Nucleon spin with and without hyperon data: a new tool for analysis

We present a simple explanation of the underlying physics in the use of hyperon decay data to obtain information about proton spin structure. We also present an alternative input using nucleon magnetic moment data and show that the results from the two approaches are nearly identical. The role of symmetry breaking is clarified while pointing out that simple models explaining the violation of the Gottfried sum rule via pion emission tend to lose the good SU(3) predictions from Cabibbo theory for hyperon decays.     

Properties of hyperon stars rotating at Keplerian frequency

The structure and properties of a Keplerian rotating hyperon star with an equation of state (EOS) investigated using the relativistic σ--ω--ρ model are examined by employing an accurate numerical scheme. It is shown that there is a clear rotating effect on the structure and properties, and that hyperon star matter cannot support a star with a mass larger than 1.9 M_Θ, even a star rotating at the fastest allowed frequency. The constraints of the two known fastest rotating frequencies (716 Hz and 1122 Hz) on the mass and radius of a hyperon star are also explored. Furthermore, our results indicate that the imprint of the rapid rotation of a hyperon star on the moment of inertia is clear; the backward equatorial redshift, the forward equatorial redshift and the polar redshift can be distinguished clearly, the forward equatorial redshift is always negative; and its figuration is far from a spherical symmetric shape.     

Vertex constants (asymptotic normalization coefficients) and mean-square radii of hypernuclei in the potential model

The vertex constants, asymptotic normalization coefficients, and mean-square radii for a number of Λ hypernuclei have been calculated in a wide range of mass numbers. Interaction of a Λ hyperon with a core nucleus was described by the Woods-Saxon, Hultén, and Yukawa potentials. Geometric parameters of the Woods-Saxon potential were taken from the data in the literature, and the interaction force was fitted to the experimental binding energy of the ground state of this hypernucleus. The parameters of the Hulthén and Yukawa potentials were chosen so as to reproduce simultaneously the binding energy of the hyperon and its mean-square radius calculated with the Woods-Saxon potential. Within the effective-radius approximation, the low-energy parameters for hyperon scattering by the core nucleus are expressed in terms of vertex constants and the numerical values of these parameters are determined.     

Radiative corrections to semileptonic decays of charged hyperons

We have studied the radiative corrections to the lepton energy spectrum in semileptonic hyperon decays. The calculation is performed relativistically for the baryons as well as for the leptons, under the assumption of the effective current-current interaction of the V-?A type for the baryonic part. We obtain the explicit formula of radiative corrections to the lepton energy spectrum which we can exactly evaluate in case of charged hyperon decays. Numerical values of the radiative corrections to the decays rate and the shape of the lepton energy spectrum are also given for some decay modes. It is shown that the spectral shape is little affected by the radiative corrections.     

Absolute magnitude of non-leptonic hyperon decays and electromagnetic hyperfine splittings

In the quark model with current-current interaction, non-leptonic hyperon decays are controlled by the baryon wave function at small distances. An independent estimate of this quantify is provided by a related phenomenon: the baryon electromagnetic hyperfine splittings, given by the Fermi contact interaction. A good estimate is obtained with the standard Cabibbo-suppressed interaction. Important remaining problems for S-waves are emphasized.     

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 hypemuclear physics.In order to know the influences introduced by a single Lambda hyperon,we study the binding energy difference of mirror hypemuclear 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.     

A spectator-quark-model for the photoproduction of kaons

A simple model for the photoproduction of kaons off protons with a lambda hyperon in the final state is presented. In a quark model, the interaction is modelled by the pair-creation of the (anti-) strange quarks in the final state which recombine with the three quarks of the proton to form the lambda and kaon. The calculated scattering cross sections for photon energies up toE _ν = 1.9 GeV are compared to experiment. The pair-creation process is found to have a significant contribution to the total cross section.     

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.     

