Tau polarization in tau-neutrino nucleon scattering

We investigate the spin polarization of tau(+/-) leptons produced in v(tau) and v(tau) nucleon scattering via charged currents. Quasi-elastic scattering, Delta resonance production and deep inelastic scattering processes are studied. The polarization information is essential for measuring the tau(+/-) appearance rate in long baseline neutrino oscillation experiments, because the decay particle distributions depend crucially on the tau(+/-) 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 tau(+/-)'s have high degree of polarization, and their spin direction depends non-trivially on the energy and the scattering angle of tau(+/-) in the laboratory frame. (C) 2003 Elsevier B.V. All rights reserved.