Oscillatory screening and quantum interference effects on electron collisions in quantum plasmas

The oscillatory screening and collision-induced quantum interference effects on electron-electron collisions are investigated in dense quantum plasmas. The modified Debye-Hückel potential with the total spin states of the system is considered to obtain the differential electron-electron scattering cross section in quantum plasmas. It is shown that the electron-electron scattering cross section decreases with an increase of the quantum wave number. In addition, the minimum position of the cross section has been appeared with increasing the collision energy at the scattering angle θL=π/4. It is also found that the oscillatory screening effects strongly suppress the cross section near θL=π/4. In addition, it is found that the quantum interference effects suppress the cross section, especially, for the forward and backward scattering cases.     

Inelastic interactions of fast nucleons with nuclei and fission of nuclei

The cross section for the fission of actinide nuclei that is induced by fast neutrons is considered as a fraction of the cross section for inelastic nucleon interaction with nuclei. In turn, inelastic nucleon interaction with a nucleus is treated as scattering on intranuclear nucleons. It is shown that this interaction model describes satisfactorily the cross section for the inelastic interaction of 60- to 2200-MeV nucleons for a broad set of nuclei and that the energy dependence of the cross section for the fission of actinide nuclei that is induced by 400- to 1000–MeV protons replicates the energy dependence of the cross section for inelastic interactions with respective nuclei. From the model used, it follows that the cross sections for proton-nucleus interactions exceed cross sections for respective neutron-nucleus interactions in the energy range extending up to 550 MeV; at higher energies neutron cross sections are larger than proton cross sections.     

New physics, the cosmic ray spectrum knee, and pp cross section measurements

We explore the possibility that a new-physics interaction can provide an explanation for the knee just above 10⁶ GeV in the cosmic ray spectrum. We model the new-physics modifications to the total proton–proton cross section with an incoherent term that allows for missing energy above the scale of new physics. We add the constraint that the new physics must also be consistent with published pp cross section measurements, using cosmic ray observations, an order of magnitude and more above the knee. We find that the rise in cross section required at energies above the knee is radical. The increase in cross section suggests that it may be more appropriate to treat the scattering process in the black disc limit at such high energies. In this case there may be no clean separation between the standard model and new-physics contributions to the total cross section. We model the missing energy in this limit and find a good fit to the Tibet III cosmic ray flux data. We comment on testing the new-physics proposal for the cosmic ray knee at the Large Hadron Collider.     

Comparative analysis of characteristic electron energy loss spectra and inelastic scattering cross-section spectra of Fe

The inelastic electron scattering cross section spectra of Fe have been calculated based on experimental spectra of characteristic reflection electron energy loss as dependences of the product of the inelastic mean free path by the differential inelastic electron scattering cross section on the electron energy loss. It has been shown that the inelastic electron scattering cross-section spectra have certain advantages over the electron energy loss spectra in the analysis of the interaction of electrons with substance. The peaks of energy loss in the spectra of characteristic electron energy loss and inelastic electron scattering cross sections have been determined from the integral and differential spectra. It has been shown that the energy of the bulk plasmon is practically independent of the energy of primary electrons in the characteristic electron energy loss spectra and monotonically increases with increasing energy of primary electrons in the inelastic electron scattering cross-section spectra. The variation in the maximum energy of the inelastic electron scattering cross-section spectra is caused by the redistribution of intensities over the peaks of losses due to various excitations. The inelastic electron scattering cross-section spectra have been analyzed using the decomposition of the spectra into peaks of the energy loss. This method has been used for the quantitative estimation of the contributions from different energy loss processes to the inelastic electron scattering cross-section spectra of Fe and for the determination of the nature of the energy loss peaks.     

Influence of quark energy loss on extracting nuclear sea quark distribution from nuclear Drell-Yan experimental data

By means of two typical kinds of quark energy loss parametrization and the nuclear parton distribu-tions determined only with lepton-nuclear deep inelastic scattering experimental data, a leading order analysis is performed on the proton-induced Drell-Yau differential cross section ratios of tungsten versus deuterium as a function of the quark momentum fraction in the beam proton and target nuclei. It is found that the theoretical results with quark energy loss are in good agreement with the experimental data. The quark energy loss effect produces approximately 3% to 11% suppression on the Drell-Yan differential cross section ratios RW/D in the range 0.05 ≤ x2≤ 0.3. The application of nuclear Drell-Yan data with heavy targets is remarkably subject to difficulty in the constraint of the nuclear sea quark distribution.     

Semi-hard parton rescatterings in nuclear collisions at very high energies

Representing the semi-hard partonic interactions by the exchange of Lipatov's perturbative Pomeron, we express the semi-hard nuclear cross section as a self shadowing cross section. With the help of a generating functional technique, we obtain average numbers of multiple semi-hard partonic collisions without any need of using explicit expressions for the multi-parton distributions. The average number of semi-hard interactions of a given projectile parton against a target nucleus is estimated quantitatively and it is shown to grow very rapidly above one with increasing the c.m. energy.     

Effect of electric field on photoproduction of electron-positron pairs

The cross section of electron-positron pair production by two circularly polarized photons in a static uniform electric field is calculated. The dependence of the cross section on the photon energy is determined. It is shown that the corrections to the cross section of the process involving photons of various polarizations are suppressed as compared to the situation with crossed fields.     

Collision of Bare Ion Si~(14+) with the Same Z Slow-atom Si

We present the collision of bare ion Si 14+ with the same Z slow atom Si. It is shown that the cold-atom collisions are sensitive to the potential. In this paper, we present the cross sectiond for the most important transition from the 3p 13d 1 and 3p 14d 1 excited states. It is seen that there are large cross sections when the angle is larger than 80 degrees. With increasing energy, the cross section becomes decresasingly flat. PACS numbers: 34.70.+e, 32.80. Fb     

Polarization bremsstrahlung process in quantum plasmas including electron-exchange and shielding effects

The electron-exchange and quantum shielding effects on the polarization bremsstrahlung spectrum due to the electron-shielding sphere encounters are investigated in quantum plasmas. From this work, it is found that the electron-exchange effect strongly suppresses the polarization bremsstrahlung radiation cross section. Additionally, it is found that the polarization bremsstrahlung radiation cross section increases with increasing plasmon energy and, however, decreases with increasing Fermi energy. The variation of the influence of electron-exchange and quantum shielding on the polarization bremsstrahlung spectrum is also discussed.     

Collision of Bare Ion Si~(14 ) with the Same Z Slow-atom Si

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Correlations between transverse energy production and the Drell-Yan process in heavy ion collisions at high energy

The expression for the Drell-Yan cross section is presented which takes into account the geometry of heavy ion collisions. The Drell-Yan cross section is shown to be proportional to the transverse energy produced within a fixed rapidity interval. A dependence steeper than linear of the cross section for production of dileptons with masses larger than about 2 GeV on the transverse energy in a given rapidity bin would be a clear-cut signal for the formation of the quark-gluon plasma.     

Rising Inelastic Cross Section and its Contribution to Steepening of the Cosmic Ray Energy Spectrum

Calculations have been carried out to investigate the contribution of an increasing total cross section to steepening of the cosmic ray energy spectrum at very high energies (E ? 10¹² eV). Our results suggest that increasing total cross section contributes only a part to the steepening of primary energy spectrum at very high energies even if the composition is pure primary iron flux.     

Influence of the Coulomb interaction in the final state on the cross section of single-electron capture by fast ions

It is shown that the Coulomb interaction of ions in the final state must be taken into account in the estimation of the cross section of electron capture by fast ions. The cross section of electron capture decreases considerably, and the dependence of the cross section on the collision energy becomes close to the experimental one if the interaction of charged particles after collision is taken into account.     

s Wave resonances with square well potentials

The three dimensional square well potential is discussed. It is shown that there are no observable resonances in the cross section except for the zero energy resonance. This is remarkable because almost every textbook on the topic discusses a series of regularly spaceds wave resonances. The lack of non-zero energy resonances in thes wave cross section of the square well potential cannot, however, be generalized to other purely attractive potentials. This is shown with a specific example.     

The reaction mechanism of heavy ion scattering at intermediate energies

The contribution to the real and imaginary nucleus-nucleus (N-N) optical potential from nucleon-nucleon scattering in the medium is calculated in a local density approximation from a two Fermi sphere nuclear matter picture for the N-N collision. This reaction mechanism is shown to be dominant for ¹²C + ¹²C scattering at all considered energies (160 MeV < E_lab < 2250 MeV) giving a weakly energy dependent reaction cross section of about 900 mb. Inclusion of the collective 2⁺, 3^? excitations in a coupled channel calculations gives good agreement for both the measured elastic and inelastic 2⁺ cross section at E_lab = 1016 MeV. This fully microscopic parameter free calculation indicates that the energy dependence of the reaction cross section for this system is mostly due to the decrease of the collective contribution with increasing energy contrary to current theoretical models.     

Nonuniform charge distribution effects on bremsstrahlung emission in drifting dusty plasmas

The effect of the nonuniform charge distribution due to the ion flow on the ion–dust grain bremsstrahlung process is investigated in dusty plasmas. The impact-parameter analysis is applied to the motion of the projectile ion in order to investigate the variation of the bremsstrahlung radiation cross section as a function of the impact parameter, Debye length, Mach number, radiation photon energy, and projectile energy. The result shows that the nonuniform charge distribution effect strongly enhances the bremsstrahlung cross section. It is also found that the bremsstrahlung radiation cross section decreases with increasing the Debye length.     

Influence of then-n cross section on the observables in dynamical process of heavy ion collisions

The influence of then- n cross section on the observables in dynamical process of heavy ion collisions was investigated by means of the BUU (Boltzmann-Uehling-Uhlenbeck) equation. The influence of then-n cross section upon transverse momentum, flow angle and quadrupole moment of momentum distribution with increasing incident energy was successfully illustrated according to the variation law ofn-n cross section with and without the medium effects with increasing bombarding energy. This investigation also shows a close relationship between the medium effects of then- n cross section and the nuclear equation of state (EOS).     

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.     

A New Qualitative Prediction of the Parton Model for High-Energy Hadron Collisions

Inclusive single jet production in hadron collisions is considered. It is shown that the QCD parton model predicts a nonmonotonic dependence of the inclusive cross section on the fraction of the energy deposited in the jet registered, if it is normalized on the same cross section measured at another collision energy. Specifically, if the cross section is normalized by the one measured at a higher collision energy, it possesses a minimum which depends on jet rapidity. This prediction can be tested at the Fermilab Tevatron, at the CERN LHC, and at the Very Large Hadron Collider under discussion.     

一种考虑几何屏蔽效应的计算“电子-分子”散射总截面的可加性规则修正方法

在考虑分子内原子间的几何屏蔽效应随电子入射能量变化的基础上, 提出了一种能够在中、高能区准确计算“电子-分子”散射总截面的可加性规则修正方法. 利用这一修正后的可加性规则并使用“电子-C, H, O, N原子”散射总截面的实验数据, 在50—5000 eV内计算了电子被NO, N₂O, NO₂和C₂H₆分子散射的总截面, 且将计算结果与实验结果及其他理论结果进行了比较. 结果表明, 利用这一方法修正过的可加性规则进行计 关键词： 电子散射 可加性规则 总截面 几何屏蔽效应