Tau neutrino (${\nu }_{\tau }$)

The neutrino flavor associated with the tau lepton in the weak charged current. Its direct detection through interactions producing a tau lepton was announced by the DONUT experiment in 2000.^[ref]

For a nearly massless incident tau neutrino and stationary target of mass $M_T$, the initial Mandelstam variables give $s=M_T^2+2M_T{E}_{\nu }$. At threshold the final tau lepton and the lightest allowed recoil system have no relative momentum, so $s=(m_{\tau }+M_X{)}^2$. This proves the formula. A free neutron recoil channel gives approximately $3.45\mathrm{GeV}$; an electron target has a different recoil and a threshold near $3.09\mathrm{TeV}$.

The antiparticle associated with the tau-flavour neutrino. A tau lepton of positive charge emits it in an ordinary charged current decay; a negative tau lepton instead emits a tau neutrino.

A Fermilab experiment that directly observed tau neutrino charged current interactions using nuclear emulsion and a prompt neutrino beam from an $800\mathrm{GeV}$ proton dump. Ds meson decays and the subsequent tau lepton decays supply the main tau-flavour component.