e+e－反应中共振截面的辐射修正

本文导出了e⁺e^－对撞实验中产生的共振态的辐射修正截面的近似解析公式.对于Z⁰粒子和J/ψ,Υ家族的粒子,在确定这些共振态参数的实验扫描能量范围内,该解析近似的精度达到0.1%量级.利用解析近似公式与对撞束能量分辨函数的卷积拟合实验观测到的共振截面数据,可得到比当前普遍采用的Jackson,Scharre方法更准确的共振参数值.     

K—K共振态

最近实验指出,在π^-+p→K+K+n以及K^-+p→K+K+A反应中,存在K-K的共振态,共振能量为1.02BeV。不少人对K-K共振态进行了分析,但并没得出一致的结论。本文从场论观点出发,在链式近似下,研究了有关K-K共振的一些问题,计算结果表明,在1.02BeV附近可能存在两个共振态,而1.02BeV的K-K共振对应T=0,J^PG++态较为合理。     

J/ψ辐射衰变中θ(1720)宽共振峰的矩分析

本文用矩分析法对J/ψ辐射衰变产生的θ(1720)宽共振峰的结构进行了研究.由于f'₂(1525)和θ(1720)二共振峰有重迭,为此我们讨论了2⁺⁺(f'₂(1525))+0⁺⁺+0⁺⁺和2⁺⁺(f'₂(1525))+0⁺⁺+2⁺⁺二种三态耦合结构模式,这对于弄清θ(1720)这个宽共振峰的结构,确定可能包含在其中的二个共振态,例如G(1590)和f₂(1720)的质量、宽度、自旋以及其它重要性质,进一步认识这二个令人关注的共振态是有帮助的.     

实验粒子方法应用于核11Li四级软巨共振态的研究

由试验粒子方法求解相空间Vlasov方程,得到核单粒子几率密度分布函数f(r,p,t).基于此研究了核¹¹Li的四极巨共振激发.结果表明,在低激发能区2MeV左右核¹¹Li存在四极软巨共振态,它的强度占E2跃迁能量权重求和(EWSR)的百分比敏感地依赖于¹¹Li核的中子晕分布,而能量中心位于29MeV左右的正常四极巨共振,则与中子晕分布无关.最后对结果作了简要的讨论.     

Gerasimov–Drell–Hearn求和规则的Q2依赖性质

在组分夸克模型中重子共振态的光子激发下,通过数值计算核子上光子总吸收截面σ_1/2和σ_3/2,检验了Gerasimov–Drell–Heam(GDH)求和规则.这种计算包括了总计17个低激发的、非奇异重子共振态.发现纵横相干截面在随Q²变化的求和规则研究中扮演了重要角色.结果显示在94%可信度上这些共振态使GDH求和规则饱和.特别是在Q²=0和小Q²的区域,主要是共振态P₃₃(1232)激发使求和规则饱和.在Q²=1.0GeV²以下,GDH积分有一个很强的Q²依赖性质,且在Q²=0.3GeV²附近变号.由于共振态贡献的迅速下降,当Q²>1.0GeV²时,GDH积分对Q²依赖变弱.     

巨共振激发的相对论效应

在相对论量子场论(QHD)的框架下,得到了相对论线性Vlasov方程.基此计算了球形核¹⁶O、⁴⁰Ca、⁹⁰Zr及²⁰⁸Pb的巨偶极共振的强度函数分布.计算得到的巨共振中心能量,与实验结果比较有较好的符合.对计算结果作了简要的讨论,发现核子有效质量m^*和平均场自旋轨道耦合力对巨共振能量有着重要的效应.     

e+e－实验中ψ(2S)能区连续态单光子湮没过程的贡献

研究了e⁺e^－实验中ψ(2S)能区连续态单光子湮没过程的截面对观测总截面的贡献.针对ψ(2S)质量处ωπ⁰和π⁺π^－两个观测末态,利用唯象模型估计了单光子湮没过程贡献的大小.分析表明,对于ψ(2S)→ωπ⁰和ψ(2S)→π⁺π^－,以及其他电磁末态分支比的确定,单光子湮没过程的贡献必须认真考虑.通过研究,我们认为对于BES实验来说,为了获得共振态电磁末态分支比的正确结果,至少需要在低于ψ(2S)共振峰的能量点采集10pb^－1的数据.     

