Hypernuclear Spectroscopy with Stable Heavy Ion Beams and Rare-isotope Beams:HypHI Project at GSI and FAIR

The international HypHI collaboration proposes to perform hypernuclear spectroscopy with stable heavy ion beams and rare isotope beams at GSI and FAIR in order to study neutron and proton rich hypernuclei and to measure directly hypernuclear magnetic moments for the first time.The project is divided into four phases.In the first Phase 0 experiment,the feasibility of precise hypernuclear spectroscopy with heavy ion beams will be demonstrated by observing π~- decay channels of ~e_ΛH,~4_ΛH and ~5_ΛHe with ~6Li projectiles at 2 AGeV impinging on a ~(12)C target.In the later Phases 1 through 3,studies of proton and neutron rich hypernuclei,direct measurements of hypernuclear magnetic moments and the spectroscopy of hypernuclei toward the nucleon drip-lines are planned.     

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..     

The Third Generation (e,e′K~+) A Hypernuclear Spectroscopy at Jlab

We are now preparing for the third generation (e,e′K~+) A hypernuclear spectroscopic experiment at Hall C,Jefferson Lab (USA).The goal of the experiment is the precise spectroscopy of hypernuclei in wide mass region.We have constructed a new high resolution electron spectrometer "HES" dedicated to (e,e′K~+) hypernuclear study in Japan and it was shipped to JLab in February,2008.We will discuss about the physics of the (e,e′K~+) hypernuclear study at JLab and report the current preparation status of the third generatrion experiment.     

FINUDA,a hypernuclear physics experiment

FINUDA is a hypernuclear physics experiment to be held from the summer of 2002. The hypernuclear physics program and the apparatus characteristics and performances are here reviewed.     

Optical potential study of Σ nuclear states

Single-particle energies and widths of Σ hypernuclear states are calculated in light systems (A ≤ 40) as energy eigenvalues of the Schrödinger equation for a complex optical potential that fits level shifts and widths of Σ^? atoms. The interpretation and significance of Σ (normalizable) bound states embedded in the Λ hypernuclear (as well as, sometimes, in the Σ hypernuclear) continuum are discussed and their properties are studied, primarily in order to identify relatively narrow (Γ ? 10 MeV) states. The connection between these calculations and the recently observed Σ hypernuclear states suggests that bound states embedded in the Σ continuum, rather than (nonnormalizable) Gamow resonant states, are produced in (K^?, π) nuclear reactions.     

Angular distributions for (3,4)(Lambda)H bound states in the (3,4)He(e,e(')K+) reaction

The (3,4)(Lambda)H and (4)(Lambda)H hypernuclear bound states have been observed for the first time in kaon electroproduction on (3,4)He targets. The production cross sections have been determined at Q(2)=0.35 GeV2 and W=1.91 GeV. For either hypernucleus the nuclear form factor is determined by comparing the angular distribution of the (3,4)He(e,e(')K+)(3,4)(Lambda)H processes to the elementary cross section 1H(e,e K+)Lambda on the free proton, measured during the same experiment.     

QED effects in Cu-like Pb recombination resonances near threshold

In an electron-ion recombination study with Pb53+ dielectronic recombination resonances are found for as low as approximately 10(-3)-10(-4) eV relative energy. The resonances have been calculated by relativistic many-body perturbation theory and through comparison with experiment the Pb53+(4p(1/2)-4s(1/2)) energy splitting of approximately 118 eV is determined with an accuracy comparable to the position of the first few resonances, i.e., approximately 10(-3) eV. Such a precision provides a test of QED in a many-body environment at a level which can still not be reached in calculations.     

The production of narrow Σ-hypernuclear states

It has been suggested that some of the observed narrow Σ hypernuclear states may be “bound states in the continuum” of the Σ interacting with the host nucleus formed when that interaction is strongly absorptive. It is shown that the S matrix for such a process vanishes at the complex energy of such a bound state. Some general properties of the S matrix in the presence of absorption are derived.     

γ-ray Spectroscopy of Hypernuclei.Recent KEK Results and Future Plans at J-PARC

In this proceeding,we will first outline the experimental setup and main results of the most recent hypernuclear γ-ray spectroscopy experiment (KEK-E566) performed at KEK-PS K6 beam line.The main feature and characteristics of this type of research will he emphasised.After that,the approved experimental proposal (E13) at J-PARC facility will be introduced briefly.     

