New isobar models for photo- and electroproduction of kaons on the proton were constructed utilizing new experimental data from LEPS, GRAAL, and particularly CLAS collaborations. Higher-spin nucleon (spin-3/2 and spin-5/2) and hyperon (spin-3/2) resonances were included using the consistent formalism and were found to play an important role in the description of data. The set of chosen nucleon resonances agrees well with the set of the most probable contributing states determined in the Bayesian analysis with the Regge-plus-resonace model. In our analysis, we paid special attention to model predictions of the cross section at small kaon angles since they are vital for accurate calculations of the hypernucleus-production cross section. What is more, in order to account for the unitarity corrections at the tree level, we have introduced energy-dependent decay widths of nucleon resonances. The energy-dependence of the decay width is then governed by the possibility of a given resonance to decay into various open channels and it also affects the choice of hadron form factors and the values of their cutoff parameters extracted in the fitting procedure.

On the road to electroproduction, we have implemented a new shape of electromagnetic form factors. For a reliable description of electroproduction at small virtual-photon mass Q², we found that it is necessary in our models to take into account a longitudinal coupling of virtual photons to nucleon resonances. The results of two versions of the isobar model will be compared with photo- and electroproduction data and the properties of the models will be discussed in great detail. In the case of electroproduction, we will present our new fit to data and discuss the significance of longitudinal couplings for good data description.

The appearance of hyperons in the core of a neutron star and the consequent softening of the equation of state have been questioned for a long time. The observation of massive neutron stars seems to rule out soft equations of state, apparently excluding the possibility of hyperon formation in the core of the star. The inconsistency between theoretical calculations and astrophysical observations, usually referred to as the hyperon puzzle, is based on our current knowledge of the interaction between strange particles and nucleons.

We give our contribution to the discussion by studying the general problem of the hyperon-nucleon interaction. We report quantum Monte Carlo calculations of single-Λ hypernuclei with A<50 based on phenomenological two- and three-body hyperon-nucleon forces. We present results for the Λ separation energy in different hyperon orbits, showing that the accuracy of numerical predictions exceeds that of currently available experimental data, especially for medium-mass hypernuclei. We show the results of a sensitivity study that indicates the possibility to investigate the nucleon-isospin dependence of the three-body hyperon-nucleon-nucleon force in the medium-mass region of the hypernuclear chart, where new spectroscopy studies are currently planned at the Thomas Jefferson National Accelerator Facility (JLab). The importance of such a dependence for the description of the physics of hypernuclei, and the consequences for the prediction of neutron star properties are discussed.

We have measured an excitation energy spectrum of the ¹²C(K^-,K⁺)X reaction at 1.8 GeV/c with an energy resolution of 5.4 MeV (FWHM), which is the best energy resolution ever achieved in studying this reaction. The measurement was performed at the K1.8 beam line of the J-PARC hadron experimental hall by using the SKS spectrometer, as a pilot run of J-PARC E05 experiment. The K^-beam intensity at the primary proton beam power of 39 kW was typically 6x10⁵/spill with 5.5-sec. beam cycle. The energy resolution was estimated from the peak observed  in the p(K^-,K⁺)Ξ^-reaction from a 9.54-g/cm²CH₂target. We took the data on the ¹²C(K^-,K⁺)X reaction with a 9.4-g/cm²C target for about 10 days. We have observed about 60k events of quasi-free Ξ^-production, and several tens of events in the bound region. While the analysis is near the final stage, we can see clear enhancements in the bound region above a flat background. Fitting to the enhancements with a few models suggest that the binding energy of  ¹²_ΞBe would be larger than the previously estimated value of about 4.5 MeV.