τ衰变中米歇尔(Michel)参数的测量

分析北京谱仪(BES)收集的4.03GeV质心系能量下e⁺e^－对撞数据,选出e⁺e^－→τ^±τ⁺→e^±X⁺v′S事例,X^±可以为μ^±,τ^±,ρ^±,拟合τ→ev′s中电子的能谱,得到τ→ev′s中Michel参数为ρ_τ→e=0.705,此结果与标准模型的预言相符合.     

τ±→π±+nπ0+ντ(n=0,1,2)衰变分支比测量

基于北京谱仪收集的4.03GeV质心系能量下e⁺e^－对撞数据,分析τ^±τ^±→e^±+π^±+nπ⁰+ν's(n=0,1,2)事例,给出分支比值Br(τ^±→π^±ν_τ)=(11.64±0.49^+0.76_－0.73%,Br(τ^±→π^±π⁰ν_τ)=(24.00±1.34^+1.36_－1.30%,Br(τ^±→π^±2π⁰ν_τ)=(9.39±1.68^+1.69_－1.66%.     

7Li2(X1Σ+g)分子的振动能级、转动惯量及离心畸变常数

使用密度泛函理论B3LYP和B3P86，以及组态相互作用方法CCSD(T)和QCISD, 利用多个基组对⁷Li₂(X¹Σ⁺_g)分子的平衡核间距(R_e)、谐振频率(ω_e)和离解能(D_e)进行了计算, 发现在CCSD(T)/cc-PVQZ理论水平下得到的结果(R_{e相似文献}   

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.     

氮化钒的选态双色可见紫外共振增强光电离和脉冲场光电子研究 (cited: 4)

对气态氮化钒(VN)分子在光子总能量为56900～59020 cm^-13∏0, v'=0)的单转动态, 然后再被紫外激光电离．这样的双色激光模式可以测量电子态、振动态和转动态都被选择和解析的氮化钒阳离子VN⁺(X²△; v⁺=0, 1, 2)光谱． 通过对转动解析的PFI-PE光谱模拟分析, 确定J⁺=3/2为基态离子态的最低转动能级, 从而确认VN⁺的基态电子态为²△_3/2．通过对VN+(PFI-PE)光谱的分析得到如下物理量的精确数值：VN⁺(X²△_3/2)的绝热电离能为IE(VN)=56909.5±0.8 cm^-1(7.05588±0.00010 eV),振动常数ω_e⁺=1068.0±0.8 cm^-1,反常振动常数ω_e⁺χ_e⁺=5.8±0.8 cm^-1;VN⁺(X²△_3/2)的转动常数B_e⁺=0.6563±0.0005 cm^-1,α_e⁺=0.0069±0.0004 cm^-1,平衡键长为1.529 ?;VN⁺(X²△_5/2)的转动常数B_e⁺=0.6578±0.0028 cm^-1,α_e⁺=0.0085±0.0028 cm^-1,平衡键长为1.527 ?;X²△_5/2,3/2自旋轨道耦合常数A=153.3±0.8 cm^-1     

BeCl分子电子激发态的多参考组态相互作用计算

运用含Davidson修正的多参考组态相互作用方法,在aug-cc-pVTZ基组水平上,对BeCl分子基态和相同多重度的几个低电子激发态进行了势能扫描计算.通过群论原理确定各电子态对称性及离解极限.将其中基态(X²Σ⁺)和第一激发态(A²Π})对应的势能曲线拟合到Murrell-Sorbie解析势能函数形式,得到基态(X²Σ⁺)的离解能及主要光谱常数(括号中为文献[6]提供的实验值)为D_e=3.74eV,R_e=0.18173nm(0.17970),w_e=857.4cm¹(847.2),w_ex_e=5.03cm^-1(5.14),B_e=0.7103cm^-1(0.7285),α_e=0.0059cm^-1(0.0069),第一激发态(A²Π)的D_e=3.02eV,R_e=0.18369nm(0.18211),w_e=832.7cm^-1(822.1),w_ex_e=5.93cm^-1(5.24),B_e=0.6953cm^-1(0.7094),α_e=0.0065cm^-1(0.0068),计算结果与实验值符合得较好.另外,通过Level程序求解双原子径向核运动的Schrödinger方程得到J=0时BeCl分子这两个电子态的全部振动能级.     

