Narrow Results

The roles of the COSY-TOF and COSY-ANKE spectrometers in the measurement of strange meson production are briefly reviewed, mainly in connection with new results on the pp → K⁺pΛ, pp → K⁺pΣ⁰ and pp → K⁺nΣ⁺ reactions.

Within an extended chiral constituent quark model, three- and five-quark structure of the S₀₁ resonance Λ(1405) is investigated with respect to the coupling constants and . Our findings corroborate with about 50% of five-quark admixture in the Λ(1405) needed in reproducing the strong decay width, Γ_{Λ(1405)→(Σπ)°}.

This is a short survey of signatures and characteristics of the quark–gluon plasma in the light of experimental results that have been obtained over the past three decades. In particular, we present an in-depth discussion of the strangeness observable, including a chronology of the experimental effort to detect QGP at CERN-SPS, BNL-RHIC, and CERN-LHC.

Protoneutron stars are hot and lepton rich objects formed in type II supernovae. It is natural to regard the evolution of these stars as taking place in several stages. This paper describes results of analysis of protoneutron star evolution for models incorporating an strangeness-rich, neutrino opaque matter equation of state. Of special interest in this paper is the comparison of protoneutron star models for two different phases. One characterized by neutrino trapping and by the value of entropy s=1 and the other, formed when neutrinos leak out of the system, described as a hot deleptonized star. The equation of state adequate for the protoneutron star has been constructed. It has been shown that the maximum stable protoneutron star mass is close to 1.44 M_⊙.

The possible existence of $\mathrm{\Delta }$ resonances is inspected in the cold dense matter of neutron star (NS) core in the presence of hyperons. The diverse effects of variation in $\mathrm{\Delta }$ mass on their formation and the equation of state (EoS) are studied in this work with an effective chiral model and the resultant NS properties are calculated with the help of parameterized Tolman–Oppenheimer–Volkoff (PTOV) equations to bring out the two important features of pressure in the context of massive NSs. The $\mathrm{\Delta }$ puzzle is re-explored and resolved taking into account the concept of modified/parametrized inertial pressure and self-gravity in case of massive pulsars like PSR J1614−2230 and PSR J0348-0432. It is seen that although the presence of exotic matter like the hyperons and $\mathrm{\Delta }s$ softens the EoS considerably, their presence in massive NSs can be successfully explained with the theory of parametrized hydrostatic equilibrium conditions. The results of this work also satisfy the constraints on $R_{1.4}$ and $R_{1.6}$ from the gravitational wave (GW170817) detection of binary NS merger. The constraint on baryonic mass from PSR J0737-3039 is also satisfied with the solutions of the PTOV equations for all the $\mathrm{\Delta }$ masses considered.

A brief overview of strangeness physics with the CLAS detector at JLab is given, mainly covering the domain of nucleon resonances. Several excited states predicted by the symmetric constituent quark model may have significant couplings to the KΛ or KΣ channels. We will discuss data that are relevant in the search for such states in the strangeness channel, and give an outlook on the future prospects of the N* program at JLab with electromagnetic probes.

Jefferson Lab experiment E91-016 studied kaon electroproduction on hydrogen, deuterium and helium targets at a beam energy of 3.245 GeV and four-momentum transfer, Q², ranging from 0.34 to 0.5 GeV². Among a variety of other topics, part of this study was the investigation of the threshold region for signatures of final-state interaction between the electroproduced Λ-hyperon and spectator neutron. Compared to a purely quasi-free description, an excess yield was observed in the threshold region. This is compared to the predictions from three different hyperon-nucleon potentials. Though the data exhibit some sensitivity to the tested hyperon-nucleon potentials, further studies would require a more dedicated measurement with better resolution in the threshold region.

Adopting the equation of states (EOSs) from the relativistic mean field (RMF) theory, the relationships among the keplerian frequency f_K, gravitational mass M and radius R for the rapidly rotating neutron stars with and without hyperons are presented and analyzed. For various RMF EOSs, the empirical formula , proposed by P. Haensel et al. [Astron. Astrophys.502 (2009) 605], is found to be an approximation with the error at most 13% and such approximation is worse for the neutron stars with hyperons. It indicates that the errors should be considered when the empirical formula is used to discuss the properties of neutron stars.

