Mugaliens. The mechanism for neutron decay involves a quark identity change. Any time any particle changes it's identity, that's a form of the weak interaction, so the W-boson is involved....(there are also other weak interactions).
The down quark flips to an up, and emits a W- simultaneously. The W- is short-lived and decays almost instantly to an electron-type antineutrino, and an electron. The "new" up quark is bound with the other up, and the remaining down, in the proton. The antineutrino escapes to join the ambient neutrino sea....(physicists use the word "neutrino" loosely sometimes to refer to either type...). The electron is captured by the proton to make monatomic protium.....which will join with another to make diatomic hydrogen, eventually.

pete

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A third rate theory forbids
A second rate theory explains after the fact
A first rate theory predicts...A. Lomonosov