Ds衰变常数的测量

利用北京谱仪在e⁺e^－对撞质心能量4.03GeV所取得的约22.3pb^－1的数据,用先标记μ,后标记D_s的方法,共找到2个D_s→μv,3个D_s→τv→μvvv衰变候选事例,给出了D_s的纯轻子衰变的绝对分支比为:Br(D_s→μv)+0.72+0.70－0.44),Br(D_s→τv)=(14+11－8)%,并给出不依赖于模型假设的D_s衰变常数为:f_Ds=(355+96+28－90－28)MeV.     

最小Higgs模型在ILC上可能的味改变物理迹象

在最小Higgs(LH)模型中, 由于引进了类矢量顶夸克T, 对弱作用流产生了新的影响. CKM矩阵从3×3变为4×3, 在树图下出现味改变中性流(FCNC). 本文研究了在国际高能直线对撞机(ILC)上能否通过e⁺e^－→tc+tc和e⁺e^－→WWν_eν_e→(tc+tc) ν_eν_e过程探测到LH模型所预言的FCNC信号.     

PuO分子X5Σ-态的势能函数及热力学 函数的量子力学计算

The potential energy function for ground state X⁵Σ^- of the PuO molecule was worked out by the quadratic configuration interaction of single and double substitution method, based on the approximation of relativistic effective core potential for Pu atom and all-electron 6-311G^ basis set for O atom. The calculated results for R_e,D_e,B_e,α_e,ω_e and ω_eχ_e are 0.183nm,7.3909eV,0.3365,0.001642,781.15,and 2.77cm^-1,respectively.In addition,the thermodynamic functions ΔH⁰,ΔS⁰,ΔG⁰ and C_p of the PuO(g) in standard state are also calculated,which are -118.88kJ/mol,96.16J/mol^.K,-147.55kJ/mol,and 31.5656J/mol^.K,respectively. All these results are in good agreement with the experimental data.     

高能正负电子对的湮没与超窄共振ψ粒子的作用

本文给出了R=(σ(e⁺e^-→强子))/(σ(e⁺e^-→μ⁺μ^-))随能量上涨的一个解释。研究了新发现ψ粒子所具有作用的性质,指出其强度f²/(4π)～10^-5—10^-6。求得峰值截面σ₀=(12π)/m_ψ²(Γ(ψ→e⁺e     

混响强度及其衰减规律与脉宽的关系

本文由短脉宽下混响强度的普遍表达式I_r(t,τ)=Kτt^-me^-βt出发,导出对应的可用于长脉宽的混响强度精确表达式,并给出了忽略脉宽尺度范围的指数衰减损失后相应的近似表达式。当指数衰减系数β足够小和脉宽大于有效脉宽τ_m=a_mt(a_m随m增大而减小,m是大于2的实数)时,近程混响强度趋向饱和且随时间t的(m-1)次幂衰减。实验结果与理论符合较好。     

Results from the NOMAD experiment

The NOMAD experiment has sought ν_μ ? ν_τ oscillations by looking for the emergence of τ^? in events from the CERN SPS neutrino beam. With some improvements in the techniques of analysis in relation to the results published previously and with the inclusion of data from the 1998 run, no evidence for the oscillations has been found, which results in an updated limit on the oscillation probability [P(ν_μ → ν_τ) < 0.5 × 10^?3 at a 90% C.L.]. The corresponding limit on the oscillation mixing angle is given by sin²2θ_μτ < 1.0 × 10^?3 for large Δm ². By using a 1% contamination of ν_e in the neutrino beam, we can also rule out ν _e ? ν_τ oscillations and constrain the probability of the relevant transition as P(ν _e → ν_τ) < 3 × 10^?2 at a 90% C.L. (sin²2θ _eτ < 6 × 10^?2 at large Δm ²).     

YBa2Cu3O7超导管内磁场与外磁场的关系

本文报道了当外磁场H_e较低时(H_e<4H_rm,其中H_rm是超导管的最大捕获磁场),超导管的内磁场H_i与时间及外磁场的关系可表示为H₀+B₀(lnt+1-exp(-t/τ)),式中B₀Int与磁通蠕动有关,B_c(1-exp(-t/τ))与外磁场引起的磁通扰动有关。扰动随时间很快衰减.H₀,B₀及1/τ随外磁场增加,在H_e>H_rm时,这几个量增加较大。当直流外磁场H_e<1/2H_rm时,超导管可将其完全屏蔽,对交流场不能完全屏蔽,但其屏蔽效果仍优于最好的金属屏蔽筒。 关键词：     

Orientierung nematischer Phasen im Magnetfeld

Orientation of Nematic Phases in Magnetic Fields We discuss two methods to measure the reorientation times τ_0r of the director in nematic phases of liquid crystals in an external magnetic field. Both methods give the same results; advantages and disadvantages are considered. It appears that the relation resulting from continuum theory tan Φ ∞e^?t/τ0r is fulfilled (Φ twist angle). In the appendix we discuss optimum conditions for the pulse method.     