We study the effects of anisotropic pressure (AI-P) on properties of the neutron stars (NSs) with hyperons inside its core within the framework of extended relativistic mean field. It is found that the main effects of AI-P on NS matter is to increase the stiffness of the equation of state EOS, which compensates for the softening of the EOS due to the hyperons. The maximum mass and redshift predictions of anisotropic neutron star with hyperonic core are quite compatible with the result of recent observational constraints if we use the parameter of AI-P model h ≤ 0.8 [L. Herrera and W. Barreto, Phys. Rev. D88 (2013) 084022.] and Λ ≤ -1.15 [D. D. Doneva and S. S. Yazadjiev, Phys. Rev. D85 (2012) 124023.]. The radius of the corresponding NS at M = 1.4 M_⊙ is more than 13 km, while the effect of AI-P on the minimum mass of NS is insignificant. Furthermore, due to the AI-P in the NS, the maximum mass limit of higher than 2.1 M_⊙ cannot rule out the presence of hyperons in the NS core.

We consider the so-called hyperon puzzle of neutron star (NS). We employ Skyrme force models for the description of in-medium nucleon–nucleon (NN), nucleon–Lambda hyperon ($N\mathrm{\Lambda }$) and Lambda–Lambda ($\mathrm{\Lambda }\mathrm{\Lambda }$) interactions. A phenomenological finite-range force (FRF) for the $\mathrm{\Lambda }\mathrm{\Lambda }$ interaction is considered as well. Equation of state (EoS) of NS matter is obtained in the framework of density functional theory, and Tolman–Oppenheimer–Volkoff (TOV) equations are solved to obtain the mass-radius relations of NSs. It has been generally known that the existence of hyperons in the NS matter is not well supported by the recent discovery of large-mass NSs ($M\simeq 2M_{\odot }$) since hyperons make the EoS softer than the one without them. For the selected interaction models, $N\mathrm{\Lambda }$ interactions reduce the maximum mass of NS by about 30%, while $\mathrm{\Lambda }\mathrm{\Lambda }$ interactions can give about 10% enhancement. Consequently, we find that some Skyrme force models predict the maximum mass of NS consistent with the observation of $2M_{\odot }$ NSs, and at the same time satisfy observationally constrained mass-radius relations.

Models of neutron stars (NSs) with hyperon cores are constructed with an effective chiral model in mean-field approximation. The hyperon couplings are fixed by reproducing their experimentally determined binding energies. The impact of these couplings on population of different particles and the equation of state (EoS) are studied in this work. The global properties of NSs like gravitational mass, radius, baryonic mass and central density are calculated using parametrized Tolman–Oppenheimer–Volkoff equations (PTOVs) with special emphasis on two effects of pressure — one contributing to total mass density and the other to self-gravity of the star. We find that with PTOV solutions in static conditions, a softer EoS (including hyperons) can also lead to massive stellar configurations of NSs, which are in good agreement with the observed maximum mass bound of $\approx 2M_{\odot }$ (PSR J0348-0432). Estimates of $R_{1.4}$ and $R_{1.6}$, obtained with the PTOV equations, are consistent with the recent findings of the same from the data analysis of gravitational waves (GW170817) observation.

In this paper, we review the calculation of suppression of Chiral Separational and Chiral Vortical Effects for strange quarks (which allegedly yield spin polarization of $\mathrm{\Lambda }∕\bar{\mathrm{\Lambda }}$-hyperons in peripheral Heavy-Ion Collisions) by the nonperturbative interactions in hot deconfined QCD with the Field Correlator Method. The parameter range in the temperature-baryon density plane is expected to cover LHC-ALICE and RHIC-STAR data.

