The activity of the Department covers the following problems in nuclear physics:
Investigation of nuclear resonances in electromagnetic decays using dielectron radiation and HADES@GSI spectrometer
The study of the excited states of the nucleon (so-called resonances) is an excellent tool for understanding the nature of the strong interactions, responsible for the existence of hadrons and the generation of the mass of visible matter in the Universe. The main goal of the research is understanding the resonance mass spectrum, in particular solving the problem of the so-called missing resonances, predicted by the quark model and not confirmed experimentally, and their internal structure. Based on previous observations, we know that the nucleon and its resonances are not simple states, composed of three static quarks, and that the dynamics of the gluon interaction plays a very large role, which is responsible for generating the mass of light quarks \((u, d, s)\) and spontaneous chiral symmetry breaking. As a result of the chiral symmetry breaking the appearance of quark condensates is expected, which can be interpreted as a cloud surrounding the quarks and generating their effective mass. An important role in the description of the properties of nucleons (and resonances) is also played by the meson cloud surrounding the quark core.
Production and decays of baryon resonances in pion-induced reactions
The HADES experimental program focuses on two main goals. The first one is to measure the emission of dielectrons (electron-positron pairs) from compressed baryon matter formed in collisions of heavy ions, and to study the properties of hadron in the medium. The second goal is to study the production of dielectrons in elementary proton – proton \((pp)\) and pion – proton \((\pi p)\) collisions, and understanding the electromagnetic structure of baryons. Both goals are complementary in the sense that understanding effects in media also includes studies of dielectron invariant mass spectra in elementary reactions \(\pi p\), \(pp\). Elementary collisions, especially those with pion beams, also provide an excellent opportunity to study baryon resonances, i.e. short-term excited states of nucleons and their coupling with mesons of light vectors \((\rho/\omega)\), which play an essential role in inmedium modifications.
Study of the production and decay of electromagnetic hyperons at SIS18/FAIR energies using a new tracking detector in the HADES detection system
Searching for the effects of the time reversal symmetry breaking
As a laboratory in these studies, we use the decay of free neutrons. The search for the source of symmetry breaking may appear in the non-zero value of the electric dipole moment of the neutron, as well as in the exotic, as extremely difficult to measure, correlation coefficients in this decay (such as the \(R\) factor between the spin of the neutron, the momentum of the electron coming from its decay, and the transverse polarization this electron). Experiments are being conducted at the Paul Scherrer Institute, Villigen, Switzerland.
Investigation of the properties of nuclear matter in collisions of heavy ions at intermediate energies
The leading topic in this field is the study of the dependence of the nuclear symmetry energy onnuclear matter density. This relationship is important not only in nuclear physics but also in astrophysics. Experimental research was conducted at GSI (ASY-EOS experiment) and continued at RIKEN (S\(\pi\)RIT cooperation). Experimental research is related to the development of innovative detection techniques (KRATTA and KATANA detectors), as well as the development of data analysis methods and model simulations of the tested reactions and detection systems.
Study of hadronic interactions in nuclear matter
The nuclear spallation reactions are good laboratory for studying hadronic interactions in nuclear matter. When the particle bombarding the atomic nucleus is a hadron (e.g. a proton), it interacts with the nucleons of the medium, transferring its energy and momentum to the nucleus system. It also causes the formation of an intranuclear cascade of interactions of the nucleons gaining energy in the collision reaction. The mechanism of this interaction, the rate of the energy dissipation in the bombarded nucleus, and the number of nucleons involved in the cascade, significantly affect the types, energies and momenta of the particles emitted from the excited nucleus. Unraveling the mechanism of the hadronic interaction in nuclear matter consists in precise measurements of the distribution of the particles emitted in spallation reactions and the creation of theoretical models of interaction and mutual comparison of results. The data from the PISA (Proton Induced SpAllation) experiment and numerous data available in the scientific literature are used. The course of interactions is simulated using models of individual reaction phases, both self-developed – SMC++ (Spallation Model with Cascade++) and other available models such as INCL, GEM, ABLA, SMM, GEMINI. A particularly interesting issue related to the interaction of hadrons in nuclear matter is the so far unknown mechanism of the formation of multinucleon particles (deuterons, tritons, 3He, 4He, ….) with high energies, numerous in experimental data. both own – SMC++ (Spallation Model with Cascade++) and other available models such as INCL, GEM, ABLA, SMM, GEMINI. A particularly interesting issue related to the interaction of hadrons in nuclear matter is the so far unknown mechanism of the formation of multinucleon particles (deuterons, tritons, 3He, 4He, ….) with high energies, observed in large numbers in experimental data.
Investigation of nuclear interaction dynamics in several-nucleon systems
The conducted works concern the search for the effects of various components of dynamics (such as the 3-body force, Coulomb interaction, relativistic effects) in three- and four-nucleon systems, investigated in dedicated experiments carried out at the Institute of Nuclear Physics in Groningen (KVI), Forschungszentrum Juelich and implemented currently at the Cyclotron Center Bronowice.