Tau polarization in tau-neutrino nucleon scattering Original Research Article

We investigate the spin polarization of τ± leptons produced in ντ and ν̄τ nucleon scattering via charged currents. Quasi-elastic scattering, Δ resonance production and deep inelastic scattering processes are studied. The polarization information is essential for measuring the τ± appearance rate in long baseline neutrino oscillation experiments, because the decay particle distributions depend crucially on the τ± spin. In this article, we calculate the spin density matrix of each process and estimate the spin polarization vector in medium and high neutrino energy interactions. We find that the produced τ±ʹs have high degree of polarization, and their spin direction depends non-trivially on the energy and the scattering angle of τ± in the laboratory frame.