Utilizing the GKLS master equation we show that the decay property of a particle can be straightforwardly incorporated. In standard particle physics the decay is often described by an efficient non-hermitian Hamiltonian, in accord with the seminal Wigner-Weisskopf approximation. We show that by enlarging the Hilbert space and defining specific GKLS operators we have attained a formalism with a hermitian Hamiltonian and probability conserving states. This proves that the Wigner-Weisskopf approximation is Markovian and completely positive. In addition, this formalism allows a straightforward generalization to many-particle decays. Last, but not least, some impacts of the GKLS master equation onto systems at high energies are reported, such as for neutral meson, neutrino and hyperon systems.

Measurement results of photoproduced excited hyperon states using the CLAS detector at Jefferson Lab are shown. The invariant mass distribution of the Λ(1405) has recently been shown to be different for each of the three Σπ channels that it decays to, showing that there is prominent interference between the isospin I = 0 and I = 1 isospin amplitudes. Measurements of the differential and total cross sections of the three hyperons Λ(1405), Σ⁰(1385), and Λ(1520) are presented and compared. Prospects of future studies using a 12 GeV beam with the GlueX detector are briefly given.

We investigate quark to $\mathrm{\Lambda }$ and $\bar{\mathrm{\Lambda }}$ longitudinal spin transfers in the light-cone SU(6) quark sepctator-diquark model and try to analyze the possible origins for the spin transfer difference between them measured by the COMPASS collaboration. The intermediate heavier hyperon decay processes are considered, while the final hadron transverse momentum is also included. We find that after taking into account the asymmetric nucleon $s/\bar{s}$ distribution effect, the results we get are qualitatively comparable with the difference of the COMPASS experimental data.

The year 2019 marks the 30^th anniversary of BES and the 100^th anniversary of Rutherford’s discovery of the proton. In spite of the fact that when BES operations started the proton was already 70 years old and the strange hyperons were all over 25, BES continues to make important and unique measurements of nucleon and hyperon properties, including some interesting discoveries.

Although Belle stopped data taking more than ten years ago and Belle II has already started data taking, Belle is still producing many excited results on hyperons. Recently Belle confirmed the existence of Ξ(1620)⁰ via ${\mathrm{\Xi }}_c^{+}\to {\mathrm{\Xi }}^{-}{\pi }^{+}{\pi }^{+}$ decays and observed a new excited Ω state decaying into Ξ⁰K⁻ and ${\mathrm{\Xi }}^{-}{K}_S^0$ in ϒ(1S, 2S, 3S) decays.

We present two recent parametrizations of the equation of state (FSU2R and FSU2H models) that reproduce the properties of nuclear matter and finite nuclei, fulfill constraints on high-density matter stemming from heavy-ion collisions, produce 2M_⊙ neutron stars, and generate neutron star radii below 13 km. Making use of these equations of state, cooling simulations for isolated neutron stars are performed. We find that two of the models studied, FSU2R (with nucleons) and, in particular, FSU2H (with nucleons and hyperons), show very good agreement with cooling observations, even without including nucleon pairing. This indicates that cooling observations are compatible with an equation of state that produces a soft nuclear symmetry energy and, thus, generates small neutron star radii. Nevertheless, both schemes produce cold isolated neutron stars with masses above 1.8M_⊙.

The NA48 Collaboration has obtained several new results on kaon and neutral hyperon decays. For hyperons we present new, very precise measurements on the Ξ⁰ lifetime and the decay asymmetries of Ξ⁰ → Λγ and Ξ⁰ → Σ⁰γ. On kaon decays, we report on the first observation of the interference term between Inner Bremsstrahlung and Direct Emission in K^± → π^±π⁰γ and on a new, accurate measurement of the form factor slopes in the semileptonic decay K_L → π^±μ^∓ν.

The structure and decay modes of the K^--condensed hypernucleus, which may be produced in the laboratory as the strangeness-conserving system, is investigated on the basis of the effective chiral Lagrangian for the kaon-baryon interaction, combined with the nonrelativistic baryon-baryon interaction model. It is shown that a large number of negative strangeness is needed for the formation of highly dense and self-bound state with K^- condensates and that part of the strangeness should be carried by hyperons. Such a self-bound object may decay only through weak processes.