Low-energy γp scattering and determination of proton polarizabilities

For the first time, an analysis of all experimental data on the differential cross section for elastic γp scattering at photon energies below 150 MeV is performed in order to determine the electric (α _p) and magnetic (β _p) polarizabilities of the proton. A fit to these data with two free parameters α p and β _p embedded into the theoretical cross section obtained on the basis of finite-energy s-channel dispersion relations gives the following world-average values of the proton polarizabilities: α _p=11.7±0.8 (stat.+syst.)±0.7 (model), β _p=2.3±0.9 (stat.+syst.)±0.7 (model) in units of 10^?4 fm³. The first error is combined—it takes into account the statistical and systematic errors in the experimental cross sections—while the second error comes from the theoretical uncertainties in the dispersion-theory cross sections.     

26g,mAl production cross sections from the 23Na(α, n)26Al reaction

Cross sections have been determined for the production of ^{26g, m}Al from the ²³Na(α, n) reaction. Total ²⁶Al production cross sections were obtained from measurements of the thick-target neutron yield. ^26mAl cross sections were measured using an activation technique. ^26gAl cross sections were deduced by subtracting the ^26mAl cross sections from the total (α, n) cross sections. The principle of detailed balance has been applied to the low-energy data to obtain cross sections for the astrophysically interesting ^26gAl(n, α₀)²³Na reaction. These results are compared with the results of Hauser-Feshbach calculations.     

16O, 24, 26Mg, 28Si, 32S, 40Ca(α, 12C) and multi-α-cluster transfer reactions

The (α, ¹²C) reaction has been studied on a variety of nuclei, A = 16 to 40, at E_α = 90.3 MeV. The data indicate a rapid fall-off of cross sections with increasing target mass, approximately as A_t^{?5 ± 1}. This and other systematics are used to estimate cross sections for multi-α-cluster transfer reactions in heavy nuclei and suggest σ_T < 10^?34 cm² consistent with present experimental limits. The data for ²⁴Mg(α, ¹²C)¹⁶O has been studied in more detail and indicates a selective population of final states including ¹⁶O g.s., with oscillatory angular distributions in some instances. Finite-range distorted-wave Born approximation calculations for direct ⁸Be pickup have been performed utilizing cluster overlap amplitudes obtained with zero-order SU(3) wave functions. The calculations are in qualitative, and often quantitative, agreement with shapes and absolute magnitudes of the measured angular distributions although the cross sections for certain α-cluster states (2⁺, E_x ≈ 7 MeV; 4⁺, E_x ≈ 10.3 MeV) are greatly overestimated with this model. Other more complicated mechanisms, such as successive α-transfer, cannot be excluded. The systematics of the calculated ⁸Be cluster overlaps and the calculated and measured (α, ¹²C) cross sections are investigated, and implications for multi-α-cluster transfer reactions are discussed.     

Bremsstrahlung in proton-α scattering

Proton-α bremsstrahlung cross sections have been measured at 45 MeV for θ_p = 91°, θ_α = 30° and θ_p = 70°, θ_α = 39°; at 40 MeV for θ_p = 92°, θ_α = 29°; and at 22 MeV for θ_p = 70°, θ_α = 30°. Calculations for these cross sections have been made using the Feshbach-Yennie model following the methods of Green and Prodon including p-α partial waves up to L = 4. These potential-independent calculations have only the proton-α elastic-scattering phase shifts as input. Good agreement with the experimental cross sectios has been obtained.     

Perturbative QCD calculation of jet cross sections in e+e− annihilation

We calculate the α_s² to three-jet cross sections in e⁺e^? annihilation in a scheme that uses regulator masses for the infrared and collinear divergences. Using various methods to define the three-jet region, we find that the corrections to the O(α_s) cross sections are large.     

Comparison of π±, K± and p,p production in the central rapidity region in hadron-hadron collisions and in e+e− annihilation

We compare the p_T dependence of pion, kaon and proton production cross sections in the central rapidity region in e⁺e⁻ annihilation events and in proton-proton collisions at ISR energies. We find similarities both in the p_T dependence of cross sections and in the particle composition as a function of p_T, in agreement with the hypothesis of a universal mechanism of particle production.     

Theoretical study of photoionization of the isoelectronic sequence Rb<Superscript>+</Superscript>, Sr<Superscript>2+</Superscript>, and Y<Superscript>3+</Superscript>

The photoionization cross sections for the 4p shell of ions of the Kr isoelectronic sequence Rb⁺, Sr²⁺, and Y³⁺ are calculated. The configuration interaction theory and the perturbation theory are used to describe the many-electron effects. The relativistic effects are taken into account in the Pauli-Fock approximation. The calculated resonance structure of photoionization cross sections for the 4p shell in the region below the 4s threshold associated with the autoionization of the 4s-np singly excited states and the 4p4p-nln′l′ doubly excited states reproduces the results of recent measurements of total photoabsorption cross sections for the Rb⁺, Sr²⁺, and Y³⁺ ions. It is found that, as the nuclear charge in the isoelectronic sequence increases, the ratio between the direct and correlation parts of amplitudes of the 4s-(n/?)p transition changes and, as the consequence, the minimum of the photoionization cross section of the 4s shell shifts from the continuous spectrum to the region of states of discrete spectrum. This accounts for the strong changes in the shape of the 4s-np resonances in the photoionization cross sections for the 4p shell of Rb⁺, Sr²⁺, and Y³⁺, as well as the distinction between the shapes of the 4s-6p _1/2 mirror resonance in the partial 4p _1/2 and 4p _3/2 photoionization cross sections for the Y³⁺ ion which do not suppress each other in the total photoionization cross section, as is the case for similar resonances in Rb⁺ and Sr²⁺.     

