Ratio Of Differential Cross Sections Research Articles

Coherent control of resonance-mediated reactions: F+HD.

Cross sections resulting from scattering that proceeds via an intermediate resonance are shown to be exceptionally controllable using a coherent superposition of only two initial states. Full quantum computations on F+HD(v=0;j=0,1)-->H+DF, D+HF, which exhibits a resonance in one of the reactive channels, support the formal arguments, showing that control is indeed vast. In this case the ratio of reactive integral cross sections can be altered by a factor of 62 (compared to a noncoherent factor of only 3.3), while the ratio of reactive differential cross sections can be altered by a factor of over 6000 (compared to a noncoherent factor of less than 7). These results constitute the first prediction of extensive quantum control in a collisional process.

Low-energy electron scattering from atomic hydrogen. II. Elastic and inelastic scattering

We present measurements of differential cross sections for elastic electron scattering from atomic hydrogen at 20 eV and 40 eV incident electron energies and ratios of differential cross sections for electron-impact excitation of atomic hydrogen to the $n=2,$ 3, and 4 levels at incident electron energies of 14.6 eV, 15.6 eV, 17.6 eV, 20 eV, 25 eV, and 40 eV with scattering angles ranging from $10\ifmmode^\circ\else\textdegree\fi{}$ to $130\ifmmode^\circ\else\textdegree\fi{}.$ We compare our results to available experimental measurements and recent convergent close-coupling calculations. Our results resolve significant discrepancies that existed between theory and past experiments.

Angular dependence of coherent to incoherent scattering differential cross-section ratios for Zr, Nb and Mo elements

The ratios of differential cross-section for coherent and incoherent scattering of 59.5 keV γ-rays for Zr, Nb and Mo scatterers were experimentally determined for 20 scattering angles between 40° and 135° by using a high-resolution Si(Li) detector. The ratio of these cross-sections can be determined with higher precision than absolute differential cross-sections since these values are independent of some geometrical parameters and calibration. The corresponding theoretical coherent to incoherent scattering differential cross-section ratios were calculated by means of non-relativistic form factors, relativistic form factors, relativistic modified form factors and incoherent scattering functions. The calculated results were compared with the experimentally measured results to check the applicability of the theories of incoherent scattering function and form factor.

Measurements of Differential and Doubly-Differential Cross-Sections for Electron Impact Elastic Scattering, Excitation, and Ionization of Atomic Hydrogen

Accurate, normalized doubly-differential cross-sections, differential cross-section ratios and relative differential cross-sections for electron impact ionization, excitation to the H(n = 3,4) levels and elastic scattering of atomic hydrogen have been measured at incident electron energies ranging from 14.6 to 40 eV for scattering angles of 10° to 130°. The measurements are normalized to the accurate differential cross-section for electron impact excitation of H(n = 2) from the convergent close-coupling theory, which has recently been shown to be accurate within 10%. Our measurements show very good agreement in comparison with the most recent theoretical models viz. the Convergent Close-Coupling (CCC) model and the Exterior Complex Scaling (ECS) model.

Electron impact excitation of the argon3p54s configuration: differential cross-sections and cross-section ratios

New electron-impact differential cross-section (DCS) and DCS ratiomeasurements for the excitation of the four levels making up the3p54s configuration of argon are reported at incident electron energies of 14, 15, 17.5, 20,30, 50 and 100 eV. These cross-sections were obtained using a conventional highresolution electron spectrometer. Elastic electron scattering from argon was usedas a calibration standard. Electron–helium DCSs were used to determine theinstrumental transmission of the spectrometer. Further checks of the relative shape ofthese DCS measurements were made using the method of gas mixtures (Ne mixedwith Ar). We also present results from new calculations of these DCSs using theR-matrix method, the unitarized first-order many-body theory, the semi-relativisticdistorted-wave Born approximation, and the relativistic distorted-wave method.Comparison with available experimental DCSs and DCS ratios is also presented.

2-methyl furan: An experimental study of the excited electronic levels by electron energy loss spectroscopy, vacuum ultraviolet photoabsorption, and photoelectron spectroscopy

The vacuum ultraviolet absorption spectrum of 2-methyl furan has been recorded between 5 eV (248 nm) and 9.91 eV (125 nm) and absolute photoabsorption cross sections measured. The electronic excited states of the molecule have also been probed using high resolution electron energy loss spectroscopy. Recorded under electric–dipole conditions, it has confirmed the magnitude of the photoabsorption cross section values and extended the optical oscillator strength values up to 12 eV. Measurements at several scattering angles have allowed the angular behavior of differential cross section ratios for some features in the 5–7.1 eV region to be measured, which in turn have helped in the assignments of electronic states to observed absorption bands. A high-resolution photoelectron spectrum was measured and allowed the two lowest ionization energies to be determined, these have been used in the identification of the related Rydberg states. Vibrational fine structure in the photoelectron spectrum has also been analyzed. The spectrum is dominated by intense π–π* transitions. Rydberg series associated with the first and second ionization energies have been identified. The effects of symmetry reduction induced on the furan ring by the methyl substitution are also discussed.

