CP violation in a light Higgs boson decay from tau-spin correlations at a linear collider

We present a new method to measure the transverse spin correlation in the $Htotau^+tau^-$ decay. The method has been devised to be insensitive to the beamstrahlung which affects the definition of the beam energy at a linear collider. In the case of two $tautopi^ u$ decays, using the anticipated detector performance of the TESLA project, we get a promising estimation of the error expected on the measurement of a CP violating phase.