It is with great sadness that we inform you that on 17 March 2020.
Jacek Rożynek, PhD,
employee of the Department of Theoretical Physics at the NCBJ Department of Fundamental Research,
scientist, populariser and an uncommonly cheerful person.

We will miss him greatly!

Management and Scientific Council
of the National Centre for Nuclear Research
Friends, Colleagues

Funeral services will be held on 27 March at 2.00 p.m. at North Cemetery (Wólka Węglowa)
of which notice is hereby given by the bereaved
wife, daughter and son.
In the current situation of an epidemic, it is only in our thoughts that we can unite with the bereaved family.

Jacek Zygmunt Rożynek was born on 21 June 1951 in Poznań. His parents Marian Rożynek and Danuta Rożynkowa, née Piekarska, worked at the Medical Academy in Poznań. His father, a graduate of the Humboldt University in Berlin, was scientifically engaged in anatomopathology, and his mother undertook research in genetics after graduating from the Poznan Medical Academy. Jacek's younger siblings were also born in Poznań, brother Andrzej in 1952 and sister Marysia in 1956. In 1963, his father became head of the Chair and Department of Clinical Pathomorphology at the Medical Academy in Lublin. In 1965, the family moved to Lublin. Danuta Rożynkowa was employed at the Medical Academy and set up the Human Genetics Laboratory, which she headed until her retirement. Jacek's parents obtained professorships and worked at the Medical Academy even when retired.

The 14-year-old Jacek was not happy about the change of residence, as he felt comfortable at school in Poznań and had many friends there. In Lublin, he graduated from the Stanisław Staszic secondary school and went on to study at the Faculty of Mathematics, Physics and Chemistry at the Maria Curie-Skłodowska University.

After graduation, Jacek moved to Warsaw and took up a job as a high school physics teacher. At the same time, he started working with Professor Janusz Dąbrowski, one of the outstanding nuclear theoretical physicists working at the Theoretical Department of the Institute of Nuclear Research. The 1970s were a time of flourishing theoretical and experimental research on the strange particles discovered three decades earlier. Researchers were interested in the puzzles of their structure and interaction, particularly in the situation of their co-formation of exotic atomic nuclei. The latter topic had just become the subject of a very fruitful collaboration between Jacek and Professor Dąbrowski. Colleagues who remember their collaboration agree that Jacek was an ideal collaborator for Professor Dąbrowski: interested in the subject, hard-working, enthusiastic and optimistic. This must have brought results. Significant publications were produced, the most famous of which, "Energy and Width of Σ Hyperon in Nuclear Matter", published in the dramatic year of 1981, which was very important for the history of Poland, received a huge number of citations. Jacek was employed at the Theoretical Department of the Institute of Nuclear Research, where he obtained further scientific degrees and worked until the day of his tragic death.

Jacek was able to talk interestingly about basically everything and was genuinely interested in many issues. This openness, curiosity and insight not only facilitated his ability to build new interpersonal contacts, but also encouraged him to take up new research challenges together with colleagues inside and outside the institute. One of the topics he took up was the so-called EMC effect - a phenomenon observed at CERN in 1983 and still puzzling to this day, in which the probability (physicists measure it by a quantity called the active cross-section) of a deeply inelastic scattering of electrons and other leptons on a system of many protons and neutrons bound into an atomic nucleus is unexpectedly smaller than the sum of the probabilities of similar scattering occurring on free protons and neutrons. Just a few months after observing this effect, Jacek and his co-workers published the first paper attempting to explain it theoretically and returned to the issue several more times in the following years.

Jacek was curious to observe what his colleagues were doing. He was able to see the connection between seemingly distant issues, and it happened that this insight inspired him to do more in-depth research. Such was the case with his interest in non-extensive statistics, which was being dealt with at Hoża by Professor Grzegorz Wilk, who collaborated with the originator of this approach, Professor Constantino Tsallis. Their discussions together made it clear to Jacek and his fellow researchers that this alternative statistics could be applied to the description of nuclear matter, which Jacek knew very well. The researchers saw that Tsallis' non-extensive statistics allowed for a very economical description of the conditions under which the production of such nuclear matter occurs. Through a series of significant papers, the last of which is yet to be published, Jacek became a well-known and recognised expert in the non-extensive description of nuclear and quark-gluon matter.

Jacek was also not entirely lacking in his own ambitious and daring ideas. One of these was the new idea of describing the so-called symmetry energy in nuclei and nuclear matter. He proposed a new description of neutron stars using the resulting equation of state from his research. In discussions, he also considered the possibility of including non-extensive effects. Unfortunately, he would not be given the opportunity to bring this idea to fruition.

