W boson (source code)
= W boson
{c}
{title2=$W^\pm$}
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The W bosons $W^+$ and $W^-$ are massive charged <electroweak gauge bosons> mediating <weak charged currents>. Before mass diagonalization, the charged combinations are $W^\pm=(W^1\mp iW^2)/\sqrt2$; electroweak symmetry breaking gives their tree-level mass $gv/2$.
A W-mediated interaction changes the electric charge of its matter partners. For example, neutron beta decay contains a down-to-up quark transition and an electron–antineutrino pair; at low energy the exchanged W is virtual, not a real emitted particle. A real W produced at high energy can decay to a charged lepton and neutrino or an allowed quark pair. The large W mass explains why low-energy weak processes can be approximated by a short-range <four-fermion interaction>.
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