Experimental Activities in Few-Body Physics

Understanding the few-nucleon system remains one of the challenges in modern nuclear and hadron physics. Observables in few-nucleon scattering processes are sensitive probes to study the two and many-body interactions between nucleons in nuclei. In the past decades, several facilities provided a large data base to study in detail the three-nucleon interactions below the pion-production threshold by exploiting polarized proton and deuteron beams and large-acceptance detectors. Only since recently, the four-nucleon scattering process at intermediate energies has been explored. In addition, there is a focus to collect data in the hyperon-nucleon sector, thereby providing access to understand the more general baryon-baryon interaction. In this contribution, some recent results in the few-nucleon sector are discussed together with some of the preliminary results from a pioneering and exclusive study of the four-nucleon scattering process. Furthermore, this paper discusses the experimental activities in the hyperon sector, in particular, the perspectives of the hyperon program of PANDA.     

A Monte Carlo Study of Lambda Hyperon Polarization at BM@N

Heavy strange objects (hyperons) can provide essential signatures of the excited and compressed baryonic matter. At NICA, it is planned to study hyperons both in the collider mode (MPD detector) and the fixed-target one (BM@N setup). Measurements of strange hyperon polarization can give additional information on the strong interaction mechanisms. In heavy-ion collisions, such measurements are even more valuable since the polarization is expected to be sensitive to characteristics of the QCD medium (vorticity, hydrodynamic helicity) and to QCD anomalous transport. In this analysis, the possibility to measure at BM@N the polarization of the lightest strange hyperon Λ is studied in Monte Carlo event samples of Au + Au collisions produced with the DCM-QGSM generator. It is shown that the detector will allow to measure polarization with a precision required to check the model predictions.     

重离子碰撞中阈能附近超子产生机制

在量子分子动力学输运模型LQMD(Lanzhou quantum molecular dynamics transport model)框架下,研究了不同重离子反应系统中同位旋和核介质效应对超子产生以及动能谱的影响.基于手征有效场理论,引入了动量和密度相关的排斥超子-核子光学势,并且考虑了该势对超子产生截面阈能的修正....     

SINGLE K MESON AND 2π, πρ EXCHANGES IN THE Λ-N INTERACTION

The purpose of this paper is to study, the A-N interaction by using meson exchange theory. We have considered three processes: ⅰ) Single K meson exchange, ⅱ) Box diagrams of 2π and πρ exchanges with a nucleon in the intermediate states, and ⅲ) Box diagrams of 2π and πρ exchange with an isobar in the intermediate states. For simplicity, two approximations are used in the calculation. First, the initial nucleon N and hyperon are considered to be at rest. Second, an average value is used for the energies of the intermediate states. The results are qualitatively consistent with experiments.     

A nuclear optical potential on the Λ hyperon

A nuclear optical potential acting on the Λ hyperon is evaluated within the framework of the G-matrix theory and the local density approximation by employing the Nijmegen OBE model D interaction.     

Investigation of Hypernucleus Λ5He Structure and the Calculation of the Binding Energy

In this paper the nuclear structure of hypernucleus ₅^ΛHe and its effect on the binding energy B_Λ of A hyperon are systematically studied. The Polarization effect of the core a is explored. The binding energy B_Λ of ₅^ΛHe including D-state mixing component is calculated. The results show that the core α suffers a serious distortion by the interaction with Λ hyperon and has no longer the structure of a free Alpha Particle. The D-state mixing can improve the B_Λ calculated value about 0.5MeV. A Possible three cluster structure is further explored. The Λ+d+d model can give a B_Λ value close to the experimental one. The further exploration is necessary.     

Massive neutron stars and their implications

Recent observations of high mass pulsar PSRJ1614-2230 has raised serious debate over the possible role of exotics in the dense core of neutron stars. The precise measurement of mass of the pulsar may play a very important role in limiting equation of state (EoS) of dense matter and its composition. Indirectly, it may also shape our understanding of the nucleon–hyperon or hyperon–hyperon interactions which is not well known. Within the framework of an effective chiral model, we compute models of neutron stars and analyse the hyperon composition in them. Further related implications are also discussed.     

Gravitational waves from the axial perturbations of hyperon stars

The eigen-frequencies of the axial w-mode oscillations of hyperon stars are examined.It is shown that as the appearance of hyperons softens the equation of state of the super-density matter,the frequency of gravitational waves from the axial w-mode of hyperon star becomes smaller than that of a traditional neutron star at the same stellar mass.Moreover,the eigenfrequencies of hyperon stars also have scaling universality.It is shown that the EURO thirdgeneration gravitational-wave detector has the potential to detect the gravitational-wave signal emitted from the axial w-mode oscillations of a hyperon star.     

