Hypernuclear physics

The contributed papers submitted to the session C Hypernuclear and kaon physics and not presented orally at the Conference are briefly reviewed here.Rapporteur talk at the symposium Mesons and Light Nuclei IV, Bechyn, Czechoslovakia September 5–10, 1988.     

Hypernuclear spectroscopy

Conclusions The main difference between the- nucleus and the nucleon-nucleus interaction is in the spin dependence. The spin-spin and spin-orbit interaction is an order of magnitude weaker for the-nucleus than for the nucleon-nucleus system. If we want to emphasize the difference between hypernuclei and nuclei in an oversimplifying manner, we may say that the particle in the nucleus behaves like a spinless neutron.This radical difference in the behaviour of particles and nucleons in nuclear matter presents a sensitive test for the models of nuclear matter. Hypernuclear spectroscopy if studied in detail, a program just begun, promises to give valuable information on the effective properties of the quasiparticles in the nucleus and their interactions, both basic ingredients of nuclear models.Rather surprisingly, hypernuclei live long enough to observe individual states, as can be deduced from the berylium results. These results should be verified as soon as possible. If they are confirmed, this will challenge experimentalists to determine the -nucleus interaction in the same way as done for particles and the theorists to explain why the strong decay of particles in the nucleus is hindered.Invited talk at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.     

Hypernuclear photoproduction

Calculations of the nuclear (γ, K⁺) reaction employing full Coulomb and optical distortions and a complete photoproduction vertex are reported. Hypernuclear excitations other than spin-flip modes are found to be significantly excited and distortion effects are found to strongly alter the magnitude of the cross sections.     

Entropy production per site in (nonreversible) spin-flip processes

Entropy production per site in a (nonreversible) spin-flip process is studied. We give it a useful expression, from which a property stronger than affinity of the entropy production per site follows. Furthermore, quasi-invariance of nonequilibrium measures in the spin-flip processes is discussed via entropy production.     

Thermospin effects in a T-shaped spin valves with spin-flip scattering

With the help of the nonequilibrium Green's function technique, we theoretically analyze the thermospin property through a typical T-shaped spin valve with spin-flip scattering in the linear regime. The influences of spin-flip coefficient of interdot λ, spin-flip coefficient of intradot η and interdot hopping coefficient $t+{\delta }_{\sigma }\mathrm{\Delta }t$ on thermospin property are discussed. As interdot hopping coefficient t is equal to energy level ε, the spectrum of $G_s$ shows Fano-like effect with ε variation. Antiresonance position of $G_s$ is almost unchanged and its width becomes narrower with ε increasing. Spin thermopower $S_s$ is close to the maximum of the peak and charge thermopower $S_c$ is equal to zero for $t=\epsilon$. As a result, the pure spin thermopower $S_s$ can be obtained, which means that a pure spin current may be produced by a temperature gradient in our system. It is found that spin figure of merit $Z{T}_s$ can reach a considerable value by adjusting key parameters of the system, such as Δt, β, α, ?. The typical T-shaped spin valve can be treated as a stable thermospin battery which allows to convert the heat energy to spin voltage, thus produces the pure spin current in the device.     

Multiline output from a spin-flip laser

Multiplicity of the output frequency of a spin-flip laser, caused by the simultaneous multiline operation of the CO pump laser, is identified. This multiplicity is shown to arise from a four-wave mixing process for which only a single input threshold intensity exists for oscillation. Experimental data are presented together with a determination of the interdependence of the input and output frequency power ratio.     

超核物理学进展

简要评述超核物理学近几年的发展,包括常规超核和非常规超核两个方面.对于包含通常超子的常规超核,重点介绍近来在日本KEK完成的一批超核实验及其理论分析.对其中关于超子杂质效应和超子平均自由路程等实验测量结果进行了理论分析,得到一些有意义的结果.并对奇异数为S=-2的Ξ超核的结构和性质进行了若干研究.对于包含C夸克或B夸克的其他味超核,以及可能的包含pentaquark的θ+超核也做了适当的介绍. Progress and recent status of experimental and theoretical investigations on hypernuclear physics are briefly reviewed, including conventional hypernuclear physics and unconventional hypernuclear physics. We introduce the recent progress of hypernuclear experiments in KEK, Japan and the studies of fine structure in γ-ray spectroscopy of Λ hypernuclei. The spin-flip transition between the ground-state spin doublet of light hypernuclei has been observed and the transition energy provides important..     

