The polarimeter vector for τ → 3πν_τ decays

The polarimeter vector of the τ represents an optimal observable for the measurement of the τ spin. In this paper we present an algorithm for the computation of the τ polarimeter vector for the decay channels τ^- → π^- π^+ π^- ν_τ and τ^- → π^- π^0 π^0 ν_τ. The algorithm is based on a model for the hadronic current in these decay channels, which was fitted to data recorded by the CLEO experiment [1].