Interaction mean free path in the emulsion and interaction radius of the nucleus

The interaction mean free path of the high energy nucleus in the emulsion is studied with the Glauber model and Hartree-Fock type variational calculation for the nuclear structure. It is found that the experimentally observed interaction mean free paths are well reproducible. It is also found that the interaction radius of the projectile nucleus can be determined with the emulsion experiment.     

Impurity nuclear physics

Using a germanium-detector array for hypernuclear γ spectroscopy (Hyperball), we measured B(E2) of the ⁷ _ΛLi hypernucleus and observed a significant shrinkage of the ⁶Li core induced by a Λ-particle. In this way, nuclear properties can be drastically changed by introducing a Λ-particle, which can be investigated by high-resolution hypernuclear γ spectroscopy. In the future neutron-rich hypernuclei will also be studied, where interesting modifications of nuclear structure by a Λ-particle are expected. Received: 1 May 2001 / Accepted: 4 December 2001     

AMANDA observations constrain the ultrahigh energy neutrino flux

A number of experimental techniques are currently being deployed in an effort to make the first detection of ultrahigh energy cosmic neutrinos. To accomplish this goal, techniques using radio and acoustic detectors are being developed, which are optimally designed for studying neutrinos with energies in the PeV-EeV range and above. Data from the AMANDA experiment, in contrast, have been used to place limits on the cosmic neutrino flux at less extreme energies (up to approximately 10 PeV). In this Letter, we show that by adopting a different analysis strategy, optimized for much higher energy neutrinos, the same AMANDA data can be used to place a limit competitive with radio techniques at EeV energies. We also discuss the sensitivity of the IceCube experiment, in various stages of deployment, to ultrahigh energy neutrinos.     

Hypernuclear physics studies of the PANDA experiment at FAIR

Hypernuclear research will be one of the main topics addressed by the PANDA experiment at the planned Facility for Antiproton and Ion Research FAIR at Darmstadt (Germany). http://www. gsi.de, http://www.gsi.de/fair/ Thanks to the use of stored \(\overline {p}\) beams, copious production of double Λ hypernuclei is expected at the PANDA experiment, which will enable high precision γ spectroscopy of such nuclei for the first time, and consequently a unique chance to explore the hyperon-hyperon interaction. In particular, ambiguities of past experiments in determining the strength of the ΛΛ interaction will be avoided thanks to the excellent energy precision of a few keV (FWHM) achieved by germanium detectors. Such a resolution capability is particularly needed to resolve the small energy spacing of the order of (10–100) keV, which is characteristic from the spin doublet in hypernuclei the so -called ”hypernuclear fine structure”. In comparison to previous experiments, PANDA will benefit from a novel technique to assign the various observable γ-transitions in a unique way to specific double hypernuclei by exploring various light targets. Nevertheless, the ability to carry out unique assignments requires a devoted hypernuclear detector setup. This consists of a primary nuclear target for the production of \({\Xi }^{-}+\overline {\Xi }\) pairs, a secondary active target for the hypernuclei formation and the identification of associated decay products and a germanium array detector to perform γ spectroscopy. Moreover, one of the most challenging issues of this project is the fact that all detector systems need to operate in the presence of a high magnetic field and a large hadronic background. Accordingly, the need of an innovative detector concept will require dramatic improvements to fulfil these conditions and that will likely lead to a new generation of detectors. In the present talk details concerning the current status of the activities related to the detector developments for this challenging programme will be given. Among these improvements is the new concept for a cooling system for the germanium detector based on a electro-mechanical device. In the present work, the cooling efficiency of such devices has been successfully tested, showing their capability to reach liquid nitrogen temperatures and therefore the possibility to use them as a good alternative to the standard liquid nitrogen dewars. Furthermore, since the momentum resolution of low momentum particles is crucial for the unique identification of hypernuclei, an analysis procedure for improving the momentum resolution in few layer silicon based trackers is presented.     

γ -ray spectroscopy study of 11 ΛB and 12 ΛC

In this paper, a preliminary result from the latest hypernuclear γ -ray spectroscopy experiment (KEK-E566) is presented together with a short discussion. The experiment was performed at the KEK-PS K6 beam line in 2005. In this experiment, the ¹²C(π⁺, K ⁺)¹² _ΛC reaction was employed to populate ¹² _ΛC/¹¹ _ΛB hypernuclei. A germanium detector array, Hyperball2, was constructed to detect γ -rays emitted from the hypernuclei produced. Three hypernuclear γ -ray peaks were observed and assigned.     

