低能电子碰撞He+(e,2e)反应绝对三重微分截面的理论研究

利用Berakdar和Briggs对BBK波函数Sommerfeld参数的修正结果，即考虑第三个粒子存在对两个粒子间相互作用的影响，考虑了入射道的库仑相互作用及出射粒子的交换对称性，计算了在共面等能分配几何情况下低能电子碰撞He⁺(e,2e)反应绝对三重微分截面.结果表明，入射道库仑场对较低的入射能量及小的碰撞参数的三重微分截面影响较大. 关键词：     

Li+低能(e,2e)反应角分布

利用修正的BBK理论，考虑入射道的库仑相互作用及出射电子的交换对称性，在共面-等能分享-垂直角度碰撞几何中，分别计算了能量为79.6，105.6，227.6和375.6eV的入射电子碰撞Li⁺(1s²)(e，2ｅ)反应三重微分截面(TDCS).结果表明：在接近阈能的碰撞中，两出射电子连线平行于入射电子方向时，TDCS最大；两出射电子连线垂直于入射电子方向时，TDCS最小；入射电子能量达5倍的电离阈能时，主要为单次双体碰撞，而且入射道库仑场对决定低能碰撞的TDCS起着重要作用. 关键词：     

离子极化势对钙原子共面对称(e,2e)反应影响的数值研究

本文使用扭曲波波恩近似方法(DWBA)研究了共面对称条件下钙原子的电子碰撞电离反应((e,2e)反应),在DWBA理论的基础上,考虑了原子极化势和离子极化势对三重微分散射截面的影响.采用发展的DWBA方法,我们研究了出射电子能量从6.75 e V到29.25 e V范围内电子与钙原子的碰撞电离过程,计算了电离三重微分截面.通过与已有理论和实验数据进行比较发现,离子极化势对钙原子的共面对称(e,2e)反应散射微分截面有较大的影响,很好的描述了碰撞电离微分截面的结构效应,特别是在散射角度较小时(≦60o),本文计算结果与实验测量非常一致.     

电子碰撞类氢离子电离非相对论跃迁矩阵元

利用BBK模型,导出了电子-类氢离子碰撞电离跃迁矩阵元的解析形式。出射道用包含三个适当的合流超几何函数,且满足适当的三体库仑边界条件的关联BBK波函数来描述,入射道考虑了入射电子与靶离子的长程库仑相互作用而包括一库仑波。含有四个合流超几何函数在内的跃迁T-矩阵元的六维空间积分已约化为一包含高斯-超几何函数的三维实参数积分。忽略入射电子与靶离子的库仑相互作用时,表示用平面波描述的入射电子与靶离子的碰撞,再取靶离子电荷数Z=1时,表示氢原子的电离;略去排斥因子(α₁₂=0)时,又表示不考虑关联的电离。从而可分析各种情况的电离性质。在目前离子的(e,2e)反应三微分截面实验数据还不具备的情况下,可先提供一些必要的理论结果。进而可广泛地应用于处理散射问题之中。     

共面双对称几何中Li+(1s2)(e,2e)反应的理论研究

利用Berakdar理论,考虑了入射道的库仑相互作用,在共面双对称碰撞几何中,计算了能量为251eV入射电子碰撞Li⁺(1s²)(e,2e)反应的三重微分截面(TDCS),讨论了不同散射振幅对截面的贡献,分析了干涉效应及入射道库仑场对截面的影响.结果表明,它们对决定TDCS的角度分布和大小起着重要作用. 关键词：     

共面不对称条件下He和Ar原子（e, 2e）反应过程中的极化效应和后碰撞相互作用

采用修正后的扭曲波玻恩近似(DWBA)理论,计算了共面不对称几何条件及大能量转移和小动量转移条件下的He(1s²),Ar(3p⁶)和Ar(2p⁶)(e, 2e)反应三重微分截面.将理论计算结果与实验结果及由Brauner,Briggs和Klar提出的BBK方法、标准的DWBA理论计算结果进行了比较,发现在共面不对称几何条件及大能量转移和小动量转移条件下,极化效应和后碰撞相互作用在He(1s²),Ar(3p^{6< 关键词： (e;2e)反应 极化效应 后碰撞相互作用 共面不对称几何条件}     