Inclusive V production cross sections from 920 GeV fixed target proton-nucleus collisions

Inclusive differential cross sections $d\sigma_{pA}/dx_F$ and $d\sigma_{pA}/dp_t^2$ for the production of K 0 S , $\Lambda$ , and $\bar{\Lambda}$ particles are measured at HERA in proton-induced reactions on C, Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to $\sqrt{s} = 41.6$ GeV in the proton-nucleon system. The ratios of differential cross sections $d\sigma_{pA}$ (K $^{0}_{S})/d\sigma_{pA}(\Lambda)$ and $d\sigma_{pA}(\bar{\Lambda})/d\sigma_{pA}(\Lambda)$ are measured to be $6.2\pm 0.5$ and $0.66\pm 0.07$ , respectively, for xF $\approx\!-0.06$ . No significant dependence upon the target material is observed. Within errors, the slopes of the transverse momentum distributions $d\sigma_{pA}/dp_t^2$ also show no significant dependence upon the target material. The dependence of the extrapolated total cross sections $\sigma_{pA}$ on the atomic mass A of the target material is discussed, and the deduced cross sections per nucleon $\sigma_{pN}$ are compared with results obtained at other energies.

Differential cross sections and cross-section ratios for the electron-impact excitation of the neon2p53sconfiguration

Electron-impact differential cross-section measurements for the excitation of the ${2p}^{5}3s$ configuration of Ne are reported. The Ne cross sections are obtained using experimental differential cross sections for the electron-impact excitation of the $n=2$ levels of atomic hydrogen [Khakoo et al., Phys. Rev. A 61, 012701-1 (1999)], and existing experimental helium differential cross-section measurements, as calibration standards. These calibration measurements were made using the method of gas mixtures (Ne and H followed by Ne and He), in which the gas beam profiles of the mixed gases are found to be the same within our experimental errors. We also present results from calculations of these differential cross sections using the R-matrix and unitarized first-order many-body theory, the distorted-wave Born approximation, and relativistic distorted-wave methods. Comparison with available experimental differential cross sections and differential cross-section ratios is also presented.

Why is theJ/ψsuppression enhanced at large transverse energy?

We study the ratio of differential cross sections $d\ensuremath{\sigma}{/dE}_{T}$ of $J/\ensuremath{\psi}$ to minimum bias event samples in Pb-Pb collisions at SPS energy. The NA50 data exhibit a sharp turnover at ${E}_{T}\ensuremath{\sim}100 \mathrm{GeV}$ (close to the knee of the ${E}_{T}$ distribution) followed by a steady, steep decrease at larger ${E}_{T}.$ We show that this behavior can be explained by the combined effects of a small decrease of the hadronic ${E}_{T}$ in the $J/\ensuremath{\psi}$ event sample (due to the ${E}_{T}$ taken by the $J/\ensuremath{\psi}$ trigger), together with a sharp decrease of the ${E}_{T}$ distributions in this ${E}_{T}$ region (tail). This phenomenon does not affect the (true) ratio of $J/\ensuremath{\psi}$ to DY differential cross sections (obtained by the NA50 standard analysis), but it does affect the one obtained by the so-called minimum-bias analysis. A good agreement is obtained with the data coming from both analysis---as well as with those on the ratios of $J/\ensuremath{\psi}$ and DY to minimum-bias differential cross sections -- in the whole ${E}_{T}$ region.

Measurement of the ratio of differential cross sections for W and Z boson production as a function of transverse momentum in p collisions at =1.8 TeV

We report on a measurement of the ratio of the differential cross sections for W and Z boson production as a function of transverse momentum in proton-antiproton collisions at sqrt(s) = 1.8 TeV. This measurement uses data recorded by the D0 detector at the Fermilab Tevatron in 1994-1995. It represents the first investigation of a proposal that ratios between W and Z observables can be calculated reliably using perturbative QCD, even when the individual observables are not. Using the ratio of differential cross sections reduces both experimental and theoretical uncertainties, and can therefore provide smaller overall uncertainties in the measured mass and width of the W boson than current methods used at hadron colliders.

