High-energy Cross Sections Research Articles

Cross sections of the 3p-1 diagram and satellite Auger states in atomic calcium for electron impact

The Ca 3p ionization cross sections of the diagram Auger states 3p54s2 2P3/2,2P1/2 and of specific satellite Auger states were measured for electron impact from threshold up to 1.5 keV incident energy. Energies, multi-configuration compositions and relative high-energy cross sections of the Auger states were obtained theoretically by using the multi-configuration Hartree-Fock method including relaxation of outer electrons in the sudden approximation. For the cross section ratios of satellite Auger states relative to the diagram state 3p54s2 2P1/2 we found a strong energy dependence caused by the dynamics of shakeup transitions at low impact energies and, in addition, by strong admixtures of quartet state components. The experimental satellite-to-diagram cross section ratios at high impact energies agree well with the present calculation and with values obtained from photoionization data if the difference in the dynamics between photoionization and electron impact ionization is taken into account.

Shielding Benchmarks Analysis for Transport/Storage Casks

The dose rate measurements of the TN 12/2, TN 28 VT and FS 65 has been used to evaluate the calculational procedures of Transnucléaire (TN). The three-dimensional (3D) Monte Carlo code TRIPOLI-3.4 which is used to optimize the shielding of TN casks, is applied to the analysis of a series of benchmarks. In the same cases the one-dimensional (1D) Sn code SN1D and the point kernel code MERCURE-V (3D) used for the more simplified calculations, are checked by the comparison with the measurements. The multi-group approximation used by the above codes, in order to reduces nulear data, introduces errors due to the neutron cross-sections resonance treatment and the repartition of the gamma-ray spectrum (discrete) into an energy group structure. For a cask consisting of an iron shell of 250 mm of thickness, neutron dose rates can been underestimated of 50% if the resonances of the iron cross sections for high energy (above 1 MeV) are not taken into account. Also, depending on the energy group structure, gamma-ray dose rates can be over-estimated or under-estimated by the repartition of the gamma rays. The comparisons between measured and calculated dose rates are closer than 20% for the Monte Carlo calculations, 50% for the Sn calculations (1D) and a factor of 2 for the point kernel calculations.

Creation of relativistic positronium. II. Photoproduction cross sections including Coulomb corrections

Previous Born approximation calculations of the photoproduction of singlet (para) positronium are extended to give the cross section to all orders in the atomic number Z, i.e., to include Coulomb corrections. At the same time the cross section for triplet (ortho) positronium production---which does not exist in Born approximation---is obtained to all orders in Z. The calculations and results are given in a form closely related to the well-known high-energy pair production cross section including Coulomb corrections. The relations to pair production are discussed.

Photon-proton and photon-photon scattering from nucleon-nucleon forward amplitudes

We show that the data on $\ensuremath{\gamma}p$ and $\ensuremath{\gamma}\ensuremath{\gamma}$ interactions can be derived from the pp and $\overline{p}p$ forward scattering amplitudes using vector meson dominance and the additive quark model. The nucleon-nucleon data are parametrized using a model where high energy cross sections rise with energy as a consequence of the increasing numbers of soft partons populating the colliding particles. We present detailed descriptions of the data on the total and elastic cross sections, the ratio of the real to imaginary part of the forward scattering amplitude, and the slope of the differential cross sections for $pp,$ $\overline{p}p,$ $\ensuremath{\gamma}p,$ $\ensuremath{\gamma}\ensuremath{\gamma},$ $\ensuremath{\gamma}\stackrel{\ensuremath{\rightarrow}}{p}\ensuremath{\gamma}V$ and $\ensuremath{\gamma}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}{V}_{i}{V}_{j}$ reactions, where $V=\ensuremath{\rho},\ensuremath{\omega},\ensuremath{\varphi}$. We make a wide range of predictions for future DESY HERA and CERN LHC experiments and for $\ensuremath{\gamma}\ensuremath{\gamma}$ measurements at CERN LEP.

Lower energy consequences of an anomalous high-energy neutrino cross section

A new strong-interaction has been postulated for neutrinos above ~10^{19} eV to explain the production of highest-energy cosmic ray events. We derive a dispersion relation relating the hypothesized high-energy cross-section to the lower-energy neutrino-nucleon elastic amplitude. Remarkably, we find that the real forward amplitude becomes anomalous seven orders of magnitude lower in energy than does the total cross-section. We discuss possible measurable consequences of this early onset of new neutrino physics, and conclude that a significantly enhanced elastic \nu-N scattering rate may occur for the neutrino beams available at Fermilab and CERN.

