 with O2 on electron parameters in capacitively coupled RF plasma was studied. Adding CF4 gas to fixed O2 flow, electron energy probability functions were measured by a Langmuir probe method. As the CF4 gas was added, the decrease in the probability of low energy electrons was observed. The proportion of low energy electrons decreased gradually as the CF4 gas ratio increased, respectively. From electron energy probability functions, electron densities and electron temperatures were calculated. As the CF4 gas ratio increased, electron density decreased and electron temperature increased. Collision cross sections of low energy electrons can explain electron parameter behaviors. By the strong electron attachment of fluorine species which were generated from CF4, low energy electrons depleted by attachment, and the overall electron temperature increased. However, as the elastic collision cross section of CF4 is not different from that of O2, the heating mechanism and physics of high energy electrons did not change.

Inelastic Channel Traces in Elastic Scattering Cross Sections in the \(d + {^{13}}\)C Reaction at 14.5 MeV

Inelastic Channel Traces in Elastic Scattering Cross Sections in the \(d + {^{13}}\)C Reaction at 14.5 MeV

Annihilation and nuclear elastic scattering of low-energy antiprotons

We perform a fitting procedure to differential elastic scattering cross section data of antiproton at intermediate energy on three different nuclei to evaluate parameters of a six-parameters Woods-Saxon optical potential. Then, with these values, we calculate the reaction cross sections at different momenta and evaluate the differential elastic cross sections for low-momenta antiproton ([Formula: see text]). We find that our analysis underestimates the reaction cross sections for data over the momentum-range 50 MeV/c to 1000 MeV/c. We predict measurable effect for antiprotons with momentum above 50 MeV/c at large angles ([Formula: see text]), in agreement with other recent results. Finally, we consider possible improvements to the model and the analysis.

Measurement of proton-carbon forward scattering in a proof-of-principle test of the EMPHATIC spectrometer

The next generation of long-baseline neutrino experiments will be capable of precision measurements of neutrino oscillation parameters, precision neutrino-nucleus scattering, and unprecedented sensitivity to physics beyond the Standard Model. Reduced uncertainties in neutrino fluxes are necessary to achieve high precision and sensitivity in these future precise neutrino measurements. New measurements of hadron-nucleus interaction cross sections are needed to reduce uncertainties of neutrino fluxes. We report measurements of the differential cross-section as a function of scattering angle for proton-carbon interactions with a single charged particle in the final state at beam momenta of 20, 30, and 120 GeV/c. These measurements are the result of a beam test for EMPHATIC, a hadron-scattering and hadron-production experiment. The total, elastic and inelastic cross-sections are also extracted from the data and compared to previous measurements. These results can be used in current and future long-baseline neutrino experiments, and demonstrate the feasibility of future measurements by an upgraded EMPHATIC spectrometer.

Systematic investigation of channel-coupling effects on elastic, inelastic, and neutron-transfer channels in Li6+Tb159

Elastic scattering angular distribution for weakly bound nucleus $^{6}$Li on the deformed rare earth $^{159}$Tb target nucleus has been measured at energies around the Coulomb barrier. The elastic scattering cross sections for this reaction consist of inelastic contributions from low lying excited states of $^{159}$Tb. The pure elastic cross-sections have been extracted from the admixture of elastic and inelastic data. The optical model potential parameters for the system have been obtained from the extracted pure elastic scattering cross sections. Coupled channel calculations have been performed with this set of potential parameters, to compare the theoretical and experimental inelastic scattering cross sections. The work has been extended to obtain the spectroscopic factor for $^{158}$Tb+n configuration from the experimental 1n-pickup data.

Cross sections for elastic collisions of low-energy positrons with tetrachloroethylene (C[formula omitted]Cl[formula omitted]) molecule

Elastic cross sections for positron scattering by tetrachloroethylene are being reported in this study. The calculations were carried out employing the Schwinger multichannel method at static plus polarization approximation, for impact energies up to 6 eV. To investigate the description of polarization effects, several calculations, with different polarization schemes, have been performed. In particular, we have investigated how the low-energy cross sections are affected by (i) increasing the number of particle and scattering orbitals; (ii) including additional functions placed in chargeless extra centers; (iii) including diffuse functions. The results at very low energy support the existence of a virtual state that becomes a bound state, as the polarization scheme is improved. The latter is in agreement with previous experimental and theoretical studies. Due to the lack of cross section data for this molecule, our present results are compared with experimental and theoretical data available in the literature for ethylene.