Differential cross sections for electron-impact excitation of krypton at low incident energies: I. Excitation of the 4p55s configuration

The electron-impact excitation of the individual levels that constitute the 4p55s configuration of Kr is experimentally and theoretically investigatedat incident electron energies of 20.0, 15.0, 13.5 and 12.0 eV, for scatteringangles ranging from 10° to 135°. High resolutionelectron energy-lossspectroscopy is used to obtain spectral intensities for the excitation ofeach of the four 4p55s levels from the ground state. The intensitieslead to three differential cross section ratios. Absolute electron-impactexcitation cross sections are then determined by normalization to elasticscattering cross sections using the conventional inelastic to elasticnormalization method. The present theoretical cross sections are calculatedusing two different methods, namely the R-matrix method and theunitarizedfirst-order many-body theory. Comparisons between the experimental and thetheoretical results show some good agreement, but reveal areas wheresignificant improvement of the present models is needed. Additionally, it isshown that in the present case, just as in general for the rare gases,differential cross section ratios provide a sensitive test of theoreticalmodels as well as unique insights concerning relativistic effects in thescattering process. Comparisons with existing models and other experimentaldata are also presented.

Rayleigh to compton differential cross-section ratios in liquid xenon

Liquid xenon was irradiated with 662 keV γ-rays from a 137 Cs (7.4 GBq) source and spectra were obtained at angles from 3 to 25°. The xenon target was liquefied in a cryogenic chamber specially designed for this type of experiment. In situations in which it was possible to distinguish between the elastic and inelastic scattered photon peaks, the Rayleigh to Compton differential cross-section ratio was measured. Data on elastic and inelastic scattering were compared with theoretical predictions based on the S-matrix theory and on the incoherent scattering factor theory, respectively. The results show good agreement between calculated and experimental data for every measured angle. Effects related to liquid structure could not be seen in the measured momentum transfer range (1.4-11.5 A -1 ), being, if they exist, smaller than the experimental error.

Rayleigh to compton differential cross‐section ratios in liquid xenon

Liquid xenon was irradiated with 662 keV γ-rays from a 137Cs (7.4 GBq) source and spectra were obtained at angles from 3 to 25°. The xenon target was liquefied in a cryogenic chamber specially designed for this type of experiment. In situations in which it was possible to distinguish between the elastic and inelastic scattered photon peaks, the Rayleigh to Compton differential cross-section ratio was measured. Data on elastic and inelastic scattering were compared with theoretical predictions based on the S-matrix theory and on the incoherent scattering factor theory, respectively. The results show good agreement between calculated and experimental data for every measured angle. Effects related to liquid structure could not be seen in the measured momentum transfer range (1.4–11.5 Å−1), being, if they exist, smaller than the experimental error. Copyright © 1999 John Wiley & Sons, Ltd.

Measurement of the ratio of differential cross sections for double and single ionization of He by (4–10)-MeV protons

We have measured the ratio of differential cross sections for the production of doubly and singly ionized He by fast protons at energies between 4 and 10 MeV. The ratio was measured as a function of proton scattering angle, from which the energy transfer was calculated using binary kinematics. The ratio is found to be near 1.25{percent}, nearly independent of either proton energy or energy transfer. This value is lower than that reported previously for a similar experiment, but in good agreement with recent Compton scattering and theoretical results. {copyright} {ital 1998} {ital The American Physical Society}

Break-up and Coherent Photoproduction ofηMesons on the Deuteron

We present new break-up and coherent data for $\ensuremath{\eta}$ meson photoproduction on the deuteron, using a deuterium target and tagged bremsstrahlung photons up to 1 GeV. The differential cross sections for the coherent process were measured from threshold to 800 MeV. They are much smaller than those previously reported. The break-up channel provides a direct measurement of the neutron to proton differential cross section ratios. At the ${S}_{11}(1535)$ resonance peak, ${\ensuremath{\sigma}}_{n}/{\ensuremath{\sigma}}_{p}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.68\ifmmode\pm\else\textpm\fi{}0.06$ leading to an isoscalar to isovector amplitude ratio of ${A}_{s}{/A}_{\ensuremath{\upsilon}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.096\ifmmode\pm\else\textpm\fi{}0.02$.

Relative shape of the bremsstrahlung-photon energy spectrum from 7.0-keV electrons on Ag and Au.