Elastic cross sections for high energy hadron-hadron scattering

This report discusses some results on differential cross sections for high energy and small momentum transfer elastic hadron-hadron scattering in QCD, using a functional integral approach. In particulary a matrix cumulant expansion for the vacuum expectation values of lightlike Wegner-Wilson loops, which governs the hadronic amplitudes, is presented. The cumulants are evaluated using the model of the stochastic vacuum.

Differential cross sections for high energy elastic hadron-hadron scattering in nonperturbative QCD

Total and differential cross sections for high energy and small momentum transfer elastic hadron-hadron scattering are studied in QCD using a functional integral approach. The hadronic amplitudes are governed by vacuum expectation values of lightlike Wegner-Wilson loops, for which a matrix cumulant expansion is derived. The cumulants are evaluated within the framework of the Minkowskian version of the model of the stochastic vacuum. Using the second cumulant, we calculate elastic differential cross sections for hadron-hadron scattering. The agreement with experimental data is good.

Proton-nucleus cross section at high energies

Cross sections for proton inelastic collisions with different nuclei are described within the Glauber and multiple scattering approximations. A significant difference between the approximate `Glauber' formula and exact calculation with a geometrical scaling assumption for very high-energy cross section is shown. Experimental values of proton-proton cross sections obtained using extensive air shower data are based on the relationship of proton-proton and respective proton-air absorption cross sections. According to obtained results values reported by the Akeno and Fly's Eye experimental groups are about 10% overestimated. The proper energy dependence of absorption cross section for collisions with air nuclei is of a great importance for studies of high-energy cosmic rays using the Monte Carlo technique.

Differential cross sections for high energy elastic hadron-hadron scattering in nonperturbative QCD

Total and differential cross sections for high energy and small momentum transfer elastic hadron-hadron scattering are studied in QCD using a functional integral approach. The hadronic amplitudes are governed by vacuum expectation values of lightlike Wegner-Wilson loops, for which a matrix cumulant expansion is derived. The cumulants are evaluated within the framework of the Minkowskian version of the model of the stochastic vacuum. Using the second cumulant, we calculate elastic differential cross sections for hadron-hadron scattering. The agreement with experimental data is good.

Electron-impact ionization of atoms and ions from hydrogenic nl states

The dipole Bethe logarithmic constants for high-energy ionization cross sections of atoms and ions by electron impact have been calculated using the relation between and the bound-free Gaunt factor . By this method the values of are expanded to n = 50 and the constants calculated previously for the states 1s have been improved.

The calculation of high-energy photoionization cross sections for the Be isoelectronic sequence

R-matrix and distorted-wave calculations are carried out for photoionization for the Be-like ions Be I - Fe XXIII at high energies. Both methods include the inner-shell excitation process; in the R-matrix calculations these give rise to autoionizing resonances just below threshold for the onset of excitation from inner shells. Differences in the background cross section apparent for neutral Be become much less significant for the ionized species. The new calculations form a benchmarking exercise prior to upgrading the Opacity Project `TOPBASE' database for high energies.

Quark-quark scattering contributions to high-energy total cross sections

It is shown that total hadronic cross sections are described well by considering single- and double-scattering contributions from quark-quark scattering. With an energy-dependent form suggested by Regge theory, all high-energy total cross sections can be fitted successfully and efficiently using a small number of free parameters.

Higher-order corrections in the SM Higgs sector: the right scale

The evaluation of high-energy cross sections involving the SM Higgs boson requires the use of the Higgs running coupling $\lambda(\mu)$. Taking $\mu$ to be equal to the center-of-mass energy $\sqrt{s}$ of the scattering process, the perturbative approach fails for relatively small values of the Higgs mass and coupling, $\lambda(\sqrt{s})\approx 2.2$. Performing an approximate resummation of ``bubble'' Feynman diagrams, we find the scale $\mu=\sqrt{s}/ e \approx \sqrt{s}/2.7$ to yield reliable perturbative results, even for large Higgs mass and coupling. The new perturbative upper limit on the Higgs running coupling is $\lambda(\sqrt{s}/ e)\approx 4$.

Higher-order corrections in the SM Higgs sector: the right scale

The evaluation of high-energy cross sections involving the SM Higgs boson requires the use of the Higgs running coupling λ(μ). Taking μ to be equal to the center-of-mass energy √ s of the scattering process, the perturbative approach fails for relatively small values of the Higgs mass and coupling, λ(√ s ) ≈ 2.2. Performing an approximate resummation of “bubble” Feynman diagrams, we find the scale μ = √s e ≈ √s 2.7 to yield reliable perturbative results, even for large Higgs mass and coupling. The new perturbative upper limit on the Higgs running coupling is λ ( √s e ) ≈ 4 .

