Mystery dark matter may be ordinary neutrons that have decayed

Dark matter makes up a lot of the universe, but we still don’t know what it is. Could it be neutrons decaying into strange particles that shun normal matter?

The humble neutron could be hiding a deep, dark secret. For 20 years, two experiments that measure the lifetime of a neutron have been at odds. Now it seems that disconnect may be the result of neutrons occasionally decaying into particles of dark matter, the stuff that is thought to make up most of the unseen mass of the universe.

“What we thought were our most likely ideas for what dark matter might be, none of those have worked,” says Dan Hooper at Fermilab near Batavia, Illinois, who wasn’t involved in the research. “It seems well worthwhile to consider the seemingly unlikely ideas.”

We know that a neutron can morph into a proton in a process called beta decay, which also spits out an electron and an antineutrino.

The “beam experiment” involves counting the number of protons produced by a