We have measured the relative shape of the bremsstrahlung-photon energy spectrum from 7.0-keV electrons incident on Ag and Au targets; the targets are thick enough to stop the incident electrons, yet thin enough to transmit a substantial fraction of the radiated photons. Our results for the ratio of double differential cross sections for the bremsstrahlung-photon emission from Ag and Au at 90\ifmmode^\circ\else\textdegree\fi{} to the incident electron beam direction are found to yield excellent agreement with Pratt's theoretical prediction [Comments At. Mol. Phys. 10, 121 (1981); .ul2 Electron Bremsstrahlung \ifmmode\times\else\texttimes\fi{}80: Theory and Recent Developments, Proceedings of the International Conference on X-ray Processes and Inner Shell Ionization, Stirling, Scotland, 1980, edited by D. J. Fabian, H. Kleinpoppen, and L. M. Watson (Plenum, New York, 1981)] on the relative shape of the spectrum; however, the thick-target effect introduces a discrepancy between experiment and theory of about 20%. Also, the calculated absolute efficiency of the detector employed using the theoretical bremsstrahlung cross sections is found to agree with the normalization to the radioactive source within the uncertainty of about 20% in the target thickness.

Valence and Rydberg states of ethyl iodide by electron energy loss spectroscopy

The energy scheme of ethyl iodide has been studied by excitation of the valence and Rydberg states lying in the near UV and UV (3-10 eV) by electron impact and the angularly resolved electron energy loss spectroscopy. The lowest energy valence triplet states have been identified in the 3-5.5 eV region with a maximum of transition probability around 4.3 eV and at 4.78 eV respectively. Additional valence singlet and/or triplet states have been suggested to be located between 5 and 6 eV. For the Rydberg series, several electronic states contribute to the lowest energy terms of the Rydberg bands. The differential cross sections for the B, C and D Rydberg bands have been measured and confirm that each state within the electronic multiplet in each band has a differential cross section different from that of the other. In addition excitation of the A1 states is very likely responsible of a minimum in the D/C and D/B differential cross section ratios. In addition the first terms of two new nd series converging to each spin-orbit component of the ionic ground state have been reported. Vibrational levels of the E(1) states which are the most intense in pseudo-optical conditions have been partly resolved for the first member of the ns, np and nd series.

Electron scattering by atomic hydrogen: Elastic and inelastic phenomena at 13.9-200 eV.

A six-state coupled-channel optical potential for electron-atom scattering is applied to electron-hydrogen scattering at energies of 13.87, 16.46, 19.58, 35, 40, 54.4, 100, and 200 eV. The n=1, 2, and 3 channels are coupled explicitly, whereas the rest of the excited states of the atom including the continuum are taken into account via the ab initio complex nonlocal polarization potential. The differential and integrated cross sections, as well as the exchange asymmetries for n=1 and 2 channels, the total cross section, and the \ensuremath{\lambda}, R, and I parameters for the 2p excitation, are presented at each energy. The ratio of differential cross sections for n=1 to 2, and for 2s to 2p, and the 2s+2p differential cross sections are found to be in good agreement with experiment. There are still some discrepancies between experiment and theory for the 2p angular correlation parameters \ensuremath{\lambda}, R, and I.

Émission de rayonnement Lyman α dans les collisions H2 + H*(2s) aux énergies thermiques

The study made in Can. J. Phys. 68, 206 (1990) of the thermal-energy collision between H2 and metastable H*(2s), which could lead to the emission of Lyman α radiation, is reconsidered to take into account possible polarization effects. The total wave function of the system is expanded in terms of the molecular states of the intermediate complex [Formula: see text], which constitute the minimal basis of the four adiabatic states dissociating into H2 + H* (n = 2) where they are normally degenerate in energy. The results of the calculation show the existence, between three of those states, of average values of the separation distance R ([Formula: see text] atomic units) of long-range [Formula: see text] electronic interactions which depend on the geometric form of the [Formula: see text] molecule. From the molecular data the hypothesis of no longer considering H2 with H*(2s) as a rigid rotator is postulated and justified, after a purely quantum mechanical treatment of the radial equations, the mean ratio of the (oscillating) polarization angular differential cross sections to the elastic ones is found important [Formula: see text]. The inelastic phenomena are anticipated to be more marked in the ortho than in the para hydrogen at a low collision energy (75 meV).[Journal translation]

Measurements of differential cross-section ratios for single-nucleon transfer reaction pairs near A = 25

Differential cross sections for the (d, p), ( 3He, d), (α, t), and (α, 3He) reactions involving seventy-one residual states in 23Na, 25Mg, 25Al, and 27Al have been measured at a forward angle with incident energies of 17.5, 20.2, 34.8, and 34.8 MeV, respectively. The ratio of cross-section pairs involving formation of the same residual state is determined for forty-five cases where both the angular momentum transfer and single-particle spectroscopic strength have been previously established. These are compared to values calculated with conventional distorted-wave Born approximation analyses, and the utility of this technique for identifying some levels which are possible s- or p-wave resonances is demonstrated and discussed for states in the vicinity of proton thresholds. An application is made involving proton threshold states in 27Al.