Decay Pion Spectroscopy of Electro-Produced Hypernuclei

The investigation of light hypernuclei is quite important for understanding the basic YN interaction and the mechanism of hypernuclear structure. We started the commissioning of the decay pion spectroscopy of light hypernuclei at MAMI-C in 2011. In order to realize the K⁺ tagging efficiently, some detectors on KAOS spectrometer were upgraded or newly installed. The existing and well-studied spectrometers, SpekA, SpekC were used as pion spectrometers. The analysis is ongoing to estimate the detectors performance and develop the spectrometers for future experiments with higher beam intensity. The preliminary results of the particle identification are presented in this article.     

Electro-Production of Light Lambda Hypernuclei

Through the study of light hypernuclei, we can learn about hyperon nucleon interaction. The hypernuclear spectroscopy with electron beams is one of most powerful methods to study detailed structure of light hypernuclei thanks to its high energy resolution. With a decade of efforts at Jefferson Lab, the spectroscopy of Λ hypernuclei with an electron beam is now established. Observation of ${_{\Lambda}^{7}}$ He which gave the last missing binding energy of the A = 7, T = 1 iso-triplet hypernuclei provides an important experimental input for the charge symmetry breaking (CSB) effect of the ΛN interaction. Further study about A = 4 hypernuclear iso-doublet, ${_{\Lambda}^{4}}$ H and ${_{\Lambda}^{4}}$ He, is necessary and such experiments are now planned.     

Weakly Bound States in Light Hypernuclei

From the viewpoint of critical stability, we discuss the three- and four-body structure of ⁶He, ⁷He, ⁴He, and ⁴H. With the + + N three-body model, ⁶He is found to have a three-layer structure of the matter distribution: core, a skin and neutron halo. Also the level structure of ⁷He with the three-body model of ⁵He + n + n is predicted. This stimulates a new study of neutron-rich and proton-rich hypernuclei. By performing a four-body calculation with both NNN and NNN channels and with both NN and NNN channels, we show that the N-N and -N couplings are very important in critical stability of few-body hypernuclear systems.     

Three- and Four-body Structure of Light Hypernuclei

Hypernuclear physics has become very exciting owing to new epoch-making experimental data.Recent progress in theoretical and experimental studies of hypernuclei and future developments in this field are discussed.     

Light Hypernuclei Based on Chiral Interactions at Next-to-Leading Order

We present predictions for the binding energies of the light hypernuclei \({^3_\Lambda{\rm H},\, ^4_\Lambda{\rm He}}\) and \({^4_\Lambda{\rm H}}\) based on Faddeev- and Yakubovsky equations in momentum space. We discuss how such results can help to test the existing hyperon–nucleon (Y N) potential models and effective field theory based Y N interactions. Especially, we show results for the chiral interactions at next-to-leading order.     

≡ Hypernuclei

We consider the possibility of forming doubly strange Ξ hypernuclei via the (K^?, K) reactions on various nuclear targets. Because of the high momentum transfer involved, even at 0°, the formation of high spin states is strongly favored. The available experimental information on the elementary processes K^?p → K⁺Ξ^? or K⁰Ξ⁰ is reviewed, leading to the determination of an optimum incident K^? momentum of about 1.9 GeV/c for the forward formation of discrete Ξ hypernuclear states. The cross section for the process ΞN → ΛΛ, responsible for the damping width of Ξ states in nuclei, is estimated theoretically and the very limited experimental data are also reviewed. The resulting Ξ hypernuclear widths are of order 5 MeV. Emulsion data which have been interpreted as due to the existence of ΛΛ and Ξ^? hypernuclei are discussed and used to obtain an approximate Ξ nuclear well-depth of 21–24 MeV. For this range of values, spectra of single particle Ξ^? states are obtained, and calculated angular distributions for the formation of simple Ξ^? particle-proton hole states in ⁴He, ¹²C and ²⁸Si targets are presented. The peak 0° lab cross section at p_lab = 1.9 GeV/c for such states ranges from tens of $\text{nb}\text{sr}$ to about 1 $\text{μ}\text{b}\text{sr}$. We briefly mention other methods for forming Ξ hypernuclei, such as the three body reaction K^?N → KπΞ (or $\text{K}{}^{\mathrm{?}}\text{p → K}{}^{\mathrm{+}}\text{K}{}^0\text{Ω}{}^{\mathrm{?}}$ for $\text{Ω}{}^{\mathrm{?}}$ hypernuclei).     