离子极化势对钙原子共面对称(e,2e)反应影响的数值研究

本文使用扭曲波波恩近似方法(DWBA)研究了共面对称条件下钙原子的电子碰撞电离反应( (e,2e)反应 ),在DWBA理论的基础上,考虑了原子极化势和离子极化势对三重微分散射截面的影响。采用发展的DWBA方法,我们研究了出射电子能量从6.75eV到29.25eV范围内电子与钙原子的碰撞电离过程,计算了电离三重微分截面。通过与已有理论和实验数据进行比较发现,离子极化势对钙原子的共面对称(e,2e)反应散射微分截面有较大的影响,很好的描述了碰撞电离微分截面的结构效应,特别是在散射角度较小时(≦60o),本文计算结果与实验测量非常一致。     

共面不对称条件下Ag+(4p,4d)(e,2e)反应三重微分截面的理论研究

采用扭曲波玻恩近似(DWBA)理论计算了共面不对称几何条件下Ag⁺(4p⁶) 及Ag⁺(4d¹⁰)在不同入射电子能量和散射电子角度下(e,2e)反应的三重微分截面. 散射电子角度为4°, 10°和20°. 计算结果表明, Ag⁺(4p⁶)(e,2e)反应的三重微分截面其binary峰峰位或劈裂峰的谷位与动量转移方向有较大差别, 这可能是由于一种两次两体碰撞造成的. 另外, 还发现Ag⁺(4p⁶)(e,2e)反应三重微分截面的binary峰出现了反常劈裂现象, 这表明离子靶内壳层电离(e,2e)反应过程较外壳层更为复杂.对Ag⁺(4p⁶)及Ag⁺(4d¹⁰), 除binary峰和recoil峰以外, 在其他敲出电子角度出现了新的峰, 本文用几种两次两体碰撞过程对这些新的峰进行了解释.     

电子碰撞原子(e,2e)反应的复极化势

研究包括连续通道等非处理通道的复极化势对(e,2e)碰撞过程三重微分截面的影响,即将耦合通道光学势方法得到的复极化势附加到畸变波玻恩近似方法的畸变势中,在靶态的HF近似下,计算了Ar原子和Ne原子在非共面对称几何条件下(e,2e)反应的三重微分截面.对于较高的入射能量,在实验的误差范围内,计算结果与电子动量谱的实验数据符合较好,复极化势的影响很小;对于较低的入射能量,复极化势的作用明显增大. 关键词： 复极化势 (e;2e)反应 三重微分截面 电子动量谱     

He原子(e,3e)反应中末态波函数的动量相关

在前期工作的基础上,进一步考虑了He原子(e,3e)反应中末态四体的动量相关.用改进后的理论计算了高能电子入射双电离He原子的五重微分截面(FDCS).与前期理论相比,所得结果大大地改善了理论曲线与实验结果的吻合程度.     

Measurements of the absolute branching fractions for D→K̄πe+νe, D→K̄*e+νe and determination of Γ(D+→K̄*0e+νe)/Γ(D+→K̄0e+νe)

Using the data of about 33 pb^-1 collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we have studied the exclusive semileptonic decays D⁺→K^-π⁺e⁺ν_e, D⁰→K̄⁰π^-e⁺ν_e, D⁺→K̄^*0e⁺ν_e and D⁰→K^*-e⁺ν_e. The absolute branching fractions for the decays are measured to be BF(D⁺→K^-π⁺e⁺ν_e)=(3.50±0.75±0.27)%, BF(D⁰→K̄⁰π^-e⁺ν_e)=(2.61±1.04±0.28)%, BF(D⁺→K̄^*0e⁺ν_e)=(5.06±1.21±0.40)% and BF(D⁰→K^*-e⁺ν_e)=(2.87±1.48±0.39)%. The ratio of the vector to pseudoscalar semileptonic decay rates Γ(D⁺→K̄^*0e⁺ν_e)/Γ(D⁺→K̄⁰e⁺ν_e) is determined to be 0.57±0.17±0.02.     

Radiative corrections to the reactione + e -→e + e -π+π-

The radiative corrections to the reactione ⁺ e ^-→e ⁺ e ^-π⁺π^- are calculated to order α⁵ for an experiment without electron tagging and where the acceptance of the central detector is limited by angular and momentum cuts. The total radiative correction is found to be smaller than a few percent from 1.5 to 70 GeV.     

