Neutrino helicity
= Neutrino helicity
{title2=$h_\nu=2\mathbf S_\nu\cdot\widehat{\mathbf p}_\nu$}
For a relativistic <neutrino>, the normalized <helicity> is approximately $-1$ in ordinary weak production. For a massive particle, <helicity> and <fermion chirality> differ; suppressed opposite-helicity amplitudes and frame dependence prevent promoting the massless selection rule to an exact statement about arbitrary boosts.