The (γ, p0) reactions in the giant dipole resonance region of 51V and 52Cr nuclei

The differential cross sections at 90° for the ⁵¹V(e, p₀)⁵⁰Ti and ⁵²Cr(e, p₀ + p₁)⁵¹V reactions have been measured over the giant dipole resonance region. These cross sections were used to obtain the differential cross sections of the ⁵¹V(γ, p₀)⁵⁰Ti and ⁵²Cr(γ, p₀ + p₁)⁵¹V reactions. The results show two peaks that appear at the same energies as the main peaks of the (γ, n) and (γ, p) cross section for both nuclei. The angular distributions of protons from the (e, p) reaction have also been measured at several points of the incident electron energy. The coefficients A₂ obtained by fitting with a series of Legendre polynomials, W(θ) = 1 + A₁P₁(cos θ)+A₂P₂(cos θ), varies with excitation energy. These results are discussed in terms of the direct-semidirect process considering isospin effects in the giant dipole resonance.     

Inner-shell ionization ofZ=25–32 elements by 5-48 MeV32S ions

TheK-shell ionization cross sections of Mn, Ni, Cu, Zn and Ge under³²S bombardment have been measured in the energy range from 5 to 48 MeV. The cross sections are compared with available theories based on a direct Coulomb ionization mechanism and with the predictions of theK-vacancy sharing process. This last process can reasonably account for the measured cross sections at high bombarding energies. The energy shifts of theK _α- andK _β-lines and theK _α/K _β-intensity ratios have also been measured. This information is used to deduce the defect configuration of the atoms. The mechanisms responsible for the multiple vacancy production are discussed.     

Elastic and inelastic scattering of 800-MeV protons on <Superscript>16</Superscript>O and <Superscript>20</Superscript>Ne nuclei

Differential cross sections and polarization observables for the elastic and inelastic scattering of 800-MeV protons on ¹⁶O and ²⁰Ne nuclei are calculated on the basis of the theory of multiple diffractive scattering and the α-cluster model involving dispersion. The single-particle nucleon-density distributions obtained within the α-cluster model involving dispersion are used in the calculations. The differential cross sections and polarization calculated for elastic and inelastic p¹⁶O and p²⁰Ne scattering are compatible with available experimental data. The spin-rotation functions calculated for elastic p¹⁶O and p²⁰Ne scattering within the independent-nucleon model differ qualitatively from their counterparts calculated within the α-cluster model involving dispersion.     

Ξ− and Ξ− inclusive production in Ξ− Be interactions at 116 GeV/c

The cross sections for Ξ^? and Ω^? inclusive production in Ξ^? Be collisions at 116 GeV/c have been measured in the kinematic domain [0.1<x _F <0.9, 0<p _T <1.7 GeV/c]. The integrated cross sections per nucleon are found to be about twice as large as in Ξ^? p collisions. The invariant cross sections increase by a factor of 70 for the Ξ^? s and of 100 for the Ω^? s between the central region (x _F ～0.2) and the projectile fragmentation region (x _F ～0.8). In the central region, they have about the same magnitude as the ones for Ξ^? and Ω^? inclusive production inp nucleon collisions. The Ξ^? and Ω^? polarisations have been measured over the same kinematic domain and are found to be compatible with zero.     

Charged-particle decay of 28Si induced by quasi-monochromatic annihilation photons in the GDR

Spectra of protons and alpha-particles, emitted from the giant electric dipole resonance of ²⁸Si excited by quasi-monochromatic photons from in-flight annihilation of accelerated positrons, were measured. Cross sections for six charged-particle decay channels were extracted in the energy region from 16.8 to 25.7 MeV. While the (γ, α₀) cross section is completely statistical in nature, the (γ, p) process was found to have a 65% semidirect component, mainly in the (γ, p₀) and (γ, p₁₊₂) channels.     

A measurement of the KL0p elastic cross section for 3 ⩽p⩽13 GeV/c and 0.1⩽|t|⩽1.3 GeV2

The cross section for the K_L⁰p elastic scattering has been measured for the first time. The incident momentum and momentum transfer ranges are 3 ?p? 13 GeV/c, 0.1 ? |t| ? 1.3 GeV². The results are compared to those of other experiments related to ours by isotopic spin conservation, finding agreement with some and discrepancies with others. The differential cross sections have been parametrized in the form Ae^bt. The coefficients show little or no dependence on energy, with A ? 9.8 mb · GeV^?2and b ? 4.7 GeV^?2. The effective linear trajectory has been determined and gives α₀ = 0.95 ± 0.15, α′ = ?0.35 ± 0.48 GeV^?2, in good agreement with dominance by pomeron exchange.     