卤化银微晶中光电子衰减谱的特性

光电子在卤化银材料潜影形成过程中发挥着重要的作用 ,光电子衰减行为在很大程度上决定于卤化银的晶体结构。采用光学与微波双共振技术 ,测量了自由光电子和浅俘获光电子的衰减谱 ,得到了卤化银中电子陷阱的密度和深度分布。以自由光电子寿命为纽带 ,通过分析掺杂卤化银晶体中电子陷阱的分布情况 ,可以确定浅电子陷阱掺杂剂的最佳掺杂浓度。     

Hypernuclei and baryon-baryon interaction

A central ΛN potential containing spin and charge dependences is constructed on the basis of an analysis of fundamental hypernuclear data (Λp scattering, the binding energies of the ground and excited states of hypernuclei). The lightest hypernuclei ( _Λ ³ H, _Λ ⁴ H, _Λ ⁴ He) are calculated as a system of three or four particles on the basis of the highly efficient variational method. Heavier hypernuclei are considered in terms of a twobody model (Λ + undeformed nucleon core) corrected by comparison with direct 3–5-particle calculations. By comparing the results of the calculations of single and double Λ hypernuclei and taking the considerations of meson theory into account, it is possible to estimate the binding energies of charmed and other (b- and t-quark) supernuclei. M. V. Lomonosov State University, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 19–27, October, 1997.     

Hypernuclei with sigma particles

The production of Σ particles in the (K⁻, π⁻) on ⁹Be at 720 MeV/c has been studied at the CERN proton synchrotron (PS). The missing-mass spectrum shows structures in the Σ region, which have been interpreted as belonging to hypernuclei with sigma particles. An upper limit of 8 MeV for the width of these states has been estimated.     

Decay of Weak Solutions to the 2D Dissipative Quasi-Geostrophic Equation

We address the decay of the norm of weak solutions to the 2D dissipative quasi-geostrophic equation. When the initial data θ₀ is in L ² only, we prove that the L ² norm tends to zero but with no uniform rate, that is, there are solutions with arbitrarily slow decay. For θ₀ in L ^p ∩ L ², with 1 ≤ p < 2, we are able to obtain a uniform decay rate in L ². We also prove that when the norm of θ₀ is small enough, the L ^q norms, for , have uniform decay rates. This result allows us to prove decay for the L ^q norms, for , when θ₀ is in . The second author was partially supported by NSF grant DMS-0600692.     

Hypernuclei and in-medium chiral dynamics

A recently introduced relativistic nuclear energy density functional, constrained by features of low-energy QCD, is extended to describe the structure of hypernuclei. The density-dependent mean field and the spin-orbit potential of a Λ-hyperon in a nucleus, are consistently calculated using the SU(3) extension of in-medium chiral perturbation theory. The leading long-range ΛN interaction arises from kaon-exchange and 2π-exchange with a Σ-hyperon in the intermediate state. Scalar and vector mean fields, originating from in-medium changes of the quark condensates, produce a sizeable short-range spin-orbit interaction. The model, when applied to oxygen as a test case, provides a natural explanation for the smallness of the effective Λ spin-orbit potential: an almost complete cancellation between the background contributions (scalar and vector) and the long-range terms generated by two-pion exchange.     

Absolutely Continuous Spectra of Quantum Tree Graphs with Weak Disorder

We consider the Laplacian on a rooted metric tree graph with branching number K≥2 and random edge lengths given by independent and identically distributed bounded variables. Our main result is the stability of the absolutely continuous spectrum for weak disorder. A useful tool in the discussion is a function which expresses a directional transmission amplitude to infinity and forms a generalization of the Weyl-Titchmarsh function to trees. The proof of the main result rests on upper bounds on the range of fluctuations of this quantity in the limit of weak disorder.     

