In this paper, a measurement of tau polarization in W -> tau nu decays is presented. It is measured from the energies of the decay products in hadronic tau decays with a single final state charged particle. The data, corresponding to an integrated luminosity of 24 pb(-1), were collected by the ATLAS experiment at the Large Hadron Collider in 2010. The measured value of the tau polarization is P-tau = -1.06 +/- 0.04 (stat)(-0.07)(+0.05) (syst), in agreement with the Standard Model prediction, and is consistent with a physically allowed 95 % CL interval [-1,-0.91]. Measurements of tau polarization have not previously been made at hadron colliders.
Aad, G., Abbott, B., Abdallah, J., Khalek, S.a., Abdelalim, A.a., Abdesselam, A., et al. (2012). Measurement of tau polarization in W -> tau nu decays with the ATLAS detector in pp collisions at root s=7 TeV. THE EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS, 72(7), 2062.1-2062.21 [10.1140/epjc/s10052-012-2062-6].