自旋相关的Λ超子与核子间张量相互作用的首次观测

超核γ谱学国际合作组在用超球γ谱仪(Hyperball)进行的1Λ6O的γ射线谱学测量中,观察到由1Λ6O的6.6MeV12-激发态跃迁到基态自旋翻转二重态(11-和0-)之间的两条γ射线.由这两条γ射线的能量差得到基态二重态之间的能量间隔为26.4±1.6(统计误差)±0.5(系统误差)keV,并由此推导出ΛN之间的张量相互作用强度T=0.03MeV.实验还测定了Λ16O的12-激发态的激发能为6561.7±1.1(统计误差)±1.7(系统误差)keV.     

ΛN张量相互作用的首次观测

在用HYPERBALL进行的16ΛO的γ射线谱学测量中, 观察到由16ΛO的6.6 MeV 1－2 激发态跃迁到基态自旋翻转二重态( 1－1和0-)之间的两条γ射线. 由这两条γ射线的能量差得到基态二重态之间的能量间隔为26.4 ± 1.6(stat) ± 0.5(syst) keV, 并由此推导出ΛN之间的张量相互作用强度T=0.03MeV.实验还测定了16ΛO的激发态的激发能为6561.7 ± 1.1(stat) ± 1.7(syst) keV.     

相对论平均场理论中的有效超子-核子相互作用

利用相对论平均场理论,结合单超核的实验数据,研究了核介质中的Λ超子–核子有效相互作用.通过符合13ΛC超核中Λ超子1s轨道的结合能实验值,给出了5组Λ超子–核子有效相互作用参数.利用这些参数组对质量数从9到2?0?8的单Λ超核和核物质中最低Λ态的束缚能进行了系统计算,得到的结果与实验值相符.     

稀土区变形核十六极矩与核子间的相互作用

本文采用区分质子和中子的BCS方法,用尽量少的参数计算了整个希土区偶-偶核的十六极矩Q₄₀与四极矩Q₂₀值,部分结果与实验有较好的符合.实验与理论计算的结果还表明,同种核子间的四极相互作用强度仅为质子、中子间四极相互作用的五分之一,但对于解释Q₄₀的规律是十分重要的.     

张量相互作用对核子和反核子束缚态的效应

由于量子真空对密度的贡献,在有限核的相对论Hartree模型中核子有效质量为0.8M_N左右,导致自旋轨道力仅是实验值的三分之一,本文通过引入矢量介子的张量耦合项,使自旋轨道力增加了一倍,同时保持有效质量不变,相应的核子能谱与实验值的符合得到明显改进,而预言的真空反核子位阱深度增大了20—30MeV.     

核形变随Z,N的变化与核子间相互作用的电荷无关性

用双能级模型以及与电荷无关的核子-核子相互作用研究核形变随Z,N的变化,得到了与实验大体相符的结果.     

Ξ超子-核子有效相互作用Skyrme力参数的初步研究

在SkyrmeHartreeFock理论框架下,根据已有实验数据首次对ΞN有效相互作用进行了研究,初步确定了ΞN的Skyrme有效力参数,并由此计算了几种Ξ超核的势阱深度和相应的Ξ超子单粒子能级,以及Ξ超子在核中的均方根半径和相应超核的电荷分布半径,在较大的范围内得到了合理的结果.     

First direct observation of strong interaction spin-orbit effects in antiprotonic atoms

The strong ¯p-nucleus spin-orbit interaction was investigated in a measurement of the strong-interaction effects of the 9→8 transition in ¯p ¹⁷⁴Yb at the Low-Energy Antiproton Ring (LEAR) at CERN. This measurement was part of an experimental programme where, for the first time, the fine-structure components of the last observable X-ray transition in a ¯p atom, which carries information on the strong ¯p-nucleus interaction, were resolved and studied individually. The observed splitting ΔE _exp=2408±26 eV consists of the electromagnetic fine-structure splitting ΔE _FS=2350 eV and an additional splitting Δ?=58±26 eV. In addition, one finds a significant difference in the level widths of Δ=195±59 eV with the larger value_?=1216±41 eV for the lower fine-structure level. This experiment follows an earlier measurement on ¯p ¹³⁸Ba, where the transition 8→7 is influenced by the strong interaction. In this case, however, the fine-structure components could not be resolved. The results for¹⁷⁴Yb may be attributed to a spin-orbit (LS) term in the complex strong-interaction potential.     