Plasma production and thermalisation in a strong field

Aspects of the formation and equilibration of a quark–gluon plasma are explored using a quantum kinetic equation, which involves a non-Markovian, Abelian source term for quark and antiquark production and, for the collision term, a relaxation time approximation that defines a time-dependent quasi-equilibrium temperature and collective velocity. The strong Abelian field is determined via the simultaneous solution of Maxwell's equation. A particular feature of this approach is the appearance of plasma oscillations in all thermodynamic observables. Their presence can lead to a sharp increase in the time-integrated dilepton yield, although a rapid expansion of the plasma may eliminate this signal. Received: 27 July 2001 / Published online: 21 November 2001     

Hypernuclear spectroscopy in the p shell

A comprehensive shell-model approach to Λ-hypernuclear spectroscopy in the p shell is developed. The available data on the spectra of ⁹_ΛBe, ¹²_ΛC, ¹³_ΛC, ¹⁴_ΛN and ¹⁶_ΛO are interpreted in this framework, leading to constraints on the residual ΛN interaction and the one-body Λ-nucleus potential. The mechanism for the formation of Λ hypernuclei via the (K^?, π^?) reaction is treated in the relativistic distorted wave approximation, with careful attention paid to Fermi-averaging of the elementary K^?n → π^?Λ amplitude and recoil corrections. Departures from the simple weak coupling picture, arising from configuration mixing, are emphasized. This leads to approximate dynamical symmetries in hypernuclei which are forbidden in ordinary nuclei by the Pauli principle. Further experiments in the p shell are suggested which may reveal other aspects of ΛN interactions.     

Recent Achievements in Hypernuclear Physics

In the last decade the hypernuclear physics community was committed to carrying on several third-generation experiments. Large data samples were collected on specific items, thanks to dedicated facilities and experimental apparatuses. The attention was focused on both high-resolution spectroscopy and decay mode study of single Λ-hypernuclei. Nowadays this phase is over but, until recently, important and to some extent unexpected results were achieved. Among others, the claim for the first observation of the neutron-rich hypernucleus \({^6_\Lambda{\rm H}}\) and the first experimental evidence for the hypernucleus two-nucleon induced weak decay raised strong interest.     

Few-Body Aspects of Hypernuclear Physics

Recent development in the study of the structure of light Λ and double Λ hypernuclei is reviewed from the view point of few-body problems and interactions between the constituent particles. In the study the present author and collaborators employed Gaussian expansion method for few-body calculations; the method has been applied to many kinds of few-body systems in the fields of nuclear physics and exotic atomic/molecular physics. We reviewed the following subjects studied using the method: (1) Precise three- and four-body calculations of ${^7_{\Lambda}{\rm He}}$ , ${^7_{\Lambda}{\rm Li}}$ , ${^7_{\Lambda}{\rm Be}}$ , ${^8_{\Lambda}{\rm Li}}$ , ${^8_{\Lambda}{\rm Be}}$ , ${^9_{\Lambda}{\rm Be}}$ , ${^{10}_{\Lambda}{\rm Be}}$ , ${^{10}_{\Lambda}{\rm B}}$ and ${^{13}_{\Lambda}{\rm C}}$ provide important information on the spin structure of the underlying Λ N interaction by comparing the calculated results with the recent experimental data by γ-ray hypernuclear spectroscopy. (2) The Λ-Σ coupling effect was investigated in ${^4_{\Lambda}{\rm H}}$ and ${^4_{\Lambda}{\rm He}}$ on the basis of the N?+?N?+?N?+?Λ (Σ) four-body model. (3) A systematic study of double-Λ hypernuclei and the Λ Λ interaction, based on the NAGARA event data ( ${^6_{\Lambda\Lambda}{\rm He}}$ ), was performed within the α +?x?+?Λ +?Λ cluster model (x = n, p, d, t,³He and α) and α +?α +?n?+?Λ +?Λ cluster model, (4) The Demachi-Yanagi event was interpreted as observation of the 2⁺ state of ${^{10}_{\Lambda \Lambda}{\rm Be}}$ , (5) The Hida event was interpreted as observation of the ground state of ${^{11}_{\Lambda \Lambda}{\rm Be}}$ .     

