First measurement of the ratio of central-electron to forward-electron W partial cross sections in pp[over] collisions at (square root)s =1.96 TeV

We present a measurement of sigma(pp[over] --> W) x B(W --> e nu) at (square root)s = 1.96 TeV, using electrons identified in the forward region (1.2 < |eta| < 2.8) of the CDF II detector, in 223 pb(-1) of data. We measure sigma x B = 2796 +/- 13(stat)(-90)(+95)(syst) +/- 162(lum) pb. Combining this result with a previous CDF measurement obtained using electrons in the central region (|eta| approximately < 1), we present the first measurement of the ratio of central-electron to forward-electron W partial cross sections R(exp) = 0.925 +/- 0.006(stat) +/- 0.032(syst), consistent with theoretical predictions using Coordinated Theoretical-Experimental Project on QCD (CTEQ) and Martin-Roberts-Stirling-Thorne (MRST) parton distribution functions.     

次近邻相互作用对Heisenberg XX链纠缠影响的研究

研究了存在次近邻相互作用(耦合)时Heisenberg XX链的纠缠特性. 结果表明对近邻格点, 随着耦合常数J的变化, 次近邻相互作用的存在可能使其纠缠度增大或者减小; 而对次近邻格点, 引进次近邻相互作用却可以产生纠缠, 并且使其随着|J|的增大而增大. 近邻格点间纠缠存在的临界温度T_c随着J的增大而降低, 次近邻格点间纠缠存在的临界温度T_c随着|J|的增大而升高. 此外对纠缠W态的制备, 次近邻相互作用的存在还使得三量子位情形时W态产生的时刻改变, 而对于四量子位情形却没有影响.     

成键元素的电子声子相互作用的特征

本文在Bardeen和Pines确定的电子-声子相互作用的有效矩阵元的基础上,讨论了元素之间有化学键的形成,元素之间发生了电子转移,元素的核外层电子发生了变化对电子-声子相互作用的影响.所得结果和Bardeen和Pines,Bohm和Pines早期的工作符合,可由下列事实解释：即元素成键后,成键电子转移后元素的剩余的电...     

First measurements of inclusive W and Z cross sections from run II of the fermilab tevatron collider

We report the first measurements of inclusive W and Z cross sections times leptonic branching ratios for pp collisions at square root[s]=1.96 TeV, based on their decays to electrons and muons. The data correspond to an integrated luminosity of 72 pb(-1) recorded with the CDF detector at the Fermilab Tevatron. We test e-mu universality in W decays, and we measure the ratio of leptonic W and Z rates from which the leptonic branching fraction B(W-->lnu) can be extracted as well as an indirect value for the total width of the W and the Cabibbo-Kobayashi-Maskawa matrix element, |V(cs)|.     

激光功率密度对Al膜靶后表面快电子发射的影响

 报道了在20 TW皮秒激光器上完成的p偏振激光与等离子体相互作用过程中产生的快电子的角分布和能谱测量结果。实验得到：当激光功率密度小于10¹⁷ W/cm²时,电子发射没有明显定向性,在激光入射面内多峰发射;当激光功率密度大于10¹⁷ W/cm2,小于10¹⁸ W/cm²时,电子主要沿靶面法线方向发射;当激光功率密度达到相对论强度时,电子主要沿激光传播方向发射;激光功率密度未达到相对论强度时,靶后表面法线方向快电子能谱拟合平均温度符合共振吸收温度定标率;激光功率密度达相对论强度以上时,靶后表面法线方向快电子能谱拟合平均温度高于已有的温度定标率。     

具有对称和反对称超交换相互作用的一维spin-Peierls系统的基态行为

采用Lanczos数值计算方法研究了具有Dzyaloshinskii-Moriya（DM）相互作用和Kaplan-She khtman-Entin-Wohlman-Aharony（KSEA）相互作用的一维spin-Peierls（s-P）系统的基态 行为.计算结果发现KSEA相互作用总是不利于系统二聚化，并且它还影响DM相互作用对系统 二聚化的贡献，甚至可以抵消其作用；在某些特定条件下, KSEA和DM的共同作用可以破坏系 统的二聚化基态而转化为均匀基态. 关键词： DM相互作用 KSEA相互作用 二聚化     

Is there really evidence for attractive interactions in single band fermion systems with strong on site repulsion?

It is often claimed that strong on site electronic interactions and correlations lead to neighbor attractions, offering a new mechanism for superconductivity. Here it will be demonstrated that for the single band case, there is a neighbor repulsion between electrons. It is hidden by a finite size effect which has dominated all results obtained so far.     

