No protons needed? Possible discovery of a four-neutron particle

The reaction which may have produced a tetraneutron (seen in the bottom middle). The reaction begins with two forms of helium which become beryllium and a tetraneutron. The beryllium then decays into alpha particles (helium nuclei). (credit: APS/Alan Stonebraker)

It’s tempting to call the tetraneutron a theoretical particle, as its existence has yet to be confirmed. But that would imply that it’s a consequence of some existing theoretical model, that it’s predicted by some theory. The tetraneutron, however, contradicts the relevant theories—it should be impossible.

And yet, amidst all the (deserved) excitement for the detection of gravitational waves last week, an experiment quietly turned up the strongest evidence for a tetraneutron thus far. It’s not full confirmation yet, but if the new study’s conclusions are borne out, things are going to get weird.

The Story So Far

The troublesome particle may have first appeared in 2001 after decades of speculation and a few doubtful experiments. Researchers fired beryllium-14 atoms at a carbon target to observe the resulting chaos of particles, a relatively common practice.

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