The neutron's phase transition to its "decay" particles presented a unique challenge during its derivation. It and many other transformations such as the muon to muon neutrino, electron and anti-neutrino phase change can only take place if there is also an additional virtual pion (gluon) created which balances the "phase transformation" books. Logically thinking this through, we note that particle decay patterns are deduced by inference, not by being able to actually see the actual particles themselves. Might it not be the case that within experimental error of the huge (91 GeV) energy of W Bosons, the presence of a small instantaneously created and destroyed particle with a near-infinitesimally small lifetime could, perchance, have been overlooked?
There is however a potential way to infer the possible existence of this additional intermediary. Currently below experimental and statistical error levels, more accurate resolution of future experiments may reveal a discrepancy in the originating points of the "decay" particles from the W Boson and of the anti-neutrino and the electron.