Physics news on the Internet: January 2024

T Faestermann (Technical University of Munich, Germany) and his co-authors have performed an experiment [1] where the bound state of four neutronsÐa tetraneutron nÐwas observed, perhaps for the first time. It has been sought (together with n and n) since the 1960s, and some indications of the occurrence of candidate events for n have been obtained. These results remained, however, ambiguous. In the new experiment, a beam of 7Liÿ ions obtained at the accelerator in Garching (Germany) was directed to an Li2O oxide target sputtered onto lithium foil, and the reactions Li(Li,C)4n were analyzed. The energy spectrum of C nuclei escaping at angles of 6ÿ9:5 was investigated using a wire proportional counter and an array of silicon detectors. With a 3s significance, a peak was revealed, which can be interpreted as a C nucleus in the first excited state and n with a binding energy of 0.42(16)MeV and a half-life of 450 s. An alternative hypothesis that the four escaping electrons are not bound cannot be ruled out yet, but the authors of this study believe that this possibility is less probable, because the observed peak in the spectrum is much narrower than it should be in this case. The reaction Li(Li,C)4n was already examined earlier at the Kurchatov Institute [2], but at higher energies, due to which the presence of the bound state of n could not be found.