Graviton-induced bremsstrahlung at e + e - colliders

We consider graviton-induced bremsstrahlung at future e ⁺ e ^- colliders in both the ADD and RS models, with emphasis on the photon perpendicular momentum and angular distribution. The photon spectrum is shown to be harder than in the standard model, and there is an enhancement for photons making large angles with respect to the beam. In the ADD scenario, the excess at large photon perpendicular momenta should be measurable for values of the cut-off up to about twice times the CM energy. In the RS scenario, radiative return to graviton resonances below the CM energy can lead to large enhancements of the cross section.Received: 28 March 2004, Published online: 3 June 2004     

Properties of anomalous eμ events produced in e+e− annihilation

We present the properties of 105 events of the form e⁺ + e^? → e^+- + μ^? + missing energy, in which no other charged particles or photons are detected. The simplesthypothesis compatible with all the data is that these events come from the production of a pair of heavy leptons, the mass of the lepton being in the range 1.6 to 2.0 GeV/c²     

A measurement of the reaction e+e- →e+e-η′ and the radiative width Γη′→γγ at petra

The reaction e⁺e^- → e⁺e^-η' has been observed in the JADE experiment at PETRA, by detecting the final state π⁺π^-γ, resulting from the decay η' → γ?⁰. The cross section was measured at an average beam energy of 17.15 GeV to be σ(e⁺e^- → e⁺e^-η') = 2.2 ± 0.2 (stat.) ± 0.4(syst.) nb, yielding the radiative width Γ_η'γγ= 5.0 ± 0.5(stat.) ± 0.9 (syst.) keV.     

Hunting new vector bosons in high precision measurements without polarization

We illustrate a strategy to identify the effect of a possible extra neutral vector boson of several different theoretical origins (extended gauge groups, composite models, models with a strongly interacting Higgs sector), assuming that only precision experiments without polarized e⁺e⁻ beams were available. We show that it might be relatively easy to discover evidence of genuine New Physics (i.e., effects not depending on the value of the top mass, or on the existence of new families...) if a certain set of observables, including the final τ polarization in unpolarized e⁺e⁻ annihilation, were measured. The region of possible confusion between different theoretical models would be, though, sensibly larger than in the case in which e⁺e⁻ polarization were available.     

Searching for the process e+e- → K+K-π0 in experiments with the spherical neutral detector at VEPP-2M

We have searched for the process e⁺e^- → K⁺K^-π⁰ at energies up to 1.38 GeVin an experiment with the spherical neutral detector at the VEPP-2M e⁺e^- collider. The upper limits of the cross sections for the processes σ(e⁺e →; φπ: → K⁺K^-π⁰) < 0.023 nb and σ(e⁺e^- → KK*(892) → K⁺K^-π⁰) < 0.059 nb have been established at a 95% confidence level.     

Formation of negative hydrogen ion in positronium-hydrogen collisions

The importance of the excited states of Positronium (Ps) in the formation cross sections (both differential and total) of the negative hydrogen ion (H^-) are investigated theoretically for the charge transfer reaction, Ps (n = 1, 2) + H ↦ e⁺ + H^- for a wide range of incident energies (e.g., threshold – 500 eV). The calculations are performed in the frame work of a qualitative model, the post collisional Coulomb modified eikonal approximation (CMEA). A comparative study is also made between the capture from ground and excited states of the Ps. The present CMEA model takes account of higher order effects which is essential for a rearrangement process where the first Born type approximation (Coulomb Born for the ionic case) is not supposed to be adequate. At low incident energies, the excited states of Ps (2s, 2p) are found to play a dominant role in the H^- formation cross sections. Significant deviations are noted between the present CMEA and the Coulomb Born (CBA) results even at very high incident energies (e.g., E_i = 500 eV), indicating the importance of higher order effects. At high incident energies the present CMEA differential cross section (DCS) exhibits a double peak structure which is totally absent in the CBA and could again be attributed to higher order effects.     

Charged majorons ine + e − ande − e − collisions

The experimental limits on charged majorons, i.e. charged scalars which carry lepton number, are discussed in a model independent way. Possible signals ine ⁺ e ^? ande ^? e ^? collisions are then estimated. It is stressed that the limits on majorons which conserve the different lepton flavors separately are presently very poor. These limits can however be improved by studyinge ^? e ^? collisions.     

Effective-Lagrangian approach to γγ→WW II: Results and comparison with e+e-→WW

We present a study of anomalous electroweak gauge-boson couplings that can be measured in e⁺e^- and γγ collisions at a future linear collider like ILC. We consider the gauge-boson sector of a locally SU(2)×U(1) invariant effective Lagrangian with ten dimension-six operators added to the Lagrangian of the standard model. These operators induce anomalous three-gauge-boson and four-gauge-boson couplings and an anomalous γγH coupling. We calculate the reachable sensitivity for the measurement of the anomalous couplings in γγ→WW. We compare these results with the reachable precision in the reaction e⁺e^-→WW on the one hand and with the bounds that one can obtain from high-precision observables in Z decays on the other hand. We show that one needs both the e⁺e^- and the γγ modes at an ILC to constrain the largest possible number of anomalous couplings and that the Giga-Z mode offers the best sensitivity for certain anomalous couplings.