Study about Light Hypernuclei and YN Interaction Based on Chiral SU(3) Quark Model

In terms of the YN interaction based on the chiral SU(3) quark model,the spectra of light hypernuclei 4ΛH,4ΛHe and 5ΛHe are calculated. The result shows that the effective local ΛN potential,as an approximation,cannot offer a reasonable explanation of the empirical data, while the non-local ΛN potential,also as an approximation,can provide a reasonable range of the binding energy of 5ΛHe and correct ordering of the energy levers of 4ΛH,4ΛHe. This indicates that the non-local character of the effective YN interaction plays an important role in binding behavior. The upper bounds and lower bounds of energy levels are given by employing two sets of model parameters in the calculation. Thus,the experimental data of hypernuclei can provide more information as the constraints of model. In the present stage,YN interaction(no matter phenomenology of theoretical interaction) cannot be finalized due to lack of experimental data. Utilizing experimental data,it is possible to optimize model parameters in the theoretical studies of YN interaction.     

基于手征SU(3)夸克集团模型的YN相互作用和轻超核研究

采用基于手征SU(3)夸克集团模型的YN相互作用位,计算了轻Λ超核5ΛHe,4ΛHe和4ΛH的能谱.结果显示,近似的等效定域ΛN相互作用位不能给出正确的超核结合能,而非定域ΛN位能给出超核5ΛHe结合能的合理范围以及超核4ΛHe和4ΛH能级的正确顺序.这表明YN相互作用的非定域性起着重要的作用.计算中采用了2套模型参数,计算结果正好给出实验值的上下限.这表明超核的实验数据可以提供更多的信息来进一步约束YN相互作用,以弥补YN散射实验数据的不足.利用超核实验数据来优化选择YN相互作用参数是有可能做得到的.     

超核γ谱学研究进展

近年来 ,在7ΛLi超核γ谱学实验中 ,通过基态二重态间自旋翻转M1跃迁能量的测定 ,为ΛN自旋 自旋相互作用强度提供了重要的信息 ;通过对约化跃迁几率B(E2 ;7ΛLi 5 / 2 + → 1/ 2 + )的测定 ,表明7ΛLi中的6Li核心比自由空间中6Li核要小 ,Λ超子的胶样作用引起了7ΛLi核的收缩 . The recent progress in gamma-ray spectroscopy of hypernuclei is described. The spin-flip M1 γ transition between the ground-state spin doublet of 7 ΛLi has been observed. The transition energy provides crucial information on the strength of the spin-spin intetraction between Λ and nucleons. The experimental result of B(E2; 7 ΛLi 5/2 +→1/2 +) gives evidence that the size of the 6Li core in 7 ΛLi is smaller than that for the 6Li nucleus in the free space, indicating that the...     

Effective Flavor-changing Weak Neutral Current in the Standard Theory and Z-Boson Decay

We have studied the effective Zf ₁f₂-vertex in the Glashow-Salam-Weinberg theory arising from 1-loop corrections, allowing for arbitrary fermion masses m_i in the loop. We use our results to study the branching ratio of the Z-boson decay into two different fermions. This is of phenomenological interest if there exist yet unknown fermions with large mass which could show up at present and designed accelerators only through radiative corrections.     

奇特核和超核中的晕现象

讨论奇特核和超核中的各种晕现象. 根据密度相关零程对力的相对论连续谱Hartree Bogoliubov理论给出的计算结果， 预言了中子滴线附近的Ca原子核中可能存在着巨晕， 并简要介绍了O， Ni， Zr， Sn和Pb等一些质子幻数核从质子滴线到中子滴线之间的原子核基态性质. 随后给出超核内的晕现象研究， 如Ca超核内的中子晕和153ΛC内的单Λ超子晕. Halos in the relativistic continuum Hartree Bogoliubov (RCHB) theory are investigated，including giant halo in the even N Ca isotope near neutron drip line，halos in hypernuclei and the hyperon halos in 153ΛC.     

极微弱脉冲光强度稳定控制技术

实际测量输出光强度随时间变化的随机过程是一个慢过程.将光衰减过程分为固定衰减和可变衰减两部分,设计制作了一种实时监控系统,通过调节自动反馈控制可变衰减器,使得末端固定衰减器的输出脉冲中,单光子脉冲出现的概率等于17.6%,多光子脉冲出现的概率低于2%,保持平均光子输出速率波动不大于0.1%,为量子密码术提供了稳定的准单光子源.