Shell structure fingerprints of tensor interaction

We address the consequences of strong tensor terms in the local energy density functional, resulting from fits to the f _5/2 -f _7/2 splittings in ⁴⁰Ca , ⁴⁸Ca , and ⁵⁶Ni . In this study, we focus on the tensor contribution to the nuclear binding energy. In particular, we show that it exhibits an interesting topological feature closely resembling that of the shell correction. We demonstrate that in the extreme single-particle scenario at spherical shape, the tensor contribution shows tensorial magic numbers equal to N(Z) = 14 , 32, 56, and 90, and that this structure is smeared out due to configuration mixing caused by pairing correlations and migration of proton/neutron sub-shells with neutron/proton shell filling. Based on a specific Skyrme-type functional SLy4_T, we show that the proton tensorial magic numbers shift with increasing neutron excess to Z = 14 , 28, and 50.     

First observation of the Greisen-Zatsepin-Kuzmin suppression

The High Resolution Fly's Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes' measurement of the flux of ultrahigh energy cosmic rays shows a sharp suppression at an energy of 6 x 10(19) eV, consistent with the expected cutoff energy. We observe the ankle of the cosmic-ray energy spectrum as well, at an energy of 4 x 10(18) eV. We describe the experiment, data collection, and analysis and estimate the systematic uncertainties. The results are presented and the calculation of the statistical significance of our observation is described.     

Search for tensor couplings in the weak interaction

The existence of exotic couplings in the weak interaction can be tested by a precise measurement of the β-ν angular correlation parameter a in nuclear beta decay. In the case of ⁶He, the ratio of tensor and axial-vector couplings can be determined. The goal of the LPC Trap experiment is to improve the limits on the existence of tensor currents. The LPCTrap setup is installed on the low energy beam line LIRAT of the SPIRAL/GANIL facility. The ⁶He⁺ ions are confined in a novel transparent Paul trap allowing the detection in coincidence of both the β-particle and the recoil ion. The detection setup enables to detect the position and energy of these two particles. The a parameter can then be extracted from the time of flight spectrum of the recoil ions. The first ⁶He⁺ decay events were observed in May 2005 during a commissioning run. Over 10⁵ coincidence events have been recorded during a second run in July 2006.     

First observation of F

We measured the excitation function for ¹³O + p elastic scattering to obtain data on the unknown ¹⁴F nucleus. The ground state and several low-lying excited states in ¹⁴F were observed and spin/parity assignments were made. ¹⁴F appears to be much less unstable than was predicted. We compare theoretical predictions for the ¹⁴F level scheme with the experimental results.     

The tensor interaction and nuclear matter

The separation method of Moszkowski-Scott has been applied to the calculation of the properties of nuclear matter using two different nucleon-nucleon potentials, both in reasonable agreement with two-body data. Calculations with the potential of Brueckner-Gammel gave $\text{A}\text{E}\text{= ?14.2}\text{Mev}$ at an equilibrium densitty corresponding to k_f = 1.5 f^?1. The difference from the results of B and G may be caused by slow convergence of the series (especially in the triplet-even state where the tensor interaction has a large second order contribution). An important factor in obtaining nuclear saturation is shown to be the weakening of tensor interaction effects by the Fermi sea. Evidence for this may also be seen from the results obtained using a different two nucleon potential which, however, still gives good fits to two body data. The potential chosen has a much weaker tensor component and shows no sign of saturation at normal densities (at k_f = 1.5 f^?1, $\text{A}\text{E}\text{= ?23.4}\text{Mev}$). The difference in the two results appears to be much larger than can be accounted for either by higher order terms or by differences in the phase shift approximation to the reaction matrix.     

First observation of electrorheological plasmas

We report the experimental discovery of "electrorheological (ER) complex plasmas," where the control of the interparticle interaction by an externally applied electric field is due to distortion of the Debye spheres that surround microparticles (dust) in a plasma. We show that interactions in ER plasmas under weak ac fields are mathematically equivalent to those in conventional ER fluids. Microgravity experiments, as well as molecular dynamics simulations, show a phase transition from an isotropic to an anisotropic (string) plasma state as the electric field is increased.     

On a tensor force addition to the modified surface-delta interaction

A potential consisting of the modified surface-delta interaction plus a tensor force is fitted to the 15 empirical two-body matrix elements of the upper s-d shell and, independently, to 12 two-body matrix elements of the shells.