用相对论Brueckner-Bethe-Goldstone方程研究相对论微观光学位

本文用相对论Brueckner-Bethe-Goldstone(RBBG)方程研究核子-核的相对论微观学学势.核子的复有效质量是通过入射能量为200MeV的质子-⁴⁰Ca散射数据来确定,由此进一步研究了质子对不同靶核:¹⁶O,⁴⁰Ca,⁹⁰Zr,²⁰⁸Pb能量范围从160—800MeV的相对论微观光学位.我们用这种微观光学位研究入射能量为200MeV质子与⁴⁰Ca的弹性散射,并与唯象相对论光学位计算得到的截面,自旋可观测量进行了比较.     

e+e－→τ+τ－,τ－→a1υτ,a1→ρπ过程的角分布和a1介子的性质

给出了过程e⁺e^－→τ⁺τ^－,τ^－→a₁υ_τ,a₁→ρπ的密度矩阵和角分布的螺旋度形式.通过分段拟合把相应于W-a₁跃迁和强作用顶点a₁ρπ形状因子的螺旋度振幅比确定下来,给出了一个确定宽共振态a₁质量和宽度而与模型无关的方法.     

朗之万方程模拟核裂变碎片的同位旋标度

使用结合朗之万方程和统计分支的组合模型模拟¹¹²Sn+¹¹²Sn和¹¹⁶Sn+¹¹⁶Sn两个同位旋相关的反应系统, 通过高斯分布采样的方式得到了核裂变的碎片分布, 将两系统碎片的同位素和同中子异位素的分布相比, 发现存在同位旋标度律现象. 同时提取了同位旋标度系数, 发现同位旋标度系数是和碎片分布宽度相关的, 并且同能量、单位质量的粘滞系数也有很强的依赖关系.     

Resonant Mandelstam-Brillouin light scattering and Raman scattering in semiconductors with intermediate exciton states belonging to discrete exciton bands and the continuous spectrum

The results of a theoretical and experimental investigation of resonant Mandelstam-Brillouin light scattering by thermal acoustic phonons with k=0 near the direct absorption edge (in the case of ZnSe crystals) are analyzed. The appearance of a new type of resonant increase in the intensity of Raman scattering by optical phonons with k≠0, which corresponds to resonance with the scattered light in the output channel, near the indirect absorption edge (in the case of semi-insulating GaP:N crystals) is also reported. The resonant gain reaches ∼4×10³ at frequencies corresponding to overtone scattering assisted by LO(X) and LO(L) phonons. Exciton states belonging to both discrete exciton bands and to the continuous spectrum are considered as the intermediate states involved in the scattering processes in calculations of the resonant scattering tensors. In addition, all the intraband transitions, as well as the interband transitions between the conduction band, the valence bands, and the spin-orbit split-off band are taken into account, and good agreement with the experimental results is obtained. Fiz. Tverd. Tela (St. Petersburg) 40, 938–940 (May 1998)     

Raman spectra of GaAs-AlxGa1-xAs superlattices

Systematic theoretical studies of Raman spectra of GaAs-Al_xGa_1-xAs superlattices are presented. The electronic states are described by an envelope-function method and the phonon modes are described in a microscopic rigid-ion model. Both resonant and nonresonant Raman scattering processes are considered. For resonant Raman scattering, the effects of discrete exciton states plus the continuum and the valence-band mixing are included via a k-space sampling method. Both the Fröhlich and deformation-potential mechanisms for electron-phonon coupling are considered. These two mechanisms are responsible for principal features in the z(x, x)z̄ and z(x, y)z̄ geometries, respectively. We find that the effects of exciton continuum states are quite important and the resonant Raman spectra so obtained are in much better agreement with experiment compared to those without including the exciton continuum states.     

Vector analysing power and cross section for 90Zr(d, p)91Zr at 11 and 12 MeV

Angular distributions of the vector analysing power and the cross section were measured for ⁹⁰Zr($\text{d}$, p)⁹¹Zr. Measurements were made on two transitions at a deuteron energy of 11 MeV and on 20 transitions at 12 MeV. The observed j-dependence of the vector analysing power provided unambiguous spin assignments for most final states. Measurements of the cross section and vector analysing power were also made for deuteron elastic scattering at 11 MeV in order to determine the potential parameters for DWBA calculations. The DWBA predictions are in good agreement with the measured (d, p) cross sections and in qualitative agreement with the analysing powers. Enriched targets.     