Hypernuclear spectroscopy program at JLab Hall C

Hypernuclear production by the (e,e^′K⁺) reaction has unique advantages in hypernuclear spectroscopy of the S=−1 regime. The second-generation spectroscopy experiment on ¹²C, ⁷Li and ²⁸Si targets has been recently carried out at JLab Hall C with a new experimental configuration (Tilt method) and also using a new high-resolution kaon spectrometer (HKS). The experiment is described and preliminary results are presented together with the empasis of significance of the (e,e^′K⁺) reaction for Λ hypernuclear spectroscopy and its future prospects.     

Hypernuclear production in the (K, π) reaction

Cross sections for the production of hypernuclei were measured in the reaction A(K⁻, π⁻) _ΛA. on light and heavy nuclear targets, using a separated K⁻ beam at the CERN Proton Synchrotron. The pions were detected in the forward direction. The results are compared with cross sections calculated under the assumption that the reaction took place on a single neutron. The good agreement between the measured and the calculated cross sections justifies the use of the (K⁻, π⁻) reaction in order to obtain spectroscopic information on hypernuclei.     

Field-induced spin-flip and spin-flip transitions in PrGa2

A detailed neutron diffraction study of a single crystal of hexagonal PrGa₂ under an applied field is presented. The field is applied along the easy [100] direction of the hexagonal plane. The compound exhibits several field-induced magnetic structures and, in particular, an uncompensated long period commensurate antiphase structure defined by the propagation vector (4/27, 4/27, 0) at zero field and below T_t = 3.5 K. Concerning the intermediate magnetic structures below T_t, two types of magnetic phase transitions are observed: a spin-flip transition where one moment per magnetic cell turns over, and a spin-slip transition from the low field commensurate propagation vector (4/27, 4/27, 0) to another commensurate vector (1/7, 1/7, 0). Between T_t and T_N = 7.2 K, the structure becomes apmlitude-modulated with a propagation vector (0.148, 0.148, 0.023). Important and original magnetic domain effects are also observed due to the high degeneracy of the easy direction of the hexagonal plane in both T<T_t and T_t<T<T_N regions.     

Recent Progress in Hypernuclear Physics

Hypernuclear physics has become very exciting owing to new epoch-making experimental data. The recent progress in theoretical and experimental studies of hypernuclei and discussion about the future development in this field are presented.     

Hypernuclear physics for neutron stars

The role of hypernuclear physics for the physics of neutron stars is delineated. Hypernuclear potentials in dense matter control the hyperon composition of dense neutron star matter. The three-body interactions of nucleons and hyperons determine the stiffness of the neutron star equation of state and thereby the maximum neutron star mass. Two-body hyperon–nucleon and hyperon–hyperon interactions give rise to hyperon pairing which exponentially suppresses cooling of neutron stars via the direct hyperon URCA processes. Nonmesonic weak reactions with hyperons in dense neutron star matter govern the gravitational wave emissions due to the r-mode instability of rotating neutron stars.     

Hypernuclear and strangeness physics program at J-PARC

The inauguration ceremony of the Japan Proton Accelerator Research Complex (J-PARC) was held on 6 July 2009, celebrating the completion of its construction. Now, the beam commissioning of the 50-GeV main proton synchrotron is in progress to improve the beam intensity and quality. Many important experimental programs are planned with the improved beams. In this report, some of them are introduced.     

Spectroscopy between 5 and 6 μm with a tunable spin-flip Raman source

We describe the application of a tunable, infrared, spin-flip Raman source to the measurement of the absorption spectra of gases in the spectral region 5–6 μm. Continuous tuning was obtained by using a low finesse Raman crystal cavity to eliminate mode pulling and hopping effects. The effects of atmospheric absorption, and pulse-to-pulse and magnetic field dependent intensity variations were cancelled by using a double beam arrangement. As an illustration of the operation of such a Raman spectrometer we obtain the P and Q branch absorption spectra of nitric oxide at various gas pressures in the spectral region 1890-1835 cm^-1. Studies at low gas pressure and with the tunable source operating close to the threshold for stimulated emission show a resolution of ≈ 0.08 cm^-1, determined by the linewidth of the Raman scattered radiation. This linewidth is shown to be in agreement with a mechanism of stimulated superradiant narrowing of the spontaneously scattered lineshape.