Electron clusters in inert gases

This Letter addresses the counterintuitive behavior of electrons injected into dense cryogenic media with negative scattering length L. Instead of strongly reduced mobility at all but the lowest densities due to the polaronic effect involving the formation of density enhancement clusters (expected in the theory with a simple gas-electron interaction successfully applied earlier to electrons in helium where L>0) which should substantially decrease the electron mobility, an opposite picture is observed: with increasing |L| (the trend taking place for inert gases with the growth of atomic number) and the gas density, the electrons remain practically free. An explanation of this behavior is provided based on consistent accounting for the nonlinearity of the electron interaction with the gaseous medium in the gas atom number density.     

Effect of flux-dependent Friedel oscillations upon the effective transmission of an interacting nano-system

We consider a nano-system connected to measurement probes via non interacting leads. When the electrons interact inside the nano-system, the coefficient |t_s(E_F)|² describing its effective transmission at the Fermi energy E_F ceases to be local. This effect of electron-electron interactions upon |t_s(E_F)|² is studied using a one dimensional model of spinless fermions and the Hartree-Fock approximation. The non locality of |t_s(E_F)|² is due to the coupling between the Hartree and Fock corrections inside the nano-system and the scatterers outside the nano-system via long range Friedel oscillations. Using this phenomenon, one can vary |t_s(E_F)|² by an Aharonov-Bohm flux threading a ring which is attached to one lead at a distance L_c from the nano-system. For small distances L_c, the variation of the quantum conductance induced by this non local effect can exceed 0.1 (e²/h).     

H原子(e,2e)反应中电子角分布的理论研究

使用3C和DS3C模型,计算了不同入射能情形下电子入射离化H原子的三重微分截面,并对截面的结构进行了分析.结果表明:角分布基本上由两个峰组成,即binary峰和recoil峰.两个峰的形状和位置对两个出射电子的能量分配及探测的几何条件十分敏感.更进一步,末态电子与电子的排斥对形成观测到的角分布有显著的贡献,在不同几何条件下,三体相互作用通过不同散射幅的不同权重控制了干涉花样.此外,对直接和交换效应也都进行了研究. 关键词： 角分布 binary峰 recoil峰     

Tensor rank and stochastic entanglement catalysis for multipartite pure states

The tensor rank (also known as generalized Schmidt rank) of multipartite pure states plays an important role in the study of entanglement classifications and transformations. We employ powerful tools from the theory of homogeneous polynomials to investigate the tensor rank of symmetric states such as the tripartite state |W3>=1/√3(|100> + |010> + |001>) and its N-partite generalization |W(N)>. Previous tensor rank estimates are dramatically improved and we show that (i) three copies of |W3> have a rank of either 15 or 16, (ii) two copies of |W(N)> have a rank of 3N - 2, and (iii) n copies of |W(N)> have a rank of O(N). A remarkable consequence of these results is that certain multipartite transformations, impossible even probabilistically, can become possible when performed in multiple-copy bunches or when assisted by some catalyzing state. This effect is impossible for bipartite pure states.     

The influence of dielectric properties on the emission of a metal-dielectric-metal system: Elastic scattering,optical phonons

The influence of electron-phonon interactions in a dielectric on the emission current and the transfer ratioα is investigated. A simple model of a thin-film field cathode, based on the tunnel effect between the first metal and the dielectric, has been proposed for this purpose. In the dielectric the tunnelling electrons can lose energy by collisions with phonons and flaws, and in the top electrode by collisions with electrons of metal 2. After some simplifications the transfer ratio α is obtained. The expressions forα are then discussed and compared with other models. It is shown that if the appropriate parameters are chosen for the cathode, the effect of the phonons will be negligible.     

The Equilibrium Distribution for Free Electrons in a Real Gas

The equilibrium distribution for free electrons in a real gas is derived based on the existence of an interaction potential between a free electron and its nearest neighbor atom (or ion). The form of the interaction potential is inversely proportional to rl where l is a constant; and the derived distribution reduces to the Maxwellian form when the interaction is neglected. It is shown that for most physical situations this interaction potential will only contribute a miniscule change to those electron properties which are dependent upon<|vj?>, j>-3 where is the electron speed.     

Spin-Wave Excitations and Energy Gap in Quasi-One-Dimensional Organic Polymer Ferromagnets

Based on a theory model proposed for organic ferrornagnets, the spin configuration and spinwave excitations in quasi-one-dimensional organic polymer ferromagnets are studied. The results show that: 1) Owing to the unpaired electrons at side free-radicals, the degeneracy of the spin-wave will be removed, the lower branch of the spin-wave excitations will split off into two branches, and it shows ferromagnetic characters; 2) The anisotropic interactions between the unpaired electrons at side free-radicals will make an energy gap appear between the ground state and the lowest excited state.     

Unusual symmetries in the Kugel-Khomskii Hamiltonian

The Kugel-Khomskii Hamiltonian for cubic titanates describes spin and orbital superexchange interactions between d(1) ions having threefold degenerate t(2g) orbitals. Since orbitals do not couple along "inactive" axes, perpendicular to the orbital planes, the total number of electrons in |alpha> orbitals in any such plane and the corresponding total spin are both conserved. A Mermin-Wagner construction shows that there is no long-range spin ordering at nonzero temperatures. Inclusion of spin-orbit coupling allows such ordering, but even then the excitation spectrum is gapless due to a continuous symmetry. Thus, the observed order and gap require more symmetry breaking terms.     