Joint theoretical and experimental study on elastic electron scattering from a methane molecule

We report on a combined experimental and theoretical study of elastic differential cross section DCS (E, θ) from methane molecule in the intermediate energy range (50-300eV), with experimental results limited to an angle interval of 25 to 125 degrees. Theoretical results are acquired using two approximations: a simple sum of individual atomic cross sections and the other with molecular effect taken into the account. The experimental setup based on a crossed beam technique comprising of an electron gun, a single capillary gas needle, and a detection system with a channeltron was used to measure differential cross sections. The absolute scale for the cross sections is obtained by a relative-flow method using argon gas as a reference. The dependence of DCS on the energy of incident electrons has been considered in detail. The results are analysed and compared with available theoretical and experimental data.

Lepton Universality Test with MUSE at PSI

Lepton universality (LU) typically refers to the lepton coupling, which is considered to be the same for e, μ, and τ leptons, if the interaction is electroweak according to the Standard Model, and it is hence a compelling probe for New Physics. The same principle of universal electroweak lepton interaction leads to the expectation that lepton scattering yields are equal for e and μ beams under the same kinematic condition. The mere mass difference between e and μ affects kinematic quantities (such as the relation between scattering angle and Q 2), and the lepton mass dependence of elastic cross sections for leptons scattered from structured and pointlike objects are taken into account. By comparing e +, e −, μ +, and μ − scattering yields, two-photon exchange (TPE) effects, universal or not, can be separated from the general LU test of the e/μ yield ratio. With its separable mixed beams of e +/μ + and e −/μ −, respectively, the MUSE experiment at PSI is not only designed to measure the proton charge radius with four lepton species, but is also uniquely suited to probe TPE and LU, while benefitting from partial cancellations of certain shared systematics. An overview will be given of the MUSE experiment, the sensitivity, and the present status.

Dielectric Breakdown Properties of He-H2 Mixtures for High Temperature Superconducting Power Devices

In this study, the electron energy distribution function (EEDF), the electron swarm parameters , the effective ionization coefficients, and the critical field strength (dielectric strength) in binary He-H2 gas mixture which is used as cryogenic for high-temperature superconducting power applications, are evaluated using two-term solution of the Boltzmann equation over the range of E/N ( the electric field to gas density) from 1 to 100 Td ( 1 Td=10-17 Vcm2) at temperature 77 K and pressure 2MPa, taking into account elastic ( momentum transfer) and inelastic cross-sections. Using the electron energy distribution function (EEDF) electron swarm parameters (electron drift velocity, mean electron energy, diffusion coefficient, electron mobility, ionization and attachment coefficient) are calculated. At low reduced electric field strength E/N, the EEDF is close to Maxwellian distribution, at high E/N, due to vibrational excitation of H2, the calculated distribution function is non-Maxwellian. Besides, the Boltzmann equation analysis showed as the small mole fraction of H2 in the He-H2 mixture is increased, the electron energy distribution function EEDF shifts to lower energy region, the density-reduced ionization coefficient α/N and density-reduced effective ionization coefficient (α-η)/N decreases, whereas density-reduced attachment coefficient η/N, density-reduced critical electric field strength increases, (E/N)crt and critical electric field Ecrt increases. It is found that dielectric field strength depends on pressure and temperature. To confirm the validity of the two term solution of Boltzmann equation analysis, a set of elastic and inelastic cross-sections for each gas He and H2 are used to calculate the electron swarm parameters and dielectric field strength. Compared with previous experimental and theoretical literatures, the values obtained are generally in good agreement.

Theory of QED radiative corrections to neutrino scattering at accelerator energies

Control over quantum electrodynamics (QED) radiative corrections is critical for precise determination of neutrino oscillation probabilities from observed (anti)neutrino detection rates. It is particularly important to understand any difference between such corrections for different flavors of (anti)neutrinos in charged-current interactions. We provide theoretical foundations for calculating these corrections. Using effective field theory, the corrections are shown to factorize into soft, collinear, and hard functions. The soft and collinear functions contain large logarithms in perturbation theory but are computable from QED. The hard function parametrizes hadronic structure but is free from large logarithms. Using a simple model for the hard function, we investigate the numerical impact of QED corrections in charged-current (anti)neutrino-nucleon elastic cross sections and cross-section ratios at GeV energies. We consider the implications of mass singularity theorems that govern the lepton-mass dependence of cross sections for sufficiently inclusive observables and demonstrate the cancellation of leading hadronic and nuclear corrections in phenomenologically relevant observables.

