Tau Polarization in Tau-Neutrino Nucleon Scattering

We investigate the spin polarization of τ leptons produced in ντ and ν̄τ nucleon scattering via charged currents. Quasi-elastic scattering, ∆ 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’s 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. KEK-TH-887 KOBE-FHD-03-01 HUPD-0303 hep-ph/0305324 May 2003 E-mail address: [email protected] E-mail address: [email protected]