Near QED regime of laser interaction with overdense plasmas

Interaction of laser plulses with intensities up to 10²⁵?W/cm² with overdense plasma targets is investigated via three-dimensional particle-in-cell simulations. At these intensities, radiation of electrons in the laser field becomes important. Electrons transfer a significant fraction of their energy to γ-photons and obtain strong feedbacks due to radiation reaction (RR) force. The RR effect on the distribution of laser energies among three main species: electrons, ions and photons is studied. The RR and electron-positron pair creation are implemented by a QED model. As the laser intensity inreases, the ratio of laser energy coupled to electrons drops while the one for γ-photons reaches up to 35%. Two distinctive plasma density regimes of the high-density carbon target and low-density solid hydrogen target are identified from the laser energy partitions and angular distributions of photons. The power-laws of absorption efficiency versus laser intensity and the transition of photon divergence are revealed. These show enhanced generation of γ-photon beams with improved collimation in the relativistically transparent regime. A new effect of transverse trapping of electrons inside the laser field caused by the RR force is observed: electrons can be unexpectedly confined by the intense laser field when the RR force is comparable to the Lorentz force. Finally, the RR effect and different regions of photon emission in laser-foil interactions are clarified.     

合金化成分对NiTi合金M_s点影响的正电子湮没研究

用双探头符合系统测量了金属Fe、Co、Ni、Al、Nb、Cu、Ti和NiTi合金的多普勒展宽谱,计算了其S参数和W参数,分析了合金中d-d金属键的作用.结果表明,当用Fe、Co或Al原子加入NiTi合金时,都将使合金中参与形成d-d金属键的d电子减少,从而使金属键减弱;而用Cu或Nb原子加入NiTi合金时,对合金中d-d电子作用的影响很小,合金中共价键的成分变化不大.在NiTi合金中加入合金化元素可以改变其电子结构,进而影响Ms点.     

Dose estimation and shielding calculation for X-ray hazard at high intensity laser facilities

An ionizing radiation hazard produced from the interaction between high intensity lasers and solid targets has been observed. Laser-plasma interactions create "hot" electrons, which generate bremsstrahlung X-rays when they interact with ions in the target. However, up to now only limited studies have been conducted on this laser-induced radiological protection issue. In this paper, the physical process and characteristics of the interaction between high intensity lasers and solid targets are analyzed. The parameters of the radiation sources are discussed, including the energy conversion efficiency from laser to hot electrons, hot electron energy spectrum and electron temperature, and the bremsstrahlung X-ray energy spectrum produced by hot electrons. Based on this information, the X-ray dose generated with high-Z targets for laser intensities between 10¹⁴ and 10²⁰ W/cm² is estimated. The shielding effects of common shielding items such as the glass view port, aluminum chamber wall and concrete wall are also studied using the FLUKA Monte Carlo code. This study provides a reference for the dose estimation and the shielding design of high intensity laser facilities.     

电子经过介质由于介质被极化影响能量损失的研究

电子经过介质时,将介质极化,本工作的目的是研究较低能量的电子经过不同介质时,由于这种极化效应对于电子能量损耗的影响。利用灌氢气的膨胀式云雾室测量了能量为0.3—1.0Mev的电子经过铍、炭及铝片的平均能耗及最大可几能耗。实验指出:在此能量范围内的电子,经过某些介质,它们的传导电子数与全部电子数的比值f₀以及电阻系数ρ都大,如铍及炭,其能量损耗由于介质被极化而显著减少。电子经过铍的能耗实验结果显著比考虑了介质极化影响的Helpern及Hall与电子能量损耗有显著减少Sterneimer的理论为小;电子经过炭的能耗实验结果是介于此二理论之间。     

Origin of the blueshift in the infrared absorbance of intersubband transitions in N/GaN multiple quantum wells

A self-consistent calculation of the subband energy levels of n-doped quantum wells is studied. A comparison is made between theoretical results and experimental data. In order to account for the deviations between them, the ground-state electron–electron exchange interactions, the ground-state direct Coulomb interactions, the depolarization effect, and the exciton-like effect are considered in the simulations. The agreement between theory and experiment is greatly improved when all these aspects are taken into account. The ground-to-excited-state energy difference increases by 8 meV from its self-consistent value if one considers the depolarization effect and the exciton-like effect only. It appears that the electron–electron exchange interactions account for most of the observed residual blueshift for the infrared intersubband absorbance in Al_xGa_1-xN/GaN multiple quantum wells. It seems that electrons on the surface of the k-space Fermi gas make the main contribution to the electron–electron exchange interactions, while for electrons further inside the Fermi gas it is difficult to exchange their positions.