The reaction p→n+e++νe is common inside nucleus. But it not considered when we talk about free particle and reason is simply given mass of products being larger than reactants. Now my question is if there is a high energy proton having total energy in order of 2 GeV or let it to be 100 GeV (To even account mass of intermediate W boson) then mass-energy issue should not be in picture. Will then this reaction be possible for proton as free particle. What I think is technically it should be possible as energy and momentum be conserved and all quantum numbers conserved to the extent as inside nucleus. Am I missing something?? If conversion being possible at 100GeV and not at 2 GeV then also suggest how it happens inside nucleus as inside nucleus 100GeV is not possible.