Channel-coupling effects in high-energy hadron collisions.

The two-gluon model of the Pomeron predicts strongly size-dependent high-energy hadron cross sections. Yet experimental cross sections for radially excited mesons appear surprisingly close in value. The strong coupling of these mesons in hadron collisions also predicted by the model permits a qualitative understanding of this puzzling behavior in terms of eigenmode propagation with a common eigen-$\ensuremath{\sigma}$. A detailed semiempirical coupled-channel model of the Pomeron is constructed to elucidate this and other features of high-energy hadron cross sections.

Positron impact ionization of He, Ne, and Ar

An ionization model containing a realistic description of the final state of the system, but employing only plane and Coulomb waves, is applied in positron ionization of helium, neon, and argon. This model was shown to agree perfectly with the earlier helium experiment of Fromme et al. for positron impact energies between 30–150 eV. Cross sections calculated with this model for impact energies up to 500 eV compare well with recent helium, neon, and argon measurements. Our work also shows that by improving the representation of the outgoing positron and electron one achieves a better agreement with the high-energy experimental cross sections.

An analytic theory of inclusive high-energy atomic reaction cross sections

We present a first Born approximate method for evaluating cross sections for collisions of one-electron projectile ions with one-electron target atoms. We consider those reactions in which the projectile electron is excited to a specific state but no measurement is made of the target electron in regard to its final disposition. Comparison with accurate first Born calculations is made. The approximation scheme involves evaluation of a one-dimensional integral. Explicit analytic forms are given for the asymptotic region. The method is applied to shed light on an interesting result obtained from the static mean field model.

Interaction cross sections and matter radii of A = 20 isobars

Abstract High-energy interaction cross sections of A = 20 nuclei (20N, 20O, 20F, 20Ne, 20Na, 20Mg) on carbon were measured with accuracies of ≈ 1%. The nuclear matter r.m.s. radii derived from the measured cross sections show an irregular dependence on isospin projection. The largest difference in radii, which amounts to approximately 0.2 fm, has been obtained for the mirror nuclei 20O and 20Mg. The influence of nuclear deformation and binding energy on the radii is discussed. By evaluating the difference in r.m.s. radii of neutron and proton distributions, evidence has been found for the existence of a proton skin for 20Mg and of a neutron skin for 20N.

Low-energy electron capture by C3+ from hydrogen using merged beams.

Measurements of absolute total cross sections for electron capture by ${\mathrm{C}}^{3+}$ in collisions with ground-state hydrogen and deuterium are reported in the energy range 0.3--3000 eV/u. In general, good agreement is obtained with published experimental measurements at the lower (10--110 eV/u) and higher (g1 keV/u) collision energies. However, the improved accuracy and the large energy range of these measurements made possible by the merged-beams technique indicate an energy dependence different than was suggested by interpolating previous published and unpublished measurements and by a theoretical calculation that attempted to reconcile the previous low- and high-energy total-capture cross-section data. The present measurements above 100 eV/u show excellent agreement with a more recent 22-state molecular-orbital calculation that predicts slight structure in the cross section at collision energies between 1000 and 2000 eV/u. Below 100 eV/u, the present measurements, which were performed with deuterium, deviate from an energy dependence suggested by earlier hydrogen measurements and by fully quantal calculations.

Nonperturbative corrections in resummed cross sections

We show that the resummation of large perturbative corrections in QCD leads to ambiguities in high energy cross sections that are suppressed by powers of large momentum scales. These ambiguities are caused by infrared renormalons, which are a general feature of resummed hard-scattering functions in perturbative QCD, even though these functions are infrared safe order-by-order in perturbation theory. As in the case of the operator product expansion, the contributions of infrared renormalons to coefficient functions may be absorbed into the definition of higher-dimensional operators, which induce nonperturbative corrections that are power-suppressed at high energies. The strength of the suppression is determined by the location of the dominant infrared renormalon, which may be identified explicitly in the resummed series. In contrast to the operator product expansion, however, the relevant operators in factorized hadron-hadron scattering and jet cross sections are generally nonlocal in QCD, although they may be expressed as local operators in an effective theory for eikonalized quarks. In this context, we verify and interpret the presence of $1/Q$ corrections to the inclusive Drell-Yan cross section with $Q$ the pair mass. In a similar manner, we find $\exp(-b^2\ln Q)$ corrections in the impact parameter space of the transverse momentum distributions of the Drell-Yan process and $e^+e^-$ annihilation. We also show that the dominant nonperturbative corrections to cone-based jet cross sections behave as $1/(Q\delta)$, with $\delta$ the opening angle of the jet and $Q$ the center of mass energy.