While all atomic nuclei except hydrogen are composed of protons and neutrons, physicists have been searching for a particle consisting of two, three or four neutrons for over half a century. Experiments by a team of physicists of the Technical University of Munich (TUM) at the accelerator laboratory on the Garching research campus now indicate that a particle comprising four bound neutrons may well exist.
Click here for original story, Experiment finds evidence for a long-sought particle comprising four neutrons
Source: Phys.org