Jacek was not only curious about the world, but was also able to infect others with his curiosity and enthusiasm. These included his colleagues from the institute and the university, people he met at conferences and in private situations, and last but not least children and young people, for he was an excellent but special populariser. He did not write popular science articles, he did not appear in the media, but he did what he did best - he made that endearing, direct, warm contact of his and talked, and showed, and explained, and listened, and tried to understand what his interlocutor might have a problem with. For several years he hosted and co-hosted events of science festivals and picnics. The famous and several times nationally and internationally awarded 'Physical Sandbox' for the youngest - even for children of a few years old, was his undeniable achievement. By demonstrating and explaining simple experiments - often invented by himself - he won the hearts of the youngest children, as well as the parents assisting them. When he sat face to face with the young explorers of the laws of nature, nothing was too difficult or impossible anymore. His warm smile melted away all barriers - even language barriers.

Jacek was like this in every situation: at a conference, at a picnic, over coffee at the institute, in the library... Always helpful, always ready to listen and to have an interesting conversation, kind, sensitive, someone who saw a lot and understood even more. He won everyone over with his openness and kindness, cheerfulness, sense of humour and wit. Jacek did not judge, criticise or try to change people. He seemed to understand, accept and simply like us all. And it was impossible not to like Jacek.

In 1989, Jacek married Anna Okopińska. They were united not only by their love of scientific work in the field of physics, but also by their passions and ways of spending their free time - visiting interesting places in Poland, travelling around Europe and especially hiking in various mountains of the world. Their daughter Zuzanna Kinga Rożynek was born in 1989 and their son Filip Marian Rożynek in 1994. Jacek was passionate about classical music. He amassed an extensive collection of vinyl records and played with great passion himself almost every day on the Bechstein piano he inherited from his aunt. He passed on his love of music to his daughter, who continues to collect records. Zuzia graduated from music school and often plays this piano beautifully.

Dr. Jacek Rożynek is remembered by Prof. Dr. Grzegorz Wilk

I do not remember, unfortunately, when and under what circumstances Jacek Rożynek appeared at our ZdP8 IPJ. I only remember that he worked closely with Prof. J. Dąbrowski in his programme for the description of nuclear matter, while I was involved in the phenomenology of strong interactions. I also remember that we established contacts quite quickly, discussing various topics. It turned out that Jacek could talk interestingly about almost anything, which we often did. He was also very helpful in solving all kinds of computing and day-to-day problems with our then modest computing facilities.

He was also open-minded about other issues, which soon led us to begin our collaboration on the study of the so-called "EMC effect", i.e. the significant deviation from expectations of the then newly observed results in lepton collisions on atomic nuclei. This resulted in a paper in Phys. Rev D in 1984 and a couple of conference presentations. This idea was later replicated in many papers by other authors, and we returned to subsequent versions of it twice more (in 2000 with a paper in Phys. Lett. B and in 2005 with a paper in Phys. Rev. C). Since for both of us this topic, although very interesting, was rather a side issue, we did not pursue it further and Jacek continued his research into nuclear matter.

When I took up the so-called non-extensive statistics, we very quickly realised that it was worthwhile to apply it to the description of nuclear matter, because it allows a very economical description of the conditions under which the production of such matter occurs. This was already 2008. This idea proved to be very successful and resulted in 4 publications in 2009 in J. Phys. G and 2 in 2016 2 in Eur. Phys. J. A - which became the basis for Jack's habilitation dissertation.

This continued with a fourth fourth publication in Symmetry-Basel in 2019 and several conference presentations. The most recent was an invited paper that Jacek gave at the Ettore Majorana Foundation and Centre for Scientific Culture, International School on Complexity - XVI Course; Nonextensive Statistical Mechanics, Superstatistics and Beyond: Theory and Applications in Astrophysical and other Complex Systems; July 2-8, 2019 Erice, Italy. Its development will be published shortly in Eur. Phys. J. - Special Topics. These latter topics, and especially the recent conference he attended, have made him a well-known and recognised expert in the field of non-extensive description of nuclear and quark-gluon matter.

Recently, Jacek has been intensively developing his new idea of describing the so-called symmetry energy in nuclei and nuclear matter. The aim was very ambitious - a new description of neutron stars using the resulting equation of state (and possibly including non-extensive effects as well). Unfortunately, the almost completed work, which was constantly revised and improved, will no longer live to see publication.

Jack's passing has been received in the nuclear matter research community with great sadness and regret, as evidenced by letters I have received from Prof Airton Deppman, Andrea Rapisardo and Constantino Tsallis. Our plans to further develop this field at NCBJ will unfortunately no longer materialise.

Memories and Condolences

Jacek was an extraordinary Populariser!