Scattering and absorption differential cross sections for double photon Compton scattering

The scattering and absorption differential cross sections for nonlinear QED process such as double photon Compton scattering have been measured as a function of independent final photon energy. The incident gamma photons are of 0.662 MeV in energy as produced by an 8 Ci¹³⁷Cs radioactive source and thin aluminum foils are used as scatterer. The two simultaneously emitted photons in this process are detected in coincidence using two Nal(T1) scintillation detectors and a slow-fast coincidence set-up of 30 nsec resolving time. The measured values of scattering and absorption differential cross sections agree with theory within experimental estimated error.     

IR-improved DGLAP-CS theory: Kernels, parton distributions, reduced cross sections

It is shown that exact, amplitude-based resummation allows IR-improvement of the usual DGLAP-CS theory. This results in a new set of kernels, parton distributions and attendant reduced cross sections, so that the QCD perturbative result for the respective hadron-hadron or lepton-hadron cross section is unchanged order-by-order in α_s at large squared-momentum transfers. We compare these new objects with their usual counter-parts and illustrate the effects of the IR-improvement in some phenomenological cases of interest with an eye toward precision applications in LHC physics scenarios.     

An atomic diffraction theory of molecular photoionization cross sections

A theory of molecular photoionization cross sections is developed on the basis of locally atomic character of the one-electron final state in the Golden Rule expression for the molecular orbital cross section. Ionization amplitudes from several atomic centres are added and rotationally averaged to produce molecular orbital cross sections displaying a sum of pseudo-atomic cross sections weighted according to the LCAO composition of the orbital and also two-centre products reflecting interference effects. The atomic ionization amplitudes are obtained by use of an atomic central potential constructed by an inversion procedure from the form of the ground state orbital. The theory is of a simple chemical nature but usually of at least semi-quantitative accuracy. In this work we illustrate the nature of the two-centre interference effects in small diatomic molecules (H₂, HF, N₂).     

On the calculation of scattering cross sections from absorption cross sections

A dispersion-type relation between photon scattering and absorption cross sections is derived. It is shown that the relation gives the correct scattering cross section in the low and high frequency limits, and is consistent with the Kramers-Heisenberg formula in the vicinity of a resonance. The practical application of the relation is illustrated by calculations of the scattering cross section and refractive index of He and Ne at STP and dry air at 1200°K from known absorption cross section data. The method is useful for obtaining scattering cross sections, polarizabilities, and refractive indices at elevated temperatures.     

Comparison of high energy neutron-nucleus total cross sections with theory

A recent paper by Julius purports to show that previous estimates of the effect of inelastic screening on neutron-nucleus total cross sections are much too large. However, we show that most of this discrepancy is due to his uections for diffractive N¹ production which are much too small. The rest may be due to the assumptions in his model. We also emphasize that experimental support for the inelastic screening corrections does not rely on a specific choice of nuclear radii.     

计算中低能量电子与水分子弹性散射微分截面

运用耦合通道光学势方法计算了在中低能量下的电子与水分子碰撞弹性散射微分截面,其中靶的极化效应被包含在一个从头算的等价局域势中.随后将计算结果与实验值和其它理论计算结果进行了比较.结果显示这种计算方法对于电子与极化分子体系碰撞是非常适用的.     

Geometric scaling,multiplicity distributions and cross sections

From a geometric picture of hadrons as extended objects we arrive at some universal features of high energy collisions. In this approach the mean multiplicity, as a function of s, and the KNO scaling function are universal, and asymptotically the ratio σ_elastic/σ_total is expected to be the same for all processes.     

The total charge-changing cross sections and the partial cross sections of 56Fe fragmentation on Al,C and CH2 targets

The total charge-changing cross sections and the partial cross sections of ⁵⁶Fe fragmentation on polyethylene, carbon and aluminum targets at the highest energy of 496 A MeV are investigated using CR-39 plastic nuclear track detector. The total charge-changing cross-section for hydrogen target is calculated based on the results of polyethylene and carbon targets. It is found that the total charge-changing cross sections for fragmentation of ⁵⁶Fe on hydrogen, carbon and aluminum targets are independent on the beam energy in our studied energies, and are consistent with the predictions of Bradt–Peter semi-empirical formula, Nilsen parameterized formula, NUCFRG2 and QMSFRG theoretical simulation codes. The partial cross sections for projectile fragment production are independent on beam energy in our studied energies for each targets and do not show a significant even-odd effect.     

用反应窗理论研究离子与原子碰撞的态选择微分截面

基于描述低能离子与原子碰撞的分子库仑过垒模型,详细阐述了与入射离子速度相关的反应窗理论,并对影响势垒变化的平均径向速度做了修正.根据该理论,计算了C5 -He和He2 -He碰撞体系单电子俘获过程的态选择微分截面,并分别与Kamber等人和Mergel等人的实验结果进行了比较.     

Defect of total nuclear scattering cross sections: Fifty years of the Glauber diffraction theory

In this mini survey, a historical excursus into theoretical investigations on the diffraction theory of fundamental nuclear processes, the origins of which go back to work by Glauber (1955), is presented with an emphasis on recent achievements in the field.     

Electron excitation cross sections of Li,Na and K

The Vainshtein approximation with exchange via the Ochkur-Rudge method and Ochkur's modified first Born approximation are used to calculate electron excitation cross sections of Li, Na and K. The results are compared with experiments and the frozen core Glauber cross sections.     

Increasing p-p and p-nucleus cross sections

p-Nucleus cross sections are calculated assuming that total p-p cross sections increase with energy. The dependence on the nucleon structure in b-space is examined and it is found that p-nucleus cross sections grow very rapidly with A if the increasing p-p cross section is attributed to an expanding nucleon halo.     

Optimized perturbation theory applied to jet cross sections ine + e − annihilation

The optimized perturbation theory proposed by Stevenson to deal with coupling constant scheme dependence is applied to the calculation ofπ _tot and jet multiplicities ine ⁺ e ^? annihilation. The results are compared with those of simple perturbation theory and with recent experimental cluster multiplicities.