Atomistic properties of γ uranium

The properties of the body-centered cubic γ phase of uranium (U) are calculated using atomistic simulations. First, a modified embedded-atom method interatomic potential is developed for the high temperature body-centered cubic (γ) phase of U. This phase is stable only at high temperatures and is thus relatively inaccessible to first principles calculations and room temperature experiments. Using this potential, equilibrium volume and elastic constants are calculated at 0 K and found to be in close agreement with previous first principles calculations. Further, the melting point, heat capacity, enthalpy of fusion, thermal expansion and volume change upon melting are calculated and found to be in reasonable agreement with experiment. The low temperature mechanical instability of γ U is correctly predicted and investigated as a function of pressure. The mechanical instability is suppressed at pressures greater than 17.2 GPa. The vacancy formation energy is analyzed as a function of pressure and shows a linear trend, allowing for the calculation of the extrapolated zero pressure vacancy formation energy. Finally, the self-defect formation energy is analyzed as a function of temperature. This is the first atomistic calculation of γ U properties above 0 K with interatomic potentials.     

Scattering of atomic beams by surface and bulk phonons

The general expressions obtained in a previous work are further developed to get general formulae for one-phonon scattering of atomic beams in closed form. The scattering by bulk and surface phonons are discussed separately and the respective scattered energy spectra and behaviour near the Bragg angles are carefully treated. Interesting differences are found, which may have experimental importance in separating events of scattering from different modes. The expressions for the inelastic scattering differential cross-sections obtained are applied to the experiment by Williams et al. on the He/NaF(001) system. Despite the use of estimated values for the unknown parameters, a good quantitative agreement with the experiment is obtained, and the structure observed by Williams near the specular peak is clearly explained. The contribution of transverse bulk modes is found to be about 30% of that of transverse surface modes. The contribution of longitudinal modes in smaller than the contribution of the respective transverse modes by a factor 0.01.     

High-resolution gamma-ray spectroscopy of ΛLi

We report on the first observation of hypernuclear γ transitions using germanium detectors. Using a large-acceptance Ge detector system, we observed two γ transitions in _Λ⁷Li, the spin-flip transition at 689±4keV and the transition at 2050±2 keV (preliminary). The strength of the ΛN spin-spin interaction is derived from the energy of the former transition. As for the latter transition, B(E2) was measured to be 3.9±0.6±0.4 e²fm⁴ (preliminary), which indicates a shrinkage of the nuclear size of _Λ⁷Li from ⁶Li and confirms “glue-like role” of Λ.     

The Role of One Single Lambda Hyperon on Binding Energy Difference of Hypernuclear Mirror Pair

Investigation on isospin symmetry in light Lambda hypernuclei is one of the most important issues in hypernuclear physics. In order to know the influences introduced by a single Lambda hyperon, we study the binding energy difference of mirror hypernuclear pair with mass A=16, 18, 28, 40, and 42 using a time-odd triaxial relativistic mean field theory. Effects as the spin-orbit interaction, the time-odd component of vector fields, the core polarization, the proton-neutron mass difference, and the center-of-mass energy correction are self-consistently considered. Compared to the reported results of ordinary nuclei, the binding energy difference of mirror hypernuclei shows trivial change. With core polarization modified by an impurity hyperon, the isospin nonconserving effect between proton and neutron is hardly reduced for nuclei in study.     

Constraints on the symmetry energy using the mass-radius relation of neutron stars

The nuclear symmetry energy is intimately connected with nuclear astrophysics. This contribution focuses on the estimation of the symmetry energy from experiment and how it is related to the structure of neutron stars. The most important connection is between the radii of neutron stars and the pressure of neutron star matter in the vicinity of the nuclear saturation density n_s. This pressure is essentially controlled by the nuclear symmetry energy parameters S_v and L , the first two coefficients of a Taylor expansion of the symmetry energy around n_s. We discuss constraints on these parameters that can be found from nuclear experiments. We demonstrate that these constraints are largely model-independent by deriving them qualitatively from a simple nuclear model. We also summarize how recent theoretical studies of pure neutron matter can reinforce these constraints. To date, several different astrophysical measurements of neutron star radii have been attempted. Attention is focused on photospheric radius expansion bursts and on thermal emissions from quiescent low-mass X-ray binaries. While none of these observations can, at the present time, determine individual neutron star radii to better than 20% accuracy, the body of observations can be used with Bayesian techniques to effectively constrain them to higher precision. These techniques invert the structure equations and obtain estimates of the pressure-density relation of neutron star matter, not only near n_s, but up to the highest densities found in neutron star interiors. The estimates we derive for neutron star radii are in concordance with predictions from nuclear experiment and theory.