Correlation measurements in Z→ τ+τ− and the τ neutrino helicity

• Published in: Physics letters. B 1994, Vol.321 (1), p.168-176
• Main Authors: Buskulic, D., Goy, C., Crespo, J.M., Creanza, D., de Palma, M., Natali, S., Chai, Y., Xu, D., Xu, R., Boudreau, J., Jacobsen, R., Minten, A., Schlatter, D., Veenhof, R., Wasserbaech, S., Witzeling, W., Bardadin-Otwinowska, M., Falvard, A., Guicheney, C., Henrard, P., Jousset, J., Podlyski, F., Fearnley, T., Hansen, J.R., Nilsson, B.S., Orteu, S., Candlin, D.J., Capon, G., Chiarella, V., Laurelli, P., Murtas, F., Lynch, J.G., Morton, W.T., Smith, M.G., Turnbull, R.M., Brandl, B., Braun, O., Geweniger, C., Putzer, A., Binnie, D.M., Cameron, W., Dornan, P.J., Lieske, N.M., Moutoussi, A., Wright, A.G., Rudolph, G., Bowdery, C.K., Foster, F., Nuttall, M., Sloan, T., Snow, S.W., Greene, A.M., Raab, J., Wolf, B., Calvet, D., Roos, L., Rousseau, D., Talby, M., Dehning, B., Jakobs, K., Schwarz, A.S., St. Denis, R., Wolf, G., Alemany, R., Callot, O., Janot, P., Lefrançois, J., Abbaneo, D., Bagliesi, G., Bottigli, U., Fidecaro, F., Ligabue, F., Steinberger, J., Vannini, C., Venturi, A., Walsh, J., Mir, Ll.M., Clifft, R.W., Thompson, J.C., Bloch-Devaux, B., Lançon, E., Rander, J., Renardy, J.-F., Schwindling, J., Johnson, R.P., Babbage, W., Cartwright, S., Combley, F., Barberio, E., Grupen, C., Rivera, F., Bosisio, L., Gao, Y.S., Nachtman, J.M., Pan, Y.B., Saadi, Y., Scott, I., Sau Lan Wu, Zheng, M., Zobernig, G.
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; General theory of fields and particles; Kinematical properties (helicity and invariant amplitudes, kinematic singularities, etc.); Physics; Relativistic scattering theory; The physics of elementary particles and fields
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/0370-2693(94)90345-X

Using data collected with the ALEPH detector at LEP correlations between the decay products of the τ + and τ − produced in the decay of the Z have been measured. The measurements performed in the decays τ→ πν and τ→ ϱν place limits on deviations from the Standard Model. These are given by the parameter ζ with ζ = −1 for the Standard Model. The measured values are ζ π = −0.95 ± 0.11 ± 0.05 and ζ ϱ = −1.03 ± 0.11 ± 0.05. For models which predict ζ π = ζ ϱ = ζ — interpreted as the average τ neutrino helicity — the measurement is ζ = −0.99 ± 0.07 ± 0.04.