In beta decay, the W boson mediates the transformation of a quark into a lepton and its associated neutrino. The W boson is an elementary particle that carries the weak nuclear force, responsible for processes like beta decay.
The W boson's travel distance in beta decay depends on various factors, including the energy of the decay process and the available phase space for the interaction. The precise distance traveled by the W boson is not well-defined or easily measurable, as its existence is fleeting due to its high mass. The W boson typically decays within extremely short distances, typically on the order of 10^−17 meters (known as a "natural length" or "Fermi scale").
After being produced in a beta decay process, the W boson rapidly decays into the lepton and neutrino it is mediating. The resulting lepton and neutrino propagate away from the decay site independently. However, the W boson itself does not travel a significant distance before it undergoes its own decay.