Neutral hydrogen-like system in a magnetic field

Explicit formulae are derived relating the energies and the ionisation potentials of an arbitrary neutral two-particle system in a magnetic field B to the energies and the ionisation potentials of a hydrogen atom of infinite nuclear mass in a magnetic field (m_e/μ)²B.     

Observation of possible production and decay of short-living heavy neutral particles in the SKAT neutrino experiment

In the SKAT bubble chamber neutrino experiment production of a short-living neutral particle with mass (1.4?m?2.5) GeV/c² and lifetime τ≈6×10^?12 s has been detected. The event may be interpreted as production and decay of the heavy lepton M⁰→μ^?+e⁺+ν_e with mass (1.4?m_M⁰?2.1) GeV/c². It might also be the production of a charmed particle D⁰→e⁺+τ^?+ν_e (D⁰→e⁺+π^?+ν_e) with mass 1.4?m_D⁰?2.5) GeV/c² in a non-diagonal neutral current. The probability to interpret the event as other possible processes is very low.     

On the Symmetrical Modes in a Cylindrical Nonisothermal Plasma Waveguide in a Finite External Magnetic Field

A MHD, symmetrical, nonpotential waves in nonuniform, cylindrical nonisothermal plasma waveguide placed in a finite external magnetic field H ₀ directed along the axis of the waveguide are considered. The thermal velocity of the electrons ν_Te = (kT_e/m_e)^1/2 (k — Boltzman's constant, T_e — temperature, m_e — mass of the electron) is not neglected. As a consequence we obtain one more solution in the plasma region and respectively an equation of third power on χ² — the transverse wave number. As far as we know only equations of second power on χ² describing non-potential waves are investigated. The dispersion equations are written solving the boundary-value problem. Our results coincide with well known ones when the electron thermal velocity tends to zero.     

Limits on the τ neutrino electromagnetic properties from single photon searches ate + e − colliders

We set limits on the magnetic moment and charge radius of the τ neutrino by examining the contributions to the processe ⁺ e ^?→v \(\bar \nu \) γ due to such interactions. We find thatK(ν_τ)<4×10^?6 (i.e.μ(ν_τ)<4×10^?6μ _B , μ _B =e/2m _e ) and 〈r ²〉<2×10^?31 cm² using the combined data of the MAC, ASP, CELLO, and Mark J collaborations for this process. We briefly discuss whether these bounds can be improved in any futuree ⁺ e ^? experiments.     

Spin-flip scattering effect on the current-induced spin torque in ferromagnet–insulator–ferromagnet tunnel junctions

We have investigated the current-induced spin transfer torque of a ferromagnet–insulator–ferromagnet tunnel junction by taking the spin-flip scatterings into account. It is found that the spin-flip scattering can induce an additional spin torque, enhancing the maximum of the spin torque and giving rise to an angular shift compared to the case when the spin-flip scatterings are neglected. The effects of the molecular fields of the left and right ferromagnets on the spin torque are also studied. It is found that τ^Rx/I_e (τ^Rx is the spin-transfer torque acting on the right ferromagnet and I_e is the tunneling electrical current) does vary with the molecular fields. At two certain angles, τ^Rx/I_e is independent of the molecular field of the right ferromagnet, resulting in two crossing points in the curve of τ^Rx/I_e versus the relevant orientation for different molecular fields.     

Spontaneous Symmetry Breaking in Presence of Electric and Magnetic Charges

Starting with the definition of quaternion gauge theory, we have undertaken the study of SU(2) _e ×SU(2) _m ×U(1) _e ×U(1) _m in terms of the simultaneous existence of electric and magnetic charges along with their Yang-Mills counterparts. As such, we have developed the gauge theory in terms of four coupling constants associated with four-gauge symmetry SU(2) _e ×SU(2) _m ×U(1) _e ×U(1) _m . Accordingly, we have made an attempt to obtain the abelian and non-Abelian gauge structures for the particles carrying simultaneously the electric and magnetic charges (namely dyons). Starting from the Lagrangian density of two SU(2)×U(1) gauge theories responsible for the existence of electric and magnetic charges, we have discussed the consistent theory of spontaneous symmetry breaking and Higgs mechanism in order to generate the masses. From the symmetry breaking, we have generated the two electromagnetic fields, the two massive vector W ^± and Z ⁰ bosons fields and the Higgs scalar fields.