Measurement of Tau Polarization in W->tau nu Decays with ATLAS

Tau polarization is measured in the hadronic tau decays in W->tau nu decays. The data, corresponding to an integrated luminosity of 24 pb^-1, were collected by the ATLAS experiment in the year 2010. The measured value of the tau polarization is P_tau= -1.06\; \pm 0.04\;(stat)\; ^{+0.05}_{-0.07}\;(syst), in agreement with the Standard Model predictions, and is consistent with a physically allowed 95% credibility interval [-1,-0.91]. This result marks the first measurement of tau polarization at a hadron collider as well as the first such measurement in W->tau nu decays. Tau polarization is a powerful probe of potential new phenomena at the Large Hadron Collider. Applications include sensitivity to the nature of the spin of a theorized Higgs boson that decays to tau pairs.