An international team of scientists has conducted the most precise measurements to date of CP symmetry breaking in hyperon decays. Researchers from the National Centre for Nuclear Research (NCBJ) — dr Varvara Batozskaya and Prof. Andrzej Kupść — made key contributions to the analysis.

The research findings were published on May 18 in the journal Physical Review Letters, DOI: https://doi.org/10.1103/c1fz-9r8q 

One of the greatest mysteries in physics is the discrepancy between the amount of matter and antimatter in the universe and what caused it. Currently, the best explanation is offered by Andrei Sakharov’s theory of so-called baryogenesis, which postulates, among other things, the existence of interactions that break CP symmetry. This principle states that particles should behave identically to their antiparticles (C) reflected in a mirror (P).

Scientists are particularly interested in studying the violation of this symmetry by baryons, which also allows for testing the validity of the Standard Model — the theory describing fundamental interactions and particles. A group of researchers from the BESIII experiment in China paid particular attention to the decay of Xi hyperons – particles containing two strange quarks (s). This decay into a final proton occurs in two steps, allowing for a unique measurement of the rotation angle of the baryon spin vector.

To determine whether CP symmetry was broken during their decay, it was necessary to very precisely determine individual decay parameters, such as the strong and weak phase differences. A new data analysis, to which dr Varvara Batozskaya and Prof. Andrzej Kupść from the High Energy Physics Division of the National Centre for Nuclear Research (NCBJ) made key contributions, allowed for results of unprecedented precision.

The analysis was conducted using an original method developed by Professor Kupść and his colleagues (Phys.Rev.D 99 (2019) 5, 056008 i Phys.Rev.D 100 (2019) 11, 114005). Dr Batozskaya acted as the coordinator for the new study.

A comparison of the results obtained with the values predicted by the Standard Model did not provide any grounds for suspecting a violation of CP symmetry in the process under study. – All results were consistent with previous findings from the BESIII data. What is significant, however, is that the eightfold increase in the dataset allowed us to determine the parameters with much greater precision. For example, we determined the values for the weak phase with the highest accuracy among the baryon decays studied to date – explains dr Varvara Batozskaya.

More precise results will only be possible thanks to new facilities that will provide researchers with significantly larger amounts of experimental data. The current work will serve as a foundation for them, which may make it possible to conclusively determine why our Universe has been dominated by matter from the very beginning.