Collisions hint that four neutrons form a transient isolated entity
Nature, Published online: 22 June 2022; doi:10.1038/d41586-022-01634-x
An experiment firing helium-8 nuclei at a proton target has generated evidence that four neutrons can exist transiently without any other matter. But doubts remain, because the existence of such systems is at odds with theory.
Source: Nature