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Measurement of the Michel parameters and the $\nu_{\tau}$ helicity in $\tau$ lepton decays

A. Heister S. Schael R. Barate 1 I. de Bonis 1 D. Decamp 1 C. Goy 1 J P. Lees 1 E. Merle 1 M N. Minard 1 B. Pietrzyk 1 S. Bravo M P. Casado M. Chmeissani J M. Crespo E. Fernandez M. Fernandez-Bosman L. Garrido E. Grauges M. Martinez G. Merino R. Miquel L M. Mir A. Pacheco H. Ruiz A. Colaleo D. Creanza M. de Palma G. Iaselli G. Maggi M. Maggi S. Nuzzo A. Ranieri G. Raso F. Ruggieri G. Selvaggi L. Silvestris P. Tempesta A. Tricomi G. Zito X. Huang Jiali Lin Q. Ouyang T. Wang Y. Xie R. Xu S. Xue J. Zhang L. Zhang D. Abbaneo P. Azzurri G. Boix O. Buchmuller M. Cattaneo F. Cerutti B. Clerbaux G. Dissertori H. Drevermann R W. Forty M. Frank T C. Greening J B. Hansen J. Harvey P. Janot B. Jost M. Kado P. Mato A. Moutoussi F. Ranjard L. Rolandi D. Schlatter O. Schneider P. Spagnolo W. Tejessy F. Teubert E. Tournefier J. Ward Ziad Ajaltouni 2 F. Badaud 2 Alain Falvard 2 Pascal Gay 2 Pierre Henrard 2 J. Jousset 2 B. Michel 2 S. Monteil 2 Jean-Claude Montret 2 D. Pallin 2 Pascal Perret F. Podlyski 2 J D. Hansen J R. Hansen P H. Hansen B S. Nilsson A. Waananen A. Kyriakis C. Markou E. Simopoulou A. Vayaki K. Zachariadou A. Blondel 3 G. Bonneaud J C. Brient A. Rouge 3 M. Rumpf 3 M. Swynghedauw 3 M. Verderi 3 H. Videau 3 V. Ciulli E. Focardi G. Parrini A. Antonelli M. Antonelli G. Bencivenni G. Bologna F. Bossi P. Campana G. Capon P. Laurelli G. Mannocchi F. Murtas G P. Murtas L. Passalacqua M. Pepe-Altarelli A Halley J G. Lynch P. Negus V. O'Shea C. Raine a S. Thompson S R. Wasserbaech R. Cavanaugh S. Dhamotharan C. Geweniger P. Hanke G. Hansper V. Hepp E E. Kluge A. Putzer K. Tittel S. Werner M. Wunsch R. Beuselinck D M. Binnie W. Cameron P J. Dornan M. Girone N. Marinelli J K. Sedgbeer J C. Thompson V M. Ghete P. Girtler E. Kneringer D. Kuhn G. Rudolph E. Bouhova-Thacker C K. Bowdery a J. Finch F. Foster G. Hughes R W L. Jones M R. Pearson N A. Robertson I. Giehl K. Jakobs K. Kleinknecht G. Quast B. Renk E. Rohne H G. Sander H. Wachsmuth C. Zeitnitz A. Bonissent 4 J. Carr 4 P. Coyle 4 O. Leroy 4 P. Payre 4 D. Rousseau 4 M. Talby 4 M. Aleppo F. Ragusa A. David H. Dietl G. Ganis K. Huttmann G. Lutjens C. Mannert W. Manner H G. Moser R. Settles H. Stenzel W. Wiedenmann G. Wolf J. Boucrot 5 O. Callot 5 M. Davier 5 L. Duflot 5 J F. Grivaz 5 P. Heusse 5 A. Jacholkowska 5 J. Lefrancois 5 J J. Veillet 5 I. Videau 5 C. Yuan 5 G. Bagliesi T. Boccali L. Foa A. Giassi F. Ligabue A. Messineo F. Palla G. Sanguinetti A. Sciaba G. Sguazzoni R. Tenchini A. Venturi P G. Verdini G A. Blair G. Cowan M G. Green T. Medcalf A. Misiejuk J A. Strong P. Teixeira-Dias J H. von Wimmersperg-Toller R W. Clifft T R. Edgecock I R. Tomalin B. Bloch-Devaux P. Colas S. Emery W. Kozanecki E. Lancon M C. Lemaire E. Locci P. Perez J. Rander J F. Renardy A. Roussarie J P. Schuller J. Schwindling B. Vallage N. Konstantinidis a M. Litke G. Taylor C N. Booth S. Cartwright F. Combley M H. Lehto L F. Thompson K. Affholderbach A. Bohrer S. Brandt C. Grupen A. Ngac G. Prange U. Sieler G. Giannini J E. Rothberg S R. Armstrong K. Cranