Photoionization of the outer electrons in noble gas endohedral atoms

We suggest a prominent modification of the outer shell photoionization cross section in noble gas (NG) endohedral atoms NG@C _n under the action of the electron shell of fullerene C _n . This shell leads to two important effects: a strong enhancement of the cross section due to fullerene shell polarization under the action of the incoming electromagnetic wave and to prominent oscillation of this cross section due to the reflection of a photoelectron from the NG by the fullerene shell. Both factors lead to powerful maxima in the outer shell ionization cross sections of NG@C _n , which we call giant endohedral resonances. The oscillator strength reaches a very large value in the atomic scale, 25. We consider atoms of all noble gases except He. The polarization of the fullerene shell is expressed in terms of the total photoabsorption cross section of the fullerene. The photoelectron reflection is taken into account in the framework of the so-called bubble potential, which is a spherical δ-type potential. It is assumed in the derivations that the NG is centrally located in the fullerene. It is also assumed, in accordance with the existing experimental data, that the fullerene radius R _C is much larger than the atomic radius r _A and the thickness Δ_C of the fullerene shell. As was demonstrated recently, these assumptions allow us to represent the NG@C _n photoionization cross section as a product of the NG cross section and two well-defined calculated factors. The text was submitted by the authors in English.     

D meson production in deep-inelastic diffractive interactions at HERA

A measurement is presented of the cross section for D^*± meson production in diffractive deep-inelastic scattering for the first time at HERA. The cross section is given for the process ep→eXY, where the system X contains at least one D^*± meson and is separated by a large rapidity gap from a low mass proton remnant system Y. The cross section is presented in the diffractive deep-inelastic region defined by 2<Q²<100 GeV², 0.05<y<0.7, , M_Y<1.6 GeV and |t|<1 GeV². The D^*± mesons are restricted to the range p_T,D^*>2 GeV and |η_D^*|<1.5. The cross section is found to be 246±54±56 pb and forms about 6% of the corresponding inclusive D^*± cross section. The cross section is presented as a function of various kinematic variables, including which is an estimate of the fraction of the momentum of the diffractive exchange carried by the parton entering the hard-subprocess. The data show a large component of the cross section at low where the contribution of the boson–gluon-fusion process is expected to dominate. The data are compared with several QCD-based calculations.     

Total ionisation cross sections for chlorofluoromethanes and CClx radicals by electron impact

We report here the total ionisation cross section for chlorofluoromethanes, namely CCl₃F (Freon 11), CCl₂F₂ (Freon 12), CClF₃ (Freon 13), CHCl₂F (Freon 21), CHClF₂ (Freon 22), CH₂ClF (Freon 31), CCl₄ and CCl_x (x = 1–3), radicals by electron impact from ionisation threshold to 2 keV. The total inelastic cross section is obtained employing a complex optical potential formalism and solving the Schrödinger equation through partial wave analysis. Using the complex scattering potential-ionisation contribution method, the total ionisation cross section is derived from the inelastic cross section for these targets. The results obtained are then compared with the existing experimental and theoretical data, wherever available. The present result shows reasonable agreement with previous data. For the CCl_x radicals, the ionisation cross section is predicted for the first time. The data reported here have immense interest to atmospheric and technological plasma modelling.     

Three-body calculation of neutron-deuteron elastic scattering in the energy region from 2.5 MeV up to 50 MeV

The three-body Faddeev equations for neutron-deuteron scattering are solved in the energy region from 2.5 MeV to 50 MeV of the incident neutron energy with small energy steps. Higher-rank separable potentials are used in the¹ s ₀ wave and in the³ s ₁—³ d ₁ waves, while rank-1 separable potentials are used in¹ p ₁,³ p _0,1,2 ¹ d ₂ ³ d _2,3 waves. The calculation is compared with experiments for the total cross section, the total break-up cross section, the differential cross section and the analyzing power of neutron-deuteron scattering. The improvements in the agreement as compared to previous calculations are impressive in many cases. Especially, the calculated total cross section agrees with the experiment below 30 MeV within the error bars, which are as small as 1%. A discussion on the numerical accuracy is given. General aspects of the calculated cross section are discussed. It is pointed out that thes-wave asymptotic normalization of the deuteron wave function (A _s ) is important.     

Absorption of massless scalar wave from Schwarzschild black hole surrounded by quintessence

By using the partial wave method, we investigate the absorption of massless scalar wave from Schwarzschild black hole surrounded by the quintessence. We obtained the expression of absorption cross section
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Then we numerically carry out the absorption cross section and we find that the larger angular momentum quantum number l is, the smaller the corresponding maximum value of partial absorption cross section is, and that the total absorption cross section tends to geometric-optical limit σ_abs^hf≈ π b_c². We also find that higher value of ω_q (state parameter of the quintessence) corresponds the higher value of absorption cross section σ_abs.     

Giant resonances of endohedral atoms

It is demonstrated for the first time that the effect of a fullerene shell on the photoionization of a “caged” atom in an endohedral can result in the formation of giant endohedral resonances or GER. This is illustrated by the concrete case of the Xe@C₆₀ photoionization cross section that, at 17 eV, exhibits a powerful resonance with total oscillator strengths of about 25. The prominent modification of the 5p ⁶ electron photoionization cross section of Xe@C₆₀ takes place due to the strong fullerene shell polarization under the action of the incoming electromagnetic wave and the oscillation of this cross section due to the reflection of the photoelectron from Xe by the C₆₀. These two factors transform the smoothly decreasing 5p ⁶ cross section of Xe into a rather complex curve with a powerful maximum for Xe@C₆₀, with the oscillator strength of it being equal to 25. We also present the results for the dipole angular anisotropy parameter that is strongly affected by the reflection of the photoelectron waves, but not modified by C₆₀ polarization. The text was submitted by the authors in English.     

Complex scattering potential – ionization contribution (CSP-ic) method for calculating total ionization cross sections on electron impact

In this article, we report calculations of total ionization cross sections, Q _ion , for simple atoms (C, N, O, F) and molecules (NO and NH₃)_{3}) of atmospheric interest on electron impact at energies from threshold to 2000 eV. We have employed the complex scattering potential – ionization contribution (CSP-ic) method for the present study. Attempt has been made to improve the method by computing the parameter that involves the ratio of sum of the total excitation cross sections (Σ Q _exc ) and total inelastic cross section (Q _inel ) at the peak of the inelastic cross section. The present study not only provided a better estimation of the parameter involved in the CSP-ic method but also provided better agreement with the available experimental and theoretical data on the ionization cross sections of the simple atomic and molecular targets studied here.     

Ne原子与HF分子碰撞振转激发分波截面的研究

采用单双取代并加入三重激发项校正的二次组态相互作用QCISD(T)方法, 以及aug-cc-pVTZ基组对Ne-HF分子间相互作用势进行了计算, 并考虑了Boys和Bernardi提出的均衡法, 在计算的基础上消除基组重叠误差. 计算得到了11个方向的Ne-HF碰撞系统的相互作用势能点数据, 使用Huxley势函数对数据点进行非线性最小二乘法拟合, 计算了各向异性势的径向系数V₀, V₁, V₂, V₃等, 其函数形式能够很好地描述Ne原子与HF分子碰撞系统的势能面; 采用密耦近似计算得到了Ne原子与HF分子碰撞系统不同能量下的总截面、 弹性分波截面和非弹性分波截面. 关键词： He-HF 碰撞 相互作用势 密耦近似     

Rotational relaxation in ultracold He+BH collisions

Collisions of cold and ultracold BH in the v=0 level with the He atom are investigated using the quantum mechanical scattering formulation. The elastic and the inelastic cross sections are calculated using the two-dimensional ab initio potential energy surface. It is shown that the elastic cross section is larger than the inelastic one. When the collision energy is very low, the elastic cross section follows the Wigner threshold law and is one order of magnitude larger than that of He-O₂, while it is much smaller than that of He-H₂. The efficiency of the rotationally quenching state is given. The Δj=-1 transition is most efficient. The resonances are also found to occur at about the same translational energy (0.1-1 cm^-1), which gives rise to steps in the rate coefficient at temperatures around 0.1-1 K.     

Electron impact total cross section calculations for CH3SH (methanethiol) from threshold to 5 keV

We report calculated total elastic cross sections Q_el, total ionisation cross sections, Q_ion, summed total excitation cross sections ∑Q_exc and total cross sections Q_T for CH₃SH upon electron impact for energies from ionisation threshold to 5 keV. We have employed Spherical Complex Optical Potential (SCOP) formalism to calculate total elastic cross section Q_el, and total inelastic cross section Q_inel and used Complex Scattering Potential – the ionisation contribution (CSP-ic) method to extract the ionisation cross sections, Q_ion, from the calculated Q_inel. The calculated total cross sections are examined as functions of incident electron energy and are compared with available data wherever possible and overall good agreement is observed. In this work Q_el, Q_ion, and ∑Q_exc are reported for the first time for CH₃SH in this energy range.     

Total reaction and fusion cross sections at sub- and near-barrier energies for the system 7Li + 28Si

Fusion cross sections are extracted for the ⁷Li$ + $²⁸Si system, via reaction cross section and transfer measurements at sub- and near-barrier energies ( E _lab = 5.7 to 14MeV). The energy evolution of transfer to reaction cross section ratios is determined with the aid of CDCC calculations, which subsequently allows the deduction of fusion cross sections at sub- and near-barrier energies. It is shown that fusion can be well represented in a BPM context. Fusion cross sections are compared for the systems ⁷Li$ + $²⁸Si and ⁶Li$ + $²⁸Si, the latter studied previously, and are found to exhibit different strengths. Last, the direct channels determined at 13MeV, are found to be dominated by a 2n -transfer mechanism.     

He-Na2体系低温下的冷碰撞研究

在已经拟合好的He-Na₂体系势能面上,根据原子-双原子分子的非反应性碰撞动力学的相关基本理论,在空间固定坐标系下,采用严格的密耦方法求解了He原子和Na₂分子的转动非弹性碰撞动力学方程.并对He-Na₂体系的微分散射截面、积分截面作了详细的分析,结果与实验符合得比较好.结果表明：（1）弹性散射（Δj=0）截面远大于非弹性截面;（2）较小Δj的跃迁主要产生前向散射,随着Δj的增加,后向散射的几率增加 关键词： 2体系')" href="#">He-Na₂体系 密耦方法 微分散射截面 积分截面     

Top-quark mediated effects in hadronic Higgs-Strahlung

Novel contributions to the total inclusive cross section for Higgs-Strahlung in the Standard Model at hadron colliders are evaluated. Although formally of order a_s²\alpha_{s}^{2}, they have not been taken into account in previous NNLO predictions. The terms under consideration are induced by Higgs radiation off top-quark loops and thus proportional to the top-quark Yukawa coupling. At the Tevatron, their effects to WH production are below 1% in the relevant Higgs mass range, while for ZH production, we find corrections between about 1% and 2%. At the LHC, the contribution of the newly evaluated terms to the cross section is typically of the order of 1%–3%. Based on these results, we provide updated predictions for the total inclusive Higgs-Strahlung cross section at the Tevatron and the LHC.     

Spin structure of the “Forward” nucleon charge-exchange reaction <Emphasis Type="Italic">n</Emphasis> + <Emphasis Type="Italic">p</Emphasis> → <Emphasis Type="Italic">p</Emphasis> + <Emphasis Type="Italic">n</Emphasis> and the deuteron charge-exchange breakup

The structure of the nucleon charge-exchange process n + p → p + n is investigated basing on the isotopic invariance of the nucleon-nucleon scattering. Using the operator of permutation of the spin projections of the neutron and proton, the connection between the spin matrices, describing the amplitude of the nucleon charge-exchange process at zero angle and the amplitude of the elastic scattering of the neutron on the proton in the “backward” direction, has been considered. Due to the optical theorem, the spin-independent part of the differential cross section of the process n + p → p + n at zero angle for unpolarized particles is expressed through the difference of total cross sections of unpolarized proton-proton and neutron-proton scattering. Meantime, the spin-dependent part of this cross section is proportional to the differential cross section of the deuteron charge-exchange breakup d + p → (pp) + n at zero angle at the deuteron momentum k _d = 2 k _n (k _n is the initial neutron momentum). Analysis shows that, assuming the real part of the spin-independent term of the “forward” amplitude of the process n + p → p + n to be smaller or of the same order as compared with the imaginary part, in the wide range of neutron laboratory momenta k _n > 700 MeV/c the main contribution into the differential cross section of the process n + p → p + n at zero angle is provided namely by the spin-dependent term.     

On the strong influence of inner shell resonances upon the outer shell photoionization of endohedral atoms

It is demonstrated by the example of the Xe atom stuffed inside the C₆₀ fullerene, i.e., the endohedral Xe@C₆₀, that the so-called confinement resonances in 4d subshell strongly affect the photoionization cross section of outer 5p and subvalent 5s electrons near the 4d ionization threshold. It is a surprise that these narrow inner 4d shell resonances are not smeared out in the outer shell photoionization cross section. On the contrary; the inner shell resonances affect the outer cross section by enhancing them enormously. Close to its own photoionization thresholds, 5p and 5s photoionization cross sections of Xe@C₆₀ are dominated by their own confinement resonances greatly affected by the amplification of the incoming radiation intensity due to polarization by it of the C₆₀ electron shell. Between 4d and 5p thresholds, the effect of 4d is becoming stronger while own resonances of 5p and 5s are becoming much less important.     

Ionization of hydrogen and helium atoms by highly charged fast ions in collisions with small momentum transfer

Ionization of hydrogen and helium atoms is studied for the case of “soft” collisions with highly charged fast ions with v≲Z≪v² and v≫v ₀, where Z is the ion charge, v is the collision velocity, and v ₀∼1 is the characteristic velocity of the electron in the ground state of the atom. Analytical expressions are derived for the singly and doubly differential cross section for ionization of a hydrogen atom accompanied by the ejection of a slow electron v _e≲v ₀, where v _e is the velocity of the ejected electron with respect to the recoil ion). The results are generalized to the case of single ionization of helium. It is shown that soft collisions provide the main contribution to the hydrogen ionization cross section and for all practical purposes determine the cross section for single ionization of helium. The asymmetry in the angular distribution of the ejected slow electrons and the properties of momentum exchange in such collisions are discussed. Finally, a formula for the cross section for single ionization of helium is proposed. Zh. éksp. Teor. Fiz. 112, 1966–1977 (December 1997)     

Cq+(q=1-4)与He,Ne,Ar碰撞的电子损失截面测量与研究

在中能区测量了C^q+(q=1-4)与He,Ne,Ar气体原子碰撞的电子损失截面,计算分析了入射离子损失两个电子与一个电子的总截面比 R₂₁. 单反应道分析无法完全解释所有实验结果,必须同时考虑入射离子的电子损失、电子俘获和靶原子电离各种出射道间的耦合作用. 对于不同靶原子的碰撞,入射离子损失一个电子和两个电子的速度阈值可以由屏蔽和反屏蔽理论解释. 然而,该理论不能完全解释截面比 R₂₁ 关键词： 离子-原子碰撞 截面 电子损失     

Associated production of a KK-graviton with a Higgs boson via gluon fusion at the LHC

In order to solve the hierarchy problem, several extra-dimensional models have received considerable attention. We have considered a process where a Higgs boson is produced in association with a KK-graviton (G _KK) at the LHC. At the leading order, this process occurs through the gluon fusion mechanism gg→hG _KK via a quark loop. We compute the cross section and examine some features of this process in the ADD model. We find that the quark in the loop does not decouple in the large quark-mass limit just as in the case of gg→h process. We compute the cross section of this process for the case of the RS model also. We examine the feasibility of this process being observed at the LHC.     

Cross section for the production of compound nuclei in <Emphasis Type="Italic">p</Emphasis>Bi interaction at energies in the range 20–100 MeV

A method for determining the cross section for compound-nucleus formation, σ _CN, in nuclear reactions initiated by protons of energy in the range 20–100 MeV is proposed. The method is based on measuring cross sections for the yield of isotopes maximally remote from the target nucleus. The applicability of the method is illustrated by applying it to the reaction ²⁰⁹Bi(p, xn), which is considered by way of example. Data obtained for the cross section σ _CN are compared with the results of calculations performed on the basis of the intranuclear-cascade model.     

Stopping cross sections of 50- to 230-keV nitrogen ions in silicon measured by ion backscattering spectroscopy

The energy dependence of the total stopping cross section of 50- to 230-keV nitrogen ions in silicon (σ _S (E)) is measured in order to develop the diagnostics of heavy impurities in films of a nanometer thickness by heavy ion backscattering (HIBS) spectroscopy. At ion energies lower than 150 keV, this σ _S (E) dependence occupies an intermediate position between the dependences given in the SRIM and MSTAR data-bases; at higher energies, our dependence is closer to the former dependence. The estimation of the effect of inelastic processes on the stopping cross section demonstrates that the effect of these processes for nitrogen ions can be neglected when heavy impurities in such films are studied by HIBS.