Relativistic description of single-particle resonances via phase shift analysis

Single-particle resonant states in spherical nuclei are studied by the real stabilization method in coordinate space within the framework of self-consistent relativistic mean field theory. Taking 122Zr as an example, the resonant parameters, including the energies and widths are extracted by fitting energy and phase shift. Good agreement with the previous calculations has been found. The details of single-particle resonant states are analysed.     

Relativistic description of single-particle resonances via phase shift analysis

Single-particle resonant states in spherical nuclei are studied by the real stabilization method in coordinate space within the framework of self-consistent relativistic mean field theory. Taking 122Zr as an example, the resonant parameters, including the energies and widths are extracted by fitting energy and phase shift. Good agreement with the previous calculations has been found. The details of single-particle resonant states are analysed.     

Comparison of sub-coulomb stripping and analog resonance results in Zr

The ⁹²Zr(d, p)⁹³Zr reaction, leading to states in ⁹³Zr which are parents of analog states observed in ⁹²Zr(p, p) elastic scattering, has been studied for incident deuteron energies below the Coulomb barrier. For each of the parent states the reduced normalization has been extracted, and these have been compared with the reduced normalizations calculated for the analog resonances on the basis of various analog resonance theories.     

Scattering and transfer reactions for 6, 7Li + 90, 91Zr

Elastic scattering data have been measured for the ⁷Li + ⁹⁰Zr, ⁶Li + ⁹⁰Zr, and ⁶Li + ⁹¹Zr systems at E(Li) = 34 MeV. Inelastic scattering data for the ⁷Li + ⁹⁰Zr and ⁶Li + ⁹⁰Zr systems were also measured for the 2⁺(2.18 MeV) and 3^?(2.75 MeV) states in ⁹⁰Zr and the $\text{1}\text{2}{}^{\mathrm{?}}\text{(0.48}\text{MeV}\text{)}$ state in ⁷Li. Optical model analyses of the elastic scattering data and DWBA analyses for the states in ⁹⁰Zr were performed. The deduced deformation lengths for the 2⁺ state agreed with those extracted in other studies but the deformation length for the 3^? state was smaller. The ⁹⁰Zr(⁷Li, ⁶Li)⁹¹Zr angular distributions were measured for the 1.21 and 2.03 MeV states and the 2.19 MeV doublet in ⁹¹Zr. Also, ⁹⁰Zr(⁷Li, ⁶He)⁹¹Nb angular distributions were measured for the ground states, 0.10, 3.41 and 4.82 MeV states in ⁹¹Nb. The transitions well matched in angular momentum were described by finite-range DWBA calculations, while other transitions displayed the same phase problems seen with heavier ions. The extracted spectroscopic information was consistent with the results of other reaction studies. At the present energy, it was not possible to determine whether the l = 1 phase problem that occurs for heavy-ion single-nucleon transfer reactions on 2s-1d shell nuclei occurs in ⁹¹Zr also.     

类钠Ni~(17+)离子双电子复合过程理论研究

使用基于相对论多组态方法的FAC程序,研究了类钠Ni17+(3s)离子通过双激发态Ni16+(3pnl,3dnl)(Δn=0激发)的双电子复合过程,得到了态选择的双电子复合截面和速率系数,并与文献中的实验和理论数据进行了对比.结果发现,计算通过3p3/210l和3p1/211l共振态的双电子复合积分截面在实验误差范围内与实验测量很好地符合,并好于全相对论的多体微扰理论计算结果.结合量子亏损理论,发现包含高里德伯态的共振双激发态的辐射跃迁和自电离速率具有较好的标度关系,利用该关系给出了近激发阈值的所有共振态的双电子复合积分截面和速率系数.比较3pnl和3dnl两个系列,发现在低温(大约小于100eV)等离子体情况下前者速率系数比后者大,更高的温度后者大.     

A mechanism for excitation of metastable levels by(γ,γ') reactions

The analysis of the cross-section of ⁷⁷Se and ⁸⁷Sr isomeric states excitation in the (γ, γ′) reaction, was carried out using neutron pick-up and stripping reaction results. It allows the shell configurations of the transitions to the activation states to be determined. To check thus obtained conclusions the energies of Jπ=1^- excited states for ⁹⁰Zr and ¹³⁸Ba were calculated, which are in good agreement with the resonance structure at the γ-quanta elastic scattering in the 5 to 10 MeV energy range. This revised version was published online in August 2006 with corrections to the Cover Date.