Total Cross Section Data Research Articles

INSIGHTS INTO THE π-p → ηn REACTION MECHANISM

A dynamical coupled channels formalism is used to investigate the η–meson production mechanism on the proton induced by pions, in the total center-of-mass energy region from threshold up to 2 GeV. We show how and why studying exclusively total cross section data might turn out to be misleading in pinning down the reaction mechanism.

Calculation and Evaluations for n + 54,56,57,58,natFe Reactions

All cross sections of neutron-induced reactions, angular distributions, energy spectra and double-differential cross sections are consistently calculated and analyzed for 54,56,57,58,natFe at incident neutron energies below 200 MeV based on the nuclear theoretical models, which are the optical model, preequilibrium and equilibrium reaction theories, and the distorted wave Born approximation theory. Theoretical calculated results are compared with existing experimental data and the evaluated results in ENDF/B-VII and JENDL-3. The optical model potential parameters are obtained according to the experimental data of total and nonelastic-scattering cross sections, and elastic-scattering angular distributions.

Low-energy positron scattering from methanol and ethanol: Total cross sections

We report total cross sections for positron scattering from two primary alcohols, methanol $(\mathrm{C}{\mathrm{H}}_{3}\mathrm{O}\mathrm{H})$ and ethanol $({\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H})$. The energy range of the present study is $0.1--40\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The ethanol measurement appears to be original while for methanol we compare our data to the only previous result from Kimura and colleagues [Adv. Chem. Phys. 111, 537 (2000)], with a significant discrepancy between them being found at the lower energies. Positronium formation threshold energies for both species, deduced from the present respective total cross section data sets, are found to be consistent with those expected on the basis of their known ionization energies. There are currently no theoretical results against which we can compare our total cross sections.

A global dispersive coupled-channel potential for the A = 24–122 mass range up to 200 MeV

A global dispersive coupled-channel optical model potential for the mass range of A = 24–122 is constructed up to 200 MeV incident energies. The local parameters for seven individual nuclei are searched by using the coupled-channel method based on the rigid-rotator model. The global forms of potential parameters are obtained by fitting those local parameters with simple functional forms of the target mass number. The numerical calculations show good agreement with available experimental data for neutron total cross sections, proton reaction cross sections, neutron/proton elastic and inelastic angular distributions, and proton elastic and inelastic analyzing powers.

Baryon polarization in low-energy unpolarized meson-baryon scattering

We compute the polarization of the final-state baryon, in its rest frame, in low-energy mesonbaryon scattering with unpolarized initial state, in unitarized BChPT. Free parameters are determined by fitting total and differential cross-section data (and spin-asymmetry or polarization data if available) for pK −, pK + and pπ+ scattering. We also compare our results with those of leading-order BChPT.

Geometric Scaling from Dokshitzer-Gribov-Lipatov-Altarelli-Parisi Evolution

We show that the geometric scaling of the total virtual photon-proton cross section data can be explained using standard linear Dokshitzer-Gribov-Altarelli-Parisi perturbative evolution with generic boundary conditions in a wide kinematic region. This allows us to single out the region where geometric scaling may provide evidence for parton saturation.

Assignments of Normally Unoccupied Orbitals to the Temporary Negative Ion States of Several Lanthanide NMR Shift Reagents and Comments on Resonance Involvement in Electron Circular Dichroism

We have measured the total electron scattering cross sections of several NMR shift reagent molecules X(hfc)3, where X = Yb, Er, Eu and Pr, by means of electron transmission spectroscopy (ETS) to determine their vertical attachment energies. A strong low-energy resonance (<1 eV) is observed in all of the compounds except for Yb(hfc)3. We explain this anomaly in terms of the ground-state electron configuration of each molecule. Also, with the aid of restricted open-shell Hartree-Fock (ROHF) calculations on analogous molecules with truncated fluorocarbon chains, we have assigned specific normally unoccupied orbitals to the resonances observed in ETS. To our knowledge, these molecules are the largest for which this procedure has been successfully completed. Nolting et al. (J. Phys. B 1997, 30, 5491) have demonstrated that the above NMR shift reagents exhibit electron circular dichroism (ECD) between 1 and 10 eV. Using our new total cross section data, we comment on the possibility of resonance involvement in the generation of ECD.

Theoretical Calculations of n + 232,234,236,238,240U Reaction Cross Sections

Consistent calculation and analysis of neutron scattering data of 232,234,236,238,240U with a spherical optical model, the unified Hauser-Feshbach theory and the exciton model, the linear angular momentum–dependent exciton state density model, and the coupled channel theory are carried above the resolved resonance range and below 20 MeV based on the experimental data of total, nonelastic-scattering, fission, and other reaction cross sections and elastic-scattering angular distributions. Theoretical calculations are compared with experimental data and other evaluated data from ENDF/B-VII and JENDL-3.3.

Theπ−p→ηnreaction at low energies in a chiral constituent quark model

A chiral quark-model approach is extended to the study of the $\ensuremath{\pi}N$ scattering at low energies. The process of ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}\ensuremath{\eta}n$ near threshold is investigated. The model is successful in describing the differential cross sections and total cross section near the \ensuremath{\eta} production threshold. The roles of the resonances in $n\ensuremath{\leqslant}2$ shells are clarified. Near threshold, the ${S}_{11}(1535)$ dominates the reactions, whereas the interferences from the ${S}_{11}(1650)$ turn out to be destructive around $W\ensuremath{\lesssim}1.6$ GeV. The ${D}_{13}(1520)$ is crucial to give correct shapes of the differential cross sections. The nucleon pole term contributions are significant. The ${P}_{11}(1710)$ plays an important role around the center-of-mass energy $W=1.7$ GeV, it is crucial to produce an enhancement in the region of $W&gt;1.6$ GeV as suggested by the data for total cross section. The $t$-channel is negligible in the reactions.

Comparison of halo of 11Be, 15C, and 19C

We have compared the halo of 11Be, 15C, and 19C nuclei by analyzing the one-neutron stripping reaction data on the Be target at 60-, 54-, and 57-MeV/A beam energies, respectively, within the framework of the eikonal approximation approach. The determination of effective range through the comparison of the total cross section data and prediction has revealed that the halo of 19C is the well developed, while that of 15C is the least and that of 11Be lies in between these two. The longitudinal momentum distribution data also strengthen these observations.

DIFFERENTIAL OPERATORS FOR SCATTERING AMPLITUDES

We discuss novel dispersion relations in differential form, connecting real and imaginary parts of elastic scattering amplitudes and formally valid at any energy above the physical threshold. By means of fits to total cross section data from proton-proton and antiproton-proton scattering, we evaluate the corresponding ratio ρ between the real and imaginary parts of the forward amplitudes. We show that the results are exactly the same as those obtained through standard integral dispersion relations.

High Energy p̄p and ppElastic Scatterings in QCD Inspired Model

We propose QCD inspired model to calculate p̄p andpp elastic scatterings at high energies in this paper. Acalculation for total cross section of p̄p and pp isperformed in which the contributions from gluon-gluon, quark-quark,and gluon-quark interactions are included. Our results show that theQCD inspired model gives a perfect fit to experimental data of totalcross section both for p̄p and pp elastic scatterings at thewhole energy region where experimental data existed at FNAL and CERN.

Study of proton total reaction cross section using a Helm model nuclear form factor

An analytic expression for proton–nucleus total reaction cross section has been developed within the framework of Coulomb modified Glauber multiple scattering theory using an approximate form of the Helm model form factor for the distributions of nucleons within nuclei. Without free parameters, the expression reproduces fairly well the proton total reaction cross section data at energies spanning 20–860 MeV. Excellent fits to the experimental data have been achieved using basically one free parameter, plus one other independent of beam energy.

Deuteron global optical model potential for energies up to 200 MeV

We present a set of new deuteron global phenomenological optical model potential parameters for nuclides in the mass range $12\ensuremath{\leqslant}A\ensuremath{\leqslant}209$ with incident energies from threshold up to 200 MeV, based on the experimental data of deuteron total reaction cross sections and elastic scattering angular distributions. The extracted deuteron global optical model potential parameters are compared to existing deuteron global optical potential.

Positron scattering from carbon dioxide

We report total cross section measurements for positron scattering from carbon dioxide $({\mathrm{CO}}_{2})$. The energy range of the present measurements is $0.1--20.0\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The present study is undertaken to both try and resolve a discrepancy in the literature between the earlier low-energy works of Hoffman et al. [Phys. Rev. A 25, 1393 (1982)] and Kimura et al. [J. Chem. Phys. 107, 6616 (1997)], and to extend the available data to lower energies. We find generally good agreement with the data of Hoffman et al. over the common experimental energy range. A comparison of the present data with available calculations is also made, as is a comparison with corresponding electron total cross section data.

The Re-Analysis of the 1700 MeV Structure of the P 11 Partial Wave Using the πN → KΛ Production Data

We have used the Breit-Wigner resonance model with S11, P11 and P13 resonances in the s-channel to re-analyze the old piN -> KLambda data with the aim to establish the origin of the prominent structure in the total cross section in the vicinity of 1700 MeV. In this paper we show that, at least in the Breit-Wigner resonance model, it is not possible to achieve the detailed reproduction of the narrow 1700 MeV total cross section peak using the standard partial widths. We have found the new set of resonance parameters enforcing the experimentally observed structure of the total cross section data simultaneously with the linear dependence of the differential cross sections with the cos(Theta) in the energy range 1650 MeV < W < 1800 MeV. The result is that the P13 partial wave has been strongly attenuated in this model. To understand the phenomenon, a much narrower width of a resonant state, the N(1710) P11 in our case, is required, but then the agreement of the model predictions with total cross section data at higher energies is lost. One way out is to allow for the existence of the second P11 resonance in that energy range. The same feature is shown by the polarization data. Analyzing the qqq or qqqq(qbar) nature of the recommended narrow P11 structure in the neighbourhood of 1700 MeV we re-open (remind of) the possibility that another P11 resonant state exists in addition to the standard N(1710) P11 PDG-resonance, and that one of the two states can be identified with the yet undiscovered cryptoexotic pentaquark state. To clarify the situation, we strongly recommend remeasurement of the piN -> KLambda process in the energy range 1650 MeV < W < 1800 MeV.

Room for anS=+1pentaquark inK+-nucleus phenomenology

Evidence for excitation of exotic $S=+1$ pentaquark degrees of freedom is presented by studying optical-potential fits to ${K}^{+}$-nucleus total, reaction and elastic-differential cross section data at ${p}_{\mathrm{lab}}~500\text{\ensuremath{-}}700$ MeV/c. Estimates of the underlying two-nucleon absorption ${K}^{+}\mathit{nN}\ensuremath{\rightarrow}{\ensuremath{\Theta}}^{+}N$ reaction cross section are made and are used for discussing the anticipated cross section of the strangeness exchange reaction ${K}^{+}N\ensuremath{\rightarrow}\ensuremath{\pi}{\ensuremath{\Theta}}^{+}$.

Positron and electron scattering from alkane molecules

Total cross-sections (TCSs) for 0.2–1000 eV positrons and 0.4–1000 eV electrons colliding with normal-octane and cyclo-octane molecules have been studied using a relative measurement method. The TCS curves for positron and electron vary smoothly and compare well with other alkane molecules, in order of increasing carbon number. For positron scattering, weak humps at 1.5–2.5 eV for both normal- and cyclo-octane were observed. In the energy range lower than 2.2 eV, positron TCSs are roughly equal to or larger than electron TCSs. For electron scattering, a resonance peak at 8 eV and a shoulder at 25.0 eV were observed for both molecules. Over all the energy range, the TCS values for normal-octane are larger than those of cyclo-octane. The positron and electron TCS data for normal- and cyclo-octane molecules are briefly compared with those for normal- and cyclo-hexane.

Parametrizations and dynamical analysis of angle-integrated cross sections for double photoionization including nondipole effects

Similarly to differential cross sections for one-electron photoionization, the doubly differential cross section for double photoionization (DPI) may be conveniently described by four parameters: the singly differential (with respect to energy sharing) cross section $({\ensuremath{\sigma}}_{0})$, the dipole asymmetry parameter $(\ensuremath{\beta})$, and two nondipole asymmetry parameters ($\ensuremath{\gamma}$ and $\ensuremath{\delta}$). Here we derive two model-independent representations for these parameters for DPI from a $^{1}S_{0}$ atomic bound state: (i) in terms of one-dimensional integrals of the polarization-invariant DPI amplitudes and (ii) in terms of the exact two-electron reduced matrix elements. For DPI of He at excess energies, ${E}_{\mathrm{exc}}$, of 100 eV, 450 eV, and 1 keV, we present numerical results for the asymmetry parameters within the framework of the convergent close-coupling theory and compare them with results of lowest-order (in the interelectron interaction) perturbation theory (LOPT). The results for ${E}_{\mathrm{exc}}=1\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ exhibit a nondipole asymmetry that is large enough to be easily measured experimentally. We find excellent agreement between our LOPT results and other theoretical predictions and experimental data for total cross sections and ratios of double to single ionization cross sections for $K$-shell DPI from several multielectron atoms.

Total and Capture Cross Sections of Dysprosium Isotopes up to 20 MeV

Neutron data for total and capture cross sections were evaluated on 160Dy, 161Dy, 162Dy, 163Dy, and 164Dy up to 20 MeV. The resolved resonance parameters were adopted from the Mughabghab compilation, but one bound level resonance for each isotope except 162Dy was invoked to reproduce the reference thermal cross sections. The average resonance parameters for s-wave neutrons were obtained from the analysis of the statistical behavior of resolved resonance parameters. Recent measurements of the capture cross sections were taken into account in adjusting the average resonance parameters for p- and d-waves. From the first excited energy to 20 MeV, the optical model, Hauser-Feshbach model, and quantum mechanical models were used to produce total, elastic scattering, and capture cross sections. The energy-dependent optical model potential was decided based on the recent experimental data. The calculated cross sections were in good agreement with the experimental data. The present evaluation resulted in improvement over the ENDF/B-VI.7 code.