Sub Coulomb barrier d+ 208Pb scattering in the time-dependent basis function approach

We employ the non-perturbative time-dependent basis function (tBF) approach to study the scattering of the deuteron on 208Pb below the Coulomb barrier. We obtain the bound and discretized scattering states of the projectile, which form the basis representation of the tBF approach, by diagonalizing a realistic Hamiltonian in a large harmonic oscillator basis. We find that the higher-order inelastic scattering effects are noticeable for sub barrier scatterings with the tBF method. We have successfully reproduced experimental sub Coulomb barrier elastic cross section ratios with the tBF approach by considering only the electric dipole (E1) component of the Coulomb interaction between the projectile and the target during scatterings. We find that the correction of the polarization potential to the Rutherford trajectory is dominant in reproducing the data at very low bombarding energies, whereas the role of internal transitions of the deuteron projectile induced by the E1 interaction during the scattering becomes increasingly significant at higher bombarding energies.

Scattering of electrons and positrons from aluminum isonuclear series

The current study investigates the scattering of electrons and positrons from aluminum isonuclear series within the framework of the Dirac relativistic partial wave analysis. For the neutral aluminum atoms, the scattering phenomena are described by employing a short-range complex optical potential. For the ionic series, on the other hand, this potential is supplemented by the Coulomb potential. The calculations are reported for the differential cross-section, total cross-section, integrated elastic cross-section, inelastic cross-section, momentum transfer cross-section, viscosity cross-section, and total ionization cross-section over the energy range 1 eV ≤ E i ≤ 1 MeV. The Sherman function S and spin asymmetry parameters T and U are also predicted for the same scattering systems over the same energy range. In addition, for the first time, we report a systematic study of the critical minima in the differential cross sections as well as the associated maximum spin polarization points in the Sherman function. We also compute the inelastic, elastic, momentum transfer, viscosity and total mean free paths for the aforesaid scattering systems. The Coulomb glory effect, the amplification of elastic backscattering of electrons from positive ions, is examined throughout the ionic series of aluminum. A comparison of our results to the reported theoretical and experimental studies reveals a good consistency over the compared energy range. The present theoretical method is thus expected to be useful for the fast generation of accurate cross-sections needed in many areas of science, technologies, and industries.

Analysis of Elastic Scattering Cross-Sections of Carbon Isotopes (10–16C) Using Different Nucleon-Nucleon Interactions

In this study, the comparative analysis of different nucleon-nucleon interactions is carried out in the framework of the optical model. The real potential is obtained using the double folding model for eight different nucleon-nucleon interactions which consist of B, G1, G2, SL, R3Y(HS), R3Y(Z), R3Y(W), and R3Y(L1). The results are compared with M3Y nucleonnucleon results, as well as the experimental data in order to perform a comparative study. The similarities and differences of the nucleon-nucleon interactions are discussed, and alternative nucleon-nucleon interactions are proposed for the analysis of carbon isotopes (10-16C).

Electronic Excitations and Low-Energy Electron-Induced Scattering Studies of Acrylonitrile (CH2CHCN).

We report here theoretical investigations on structural, spectroscopic, and electron scattering for acrylonitrile (CH2CHCN), a molecule of importance in astrochemistry as well as the chemical industry. Quantum chemical calculations for ground and excited states are performed using density functional theory (DFT) and time-dependent-DFT methods, respectively. The results of geometry optimization and vibrational frequencies agree well with data available in the literature, while vertical excited singlet-state energies are extended to higher excited states as compared to earlier studies, including Rydberg and valence excitations. Quantum defect analysis and comparison of the theoretically predicted energies with earlier reported experimental works led to the confirmation of some spectral assignments and the revision of a few assignments. Vibrational frequencies calculated for the cationic ground state are used to tentatively assign vibrational bands appearing along with the Rydberg transitions. Triplet excited-state energies for which no data is available in the literature are reported here for the first time. Low-energy (0.1 to 20 eV) electron scattering calculations are performed using the ab initio R-matrix method. Several types of resonances are predicted in the energy-dependent elastic cross-section, most of which are in good agreement with earlier experimental or theoretical works, while a few new resonances are found above 6 eV. Additionally, calculations of eigenphase sum, differential, momentum transfer, electronic excitation, ionization, and total cross-sections are being reported for the first time. This work represents a comprehensive theoretical study of the electronically excited states as well as low-energy electron scattering of acrylonitrile, which would be useful for understanding its chemistry in the interstellar medium as well as industrial applications.

Low-Energy Positron Scattering by Pyridine and Aniline.

Calculated differential and integral cross sections for elastic scattering of low-energy positrons by pyridine and aniline are presented here. The cross sections were obtained using the Schwinger multichannel method in the static-plus polarization approximation, and the Born closure procedure was employed to account for the long-range potential due to the permanent dipole moment of the molecule. The elastic integral cross sections are compared with available theoretical and experimental data for the same molecules finding an overall good agreement. The present results are also compared with available calculated cross sections for the close-related molecules benzene and pyrimidine, where an overall similar angular behavior of the differential cross sections is found.