A visit to an extreme-conditions laboratory

“The CBM (Compressed Baryonic Matter) experiment being conducted at FAIR is one of the most ambitious projects in contemporary nuclear and dense-matter physics,” says Prof. Hanna Zbroszczyk, a researcher specialising in heavy-ion physics and coordinator of the GET_INvolved programme, which enables WUT students to complete internships at the centre in Germany. “Its aim is to study strongly interacting matter under extreme conditions of density and temperature - conditions found inside neutron stars and during their mergers, as well as in the early Universe,” the WUT physicist adds.

Unlocking the secrets of neutron-star interiors

The team from the WUT Faculty of Physics – comprising students, doctoral students and researchers – is particularly involved in the correlation femtoscopy measurement programme. This involves analysing correlations between particles recorded by the detector, making it possible to study interactions over distances on the order of a femtometre, comparable to the size of an atomic nucleus.

The research focuses on strong interactions. The shape of correlation functions for different particle pairs can reveal information about interaction potentials, their ranges, and the strength of attraction or repulsion in dense baryonic matter. The resulting data on baryon–baryon interactions are essential for constructing realistic models of the equation of state of the matter that makes up neutron stars. Indirectly, this also informs the interpretation of astrophysical observations, including neutron-star masses, radii and deformabilities.

“The experiments conducted at FAIR and GSI will be unique because they will probe strong interactions across precisely the range of densities and energies expected inside neutron stars and during neutron-star mergers. The earlier HADES experiment, conducted at lower beam energies, demonstrated that matter with parameters similar to those found in neutron stars can be reproduced under laboratory conditions. CBM will be a natural continuation and extension of this programme,” explains Prof. Zbroszczyk.

A student contribution

Kinga Urban had the opportunity to take part in the HADES experiment while completing a summer internship under the GET_INvolved programme.

“Strong interactions are still not fully understood. The experiment focuses on producing the high-density, low-temperature matter found inside neutron stars, allowing us to gain a better understanding of these interactions. My task was to analyse data from the detectors, enabling measurements of the spatial and temporal parameters of the emission source of particles produced in collisions. Alongside this work, I was able to make time for visits to GSI laboratories and attend lectures by specialists in plasma physics, atomic physics, relativistic radioactive-beam research and neutron detection. There was also room for interests outside science. A music group operates at GSI, and I joined it,” recalls Kinga Urban, who works under Prof. Zbroszczyk’s supervision.

Kinga was joined by three other technical physics students – Jan Bogdański, Anna Kodym and Kacper Zięba – as well as doctoral student Arkadip Mukherjee and two staff members affiliated with the Division of Nuclear Physics: Daniel Wielanek, PhD, and Somen Gope, PhD.

“It is their day-to-day work – from designing and testing detectors and developing software to conducting detailed data analyses – that turns the unique capabilities of the CBM and HADES experiments into tangible progress in our understanding of the fundamental properties of matter and the nature of the Universe,” emphasises Prof. Zbroszczyk.

Research and leadership

The Faculty of Physics team not only participates in measurements, but also serves on the experiments’ decision-making bodies. Its researchers chair the CBM and HADES Collaboration Boards and coordinate the CBM/HADES pillar nationally, ensuring the coherence of the research programme, the quality of analyses and the effective use of the equipment’s capabilities. The Polish research community is boldly setting the direction for research into dense baryonic matter and strong interactions.

Technological commissioning of the FAIR accelerator complex in Darmstadt is scheduled for late 2028. It will mark the culmination of a multi-stage process of testing the cryogenic infrastructure and integrating FAIR’s control systems. A key moment in this phase will be the delivery of the first stable ion beam from the newly built SIS100 ring synchrotron directly to the CBM detector’s experimental area, formally launching the global research programme on dense baryonic matter.