Total Cross Section Data Research Articles

Model-independent determination of [formula omitted] from τ-like decays in e+e− and implications for chiral symmetry

We determine the strange quark running mass of the MS -scheme by simulating τ-like inclusive processes for the old Das-Mathur-Okubo sum rule relating the e + e − into I = 0 and I = 1 hadrons total cross-sections data. We obtain to three-loop accuracy: m s(1 GeV) = (197 ± 29) MeV. By combining this result with the pseudoscalar sum rule estimate of ( m d + m u ) and the standard current algebra values of the light quark mass ratios, we deduce: m d(1 GeV) = (10 ± 1) MeV, m u(1 GeV) = (4 ± 1) MeV, and built1 2 〈 uu + dd〉(1 GeV) = − [(229 ± 9) MeV] 3 . Using also this new value of m s , we also re-estimate the (pseudo) scalar two-point correlator subtraction constants, from which we deduce a deviation of about 34% from kaon PCAC and a value of 0.7 −0.3 +0.1 for the ratio 〈 ss〉 〈 uu〉 of the normal-ordered condensates, which, therefore, confirm previous findings from QCD spectral sum rules. Finally, using the recent two-loop value of m b from the ϒ-sum rules, we obtain the scale independent quark-mass ratio: m b m s = 34 ± 4 .

State-to-state crossed molecular beam measurements for collision processes in Na/Na +, K + and Cs + systems

State-to-state excitations to Na(3p 2P 1/2,3/2) have been studied by the crossed molecular beams technique in collisions between Na(3s) atoms and Na +, K + and Cs + ions, in the 0.2–3 keV collision energy range. Measurements of charge transfer excitations leading to Cs(7p 2P 1/2,3/2) have also been obtained for the two doublet components at higher collision energies. In both cases, the branching ratio between the two J levels as a function of inverse velocity are qualitatively analyzed in terms of the properties of the potential energy curves assumed for such collisional systems. The weakness of the luminescence signals measured for higher direct excitations decaying to Na(3p) states in NaCs + collisions makes negligible the cascade effect corrections in the total cross-section data for the Na(3s) → Na(3p) excitation process previously reported, for which a preliminary theoretical approach is discussed.

On the coherence between high-energy total cross-section data when compared with general principles

We perform an essentially model-independent study of the internal coherence between high-energy total cross-section data by using classes of functions satisfying general principles. Our study is practically independent of the ϱ-parameter values. Our general analysis, made without any fit, reveals certain inconsistencies in the existing set of high-energy data. Some of these inconsistencies are eliminated by giving up arbitrary assumptions sometimes made in “fitology”. We conclude that the ln 2 s increase of total cross-sections at high energies is clearly favoured when compared with the other possible behaviours.

Atomic data for opacity calculations. XXI. The neon sequence

Photoabsorption processes are studied for the ground and excited terms of the members of the neon isoelectronic sequence considered to be of significant astrophysical abundance. A two-state, LS close-coupling calculation is carried out. Oscillator strengths and total photoionization cross section data are calculated for even and odd LS terms with S=0,1;L<or=4, and an effective principal quantum number nu <or=10.

Total cross section measurements for positrons and electrons colliding with molecules. I. SiH4 and CF4

Total cross sections (TCSs) for 0.7-400 eV positrons and 1.0-400 eV electrons colliding with mono-silane (SiH4) and tetrafluoromethane (CF4) molecules have been obtained by relative measurements. The TCS curve of e+-SiH4 with a broad minimum around 3.5 eV is fundamentally similar to that of e+-CH4. TCSs of e+-SiH4 below 20 eV are higher than the theoretical values. The TCS curve of e+-CF4 is different from the curve of e+-SiH4. The TCS data of e--SiH4 from 3 to 20 eV are lower than the theoretical data from 3 to 20 eV. The TCS curve of e--SiH4 shows the shape resonance at 3.1 eV, and is also similar to that of CH4. Also, the TCS curve of e--CF4 has more complicated structures.

Crossed molecular beams study of the M +( 1S)+Na(3 2S)→M +( 1S)+Na(3 2P) collision systems (M +=Li +, Na +, K +, Cs +) in the 0.05–3.00 keV energy range

An apparatus is described for the study of atomic electronic excitation processes in collisions between alkali ions and neutral alkali atoms. A thermal atom beam is crossed with an ion beam at energies varying from 0.05 to 3.00 keV and the fluorescence from the decay of excited atomic states formed by collision is measured (specifically in this paper the D-lines from Na(3 2P)). We report the apparatus construction, its calibration against previous data for the Li +Na system, total cross section data for Na +Na and K +Na for an energy range extended up to 3.00 keV, and new data for the Cs +Na system, which shows a broad maximum in the energy dependence of cross section between 1.50 and 2.00 keV.