能通过大质量中子星转动惯量来限定超子参数吗?

在相对论平均场理论（RMFT）框架内,使用GL91参数组结合超核数据和大质量中子星的观测数据限定超子标量耦合参数X_σ=0.59~1.0,用慢转近似计算了大质量中子星和前中子星的转动惯量。当X_σ从0.59增加到1.0,中子星（前中子星）的最大转动惯量增幅达89%（60%）。在同样的变化范围内,用Crab的观测数据,计算得到中子星（前中子星）的最大能量损失（dE/dt）的增幅为44%（25%）,最大磁场增幅为48%（38%）。相比于前中子星,中子星的性质对超子参数更为敏感。当X_σ从0.59增加到1.0,PSR J0348+0432的转动惯量和dE/dt的增幅均为14%,而磁场减幅为10%。如果天文观测能够给出中子星转动惯量的上限,或者同时精确测量中子星的质量和转动惯量,能帮助人们进一步限定超子参数。In the framework of the relativistic mean field theory(RMFT) with GL91 cets, the momentum of inertia (I) of slowly rotating neutron stars is studied by perturbative approach. The scalar hyperon coupling should lie in the range of X_σ=0.59~1.0 to be compatible with massive neutron stars. As X_σ increases from 0.59 to 1.0, the maximum momentum of inertia(I_max) of neutron (protoneutron) stars increases by 89% (60%). According to the data of Crab, the maximum energy loss(dE/dt) of neutron (protoneutron) stars will increase by 44%(25%)and the maximum magnetic field (B) will increase by 48%(38%). I and dE/dt of PSR J0348+0432 both increase by 14%, while B decreases by 10% as X_σ increases from 0.59 to 1.0. So if the upper bound of I, or the accurate values of both the mass and I of neutron stars could be provided by the astronomical observations, the hyperon couplings should be further constrained in the future.     

Monomolecular film and absorption behavior of polymers having carboxyl groups

π-A isotherms of monolayers of various copolymers containing carboxyl groups derived from acrylic acid (AA) were measured. The conformation of polymer adsorbed on the water surface and interaction forces between polymer and water surface (considered to be a model for the surface of inorganic powders) owing to AA groups is discussed based on the π-A isotherms.

Polyacrylic esters having a small amount of AA groups formed the expanded type of monolayer. AA groups cause an increase in the interaction force between the polymer and water surface. Polymethyl methacrylate having a small amount of AA groups formed condensed-type monolayers, while with a large amount of AA groups it showed two types of monolayer collapse. Though polystyrene could not spread as a mono-layer, poly (styrene-acrylic acid) [p(St-AA)] copolymer formed a monolayer when the AA content was over 4 mol %. The adsorbance of P(St-AA) on water, calculated from π-A isotherm, is the same as that obtained on α-Fe₂O₃ independently. This means the conformation of the polymer on the solid surface and the interaction force can be discussed by using the π-A isotherm.     

Hyperon coupling dependence of hadron matter properties in relativistic mean field model

The properties of hadronic matter at β equilibrium in a wide range of densities are described by appropriate equations of state in the framework of the relativistic mean field model. Strange meson fields, namely the scalar meson field σ＊（975） and the vector meson field φ（1020）, are included in the present work. We discuss and compare the results of the equation of state, nucleon effective mass, and strangeness fraction obtained by adopting the TM1, TMA, and GL parameter sets for nuclear sector and three different choices for the hypcron couplings. We find that the parameter set TM1 favours the onset of hyperons most, while at high densities the GL parameter set leads to the most hyperon-rich matter. For a certain parameter set （e.g. TM1）, the most hyperon-rich matter is obtained for the hyperon potential model. The influence of the hyperon couplings on the effective mass of nucleon, is much weaker than that on the nucleon parameter set. The nonstrange mesons dominate essentially the global properties of dense hyperon matter. The hyperon potential model predicts the lowest value of the neutron star maximum mass of about 1.45 Msun to be 0.4--0.5 Msun lower than the prediction by using the other choices for hyperon couplings.[第一段]