Inclusive π 0 and KS 0 production in two-photon collisions at LEP

The reactions e⁺e⁻→e⁺e⁻ π ⁰ X and e⁺e⁻→e⁺e⁻K_S ⁰ X are studied using data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV. Inclusive differential cross sections are measured as a function of the particle transverse momentum p _t and the pseudo-rapidity. For p _t ⩽1.5 GeV, the π ⁰ and K_S ⁰ differential cross sections are described by an exponential, typical of soft hadronic processes. For p _t ⩾1.5 GeV, the cross sections show the presence of perturbative QCD processes, described by a power-law. The data are compared to Monte Carlo predictions and to NLO QCD calculations.     

Measurements ofK-shell ionization with132Xe and208Pb projectiles in the energy range of 1.4–5.9 MeV/u

Projectile and targetK-shell ionization cross sections induced by 3.6-, 4.7-, and 5.9 MeV/u¹³²Xe ions and 1.4-, 3.6-, 4.7-, and 5.9 MeV/u²⁰⁸Pb ions from the UNILAC in thin solid targets between C and U are measured. The cross sections are discussed in terms of the molecular model of innershell vacancy production in heavy ion-atom collisions. The sharing of 2p _1/2σ vacancies between theK shells of the two collision partners in these very heavy ion-atom collisions is found to deviate from the Meyerhof-Demkov formula forR≦10^?2. The measured ionization cross sections are compared with theoretical calculations for 1sσ and 2p _1/2σ excitation cross sections. AZ _UA=Z₁+Z ₂ dependence is found independent ofZ ₁/Z ₂. Outer-shell vacancy configurations measured in these close encounters are reported.     

Excitation of Jπ=2+ resonances in 24Mg by the 23Na(p, 12C)12C reaction

Angular distributions of the ²³Na(p, ¹²C_g.s.)¹²C_g.s. reaction were measured at energies on top of resonance-like structures or close to them in the range E_p=8−18 MeV and were analysed using parametrized S-matrix elements. Partial cross sections proceeding through compound nuclear states of ²⁴Mg with various spin J were derived. In was found that the resulting cross sections for J=2 exhibit correlated structures with the “fissioning resonances” recently observed by the ¹²C(¹²C, λ₀) and ²⁴Mg(α, α') ¹²C_g.s + ¹²C_g.s. reactions.     

Angular distributions of neutron polarization from the 14C(p,n)14N and 11B(α, n)14N reactions and R-matrix analysis oF 15N in the excitation-energy range between 11.5 and 12.5 MeV

Angular distributions of neutron polarization from the ¹⁴C(p, n)¹⁴N and ¹¹B(α, n)¹⁴N reactions have been studied for the particle energies E_p = 1.788, 2.025, 2.272 and 2.450 MeV, and E_α = 2.049 MeV. The polarization was derived from the left-right asymmetry induced by elastic scattering from ⁴He. Together with existing measurements of angular distributions and total cross sections for several reaction channels leading to ¹⁵N with an excitation energy between 11.5 and 12.5 MeV, these data were used to deduce from R-matrix analysis a set of resonance parameters for the ¹⁵N levels in this energy range.     

K-vacancy production by 3.6-, 4.75-, and 5.9-MeV/amu238U Ions

Projectile (Z ₁) and target (Z ₂)K-vacancy production cross sections induced by 3.6-, 4.75-, and 5.9-MeV/amu²³⁸U ions in selected targets between C and U are reported. The cross sections are discussed within the context of the molecular model of inner-shell vacancy production in heavy-ion-atom collisions. The measured 1sσ and 2pσ excitation cross sections are compared with semiempirical formulas, and with the perturbed-stationary-states calculations of Betz et al. The dependence of these cross sections onZ _u =Z₁+Z ₂ agrees well with the Betz calculations. However, the measured cross sections are factors of 2 to 4 (1sσ) and 4 to 5 (2pσ) larger than the theoretical values.     

Lepton pair production at large transverse momentum in second order QCD

The production of Drell-Yan pairs at large transverse momentum is calculated up to O(α_s²) for a non-singlet combination defined as the cross section for an incident particle minus the analogous cross section for an incident antiparticle. Analytic results are presented for all cross sections and numerical estimates are given at various energies of experimental interest.     

Measurements of the (γ, n0) reaction on 12C and 16O and the investigation of the reaction mechanism

Differential (γ, n₀) cross sections on ¹²C and ¹⁶O have been measured for photon energies 60 MeV ? E_γ ? 160 MeV. These results combined with the corresponding (γ, p₀) cross sections support an absorption mechanism of the photon by neutron-proton pairs.