Total nuclear photoabsorption cross section in the range 0.2-1.0 GeV for nuclei throughout the periodic table

An analysis of the total photoabsorption cross section for nuclei ranging from 4He up to 238U has been performed in the energy range 0.2-1.0 GeV. Mean total photoabsorption cross sections have been obtained by summing up the contributions from partial photoreactions, and found to follow an A1-dependence in the 0.2-1.0 GeV range. A review of the available total photoabsorption cross section data is also presented. Comparisons have been made with cross section values calculated by considering both the quasi-deuteron and π-meson photoproduction mechanism of primary nuclear photointeraction.

Δ Excitations in nuclei and the coherent pion decay

The Δ excitations in nuclei induced by intermediate energy charge exchange reactions are analyzed within the isobar-hole model. It is shown that the isovector spin-longitudinal (S · qT) response function of nuclei in the Δ resonance region is shifted down in energy by ~ 60 MeV in comparison to the spin-transverse (S × qT) response function. This shift is consistent with pion and photon total cross section data. The coherent pion decay of the Δ resonance is studied by means of the 12C(p, nπ+)12C(g.s.) coincidence reaction. The calculations show that the coherent pion production cross section provides a unique signature on the nuclear pionic mode. The coherent pions have a peak energy of E = 250 MeV and a strongly forward peaked angular distribution.

Pion production near threshold

The production of pions in nucleon-nucleon collisions has recently attracted renewed attention because of the advent of highly precise, near-threshold total cross section data in three different channels, and because of the apparent failure of conventional theory to reproduce the magnitude of the s-wave production cross section, leading to the speculation that we might learn something new about the pion field of a nucleon. The onset of higher partial waves is observed in differential cross section and analyzing power measurements. The measurement of spin correlation coefficients close to threshold will become possible in the near future in storage rings with electron cooling and internal targets. Recent data on pion production in the three-nucleon system support the importance of a quasi-free production of pions from nuclei.

Analysis of total neutron-nucleus cross sections using relativistic impulse approximation.

We have used the relativistic impulse approximation (RIA) to study the newly measured neutron total cross section data for [sup 208]Pb, [sup 90]Zr, and [sup 40]Ca. In particular, we are interested in what we can learn from the RIA in order to build up a phenomenological optical potential. A complete set of scattering observables would be required in order to study the details of the neutron-nucleus interaction. In the absence of any such data at intermediate energy, the present study of total cross sections provides useful preliminary information on the isovector part of a generalized nucleon-nucleus interaction. We used the [ital NN] amplitude calculated by McNeil, Ray, and Wallace (MRW) and the relativistic Love-Frany [ital NN] amplitude developed by Murdock and Horowitz (MH). We found that the use of MH's amplitude in the RIA gives a good description to the neutron total cross section from 200 to 400 MeV, while the use of MRW's amplitude provides a good description from 500 MeV and above. The energy dependence of the volume integrals of the total optical potential is consistent from both calculations, but there is a large difference in the energy dependence of the volume integral of the isovector part ofmore » the potential.« less

Extraction of total cross section data for the pi -p--> pi + pi -n reaction.

Total cross section extractions are sometimes based on extrapolations of in-plane data to unobserved regions of phase space. The total cross section can then only be derived if assumptions are made about the distributions of the independent phase space variables. In the case of the reaction ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$n an out-of-plane measurement, performed by our group, indicates that these assumptions made by some experimenters are partially not supported by the data.

Extrapolation of hadron cross sections to supercollider energies within the two-component dual parton model.

In the framework of a two-component dual parton model we perform a fit to $p\overline{p}$ total, elastic, inelastic, and single-diffractive cross-section data at collider energies. The fit including diffractive data gives better results using the supercritical soft Pomeron instead of the critical one. Because of the different structure function parametrizations the predictions of cross sections at supercollider energies are subject to large uncertainties.

Phase-shift analysis of neutron-208Pb scattering and mean-field studies.

The existing n${\mathrm{\ensuremath{-}}}^{208}$Pb elastic differential cross section, analyzing power, and total cross-section data in the energy range from 4 to 30 MeV were analyzed via a phase-shift analysis in order to find out how well these data are suited for dispersion relation based mean-field studies. It was found that the data can be well described by the phase-shift method and that overlapping resonances are likely to be responsible for deviations between the data and the fits obtained in recent optical-model analyses using the dispersion relation approach.

High-resolution neutron total and capture cross sections in 67Zn

High-resolution measurements of the neutron total and capture cross sections have been performed on the separated isotope 67Zn in the energy range from a few keV to about 1 MeV using the neutron time of flight technique and the pulsed Oak Ridge Electron Linear Accelerator. From R-matrix analysis of the total cross section data up to approximately 180 keV and least-squares fitting of capture data up to approximately 24 keV, values of E0, g Gamma n, Jpi and Gamma gamma 0 for resonances have been obtained. These results have provided the following values of average quantities: (S0J=2(*104)=(1.35+or-0.15), S0Jk=3(*104)=(2.23+or-0.34) and S0J=2.3(*104)=(1.86+or-0.20) up to 180 keV), (D0J=2=(1.09+or-0.06) keV, D0J=3=(0.83+or-0.04) keV and D0J=2.3=(413+or-28) eV up to 50 keV), (S1(*104)=(0.72+or-0.07) and D1=(137+or-14) eV up to 24 keV). The value of average radiation width is (0.44+or-0.06) eV for 47 s-wave resonances up to approximately 24 keV.

