Z boson

The Z boson is the massive neutral electroweak gauge boson mediating the weak neutral current. In the standard tree-level mixing convention, $Z_{\mu }=(g{W}_{\mu }^3-g^{\prime }{B}_{\mu })/\sqrt{g^2+g^{\prime 2}}$ and $m_Z=v\sqrt{g^2+g^{\prime 2}}/2$.

Its interactions need not change a particle's electric charge. Neutrino scattering through Z exchange can therefore transfer energy to a target without producing a charged lepton of the neutrino flavor. A real Z can decay to charged fermion pairs or neutrino pairs when kinematically allowed. The latter contribute an invisible decay width, so the measured total and visible widths constrain invisible final states. Neutrality alone does not make the Z photon-like: its mass, chiral couplings and short-range low-energy effect differ.