Anisotropic low energy electron collision cross sections for methane derived from transport coefficients

Based on a comprehensive set of transport parameters of electrons in methane derived from single electron spectra in the range of field 0.01-15 Td the authors determined a set of elastic and inelastic scattering cross sections up to 3 eV. The necessity to include anisotropic elastic scattering in a Boltzmann analysis of methane is demonstrated. In addition the drift velocity in a mixture of methane with helium was used to enhance the reliability of the derived cross sections. The low energy part of the cross sections for elastic scattering is subject to a MERT analysis and is compared with total cross section data from single scattering experiments.

Direct and valence neutron capture by 7Li.

We have measured the cross section for neutron radiative capture by {sup 7}Li at thermal neutron energy as 45.4{plus minus}3.0 mb. We have compared this value, and the available fast-neutron-capture cross-section data on {sup 7}Li, with direct- and valence-capture theory. The mechanism of direct capture involving simple neutron-orbital transitions within a potential well can adequately account for the magnitude of the thermal-neutron-capture cross sections and the shape of the fast-neutron-capture cross sections. We recommend that the capture cross sections from the theoretical calculation, instead of those from a recent measurement, be used for nuclear astrophysics calculations. If the fast-neutron-capture data are normalized at 25 keV to the theoretical value, the magnetic-dipole ({ital M}1) radiation width of the 255-keV {ital p}-wave resonance can be deduced. It is in agreement with the value calculated from a valence theory for {ital M}1 capture, thus lending support for this neutron-capture mechanism as an important one, at least for light nuclei. We also find some evidence from our analysis of the total cross-section data for a possible energy dependence of the potential required to describe the almost pure single-particle {ital s}-wave resonances underlying the {sup 7}Li cross section.

The Ne–O2 potential energy surface from high-resolution diffraction and glory scattering experiments and from the Zeeman spectrum

The full anisotropic potential energy surface for the Ne–O2 van der Waals molecule has been obtained from the simultaneous analysis of total differential cross section data with well resolved diffraction oscillations and of absolute total integral cross section data with glory structure measured in Perugia, of the Zeeman spectrum measured in Nijmegen, and of transport coefficients taken from literature. The anisotropy of the interaction is obtained from the Zeeman spectrum using both numerical and analytical approaches for the energy levels, and from the quenching of the diffraction oscillations in the total differential cross section within the infinite-order-sudden approximation. The latter approximation is practically exact under the experimental conditions, as previously shown for the similar Ne–N2 system by comparison with exact close-coupling scattering calculations. The derived potential energy surface represents a dramatic improvement with respect to a previous approximate estimate.

Scattering of polarized and unpolarized neutrons from 93Nb from 8 to 17 MeV and optical model descriptions.

Differential cross sections and analyzing powers for neutron elastic scattering from $^{93}\mathrm{Nb}$ have been measured at energies from 8 to 17 MeV using pulsed-beam time-of-flight methods. These data plus total cross-section data from 1 to 20 MeV are interpreted in terms of the spherical optical model. Several sets of optical potential parameters with systematic energy dependences have been derived in searches that used different initial parameter sets. In addition, comparisons of the data to calculations based on previously reported optical potentials are presented. It is concluded that the data favor the inclusion of a small imaginary spin-orbit term.

Thermal n-d radiative capture

The impulse-approximation and pion-exchange current contributions to the radiative capture of thermal neutrons by deuterium have been calculated using initial- and final-state wave functions generated by solving the configuration-space Faddeev equations for several nucleon-nucleon and nucleon-nucleon-plus-three-body-force hamiltonian models. Numerical results are compared with previously published total cross section data and with recent measurements of the M1 photon polarization and the spin-quartet capture fraction.

N+209Bi mean field between -20 and 60 MeV.

New measurements of differential elastic neutron scattering for {sup 209}Bi at energies between 7.5 and 24.0 MeV are presented along with new measurements of {sigma}{sub {ital T}} up to 60 MeV. These data, taken together with earlier measurements at lower energy, provide a very large data set for testing and extending the dispersive optical-model analysis. The dispersion correction to the optical model has been obtained from the scattering and total cross-section data. The potential is extrapolated to negative energy for comparison with bound-state properties. A very good description of all of the data is obtained from {minus}20 to +60 MeV. The present analysis suggests somewhat less depletion of the Fermi sea in this mass region than has been obtained from electron-scattering data and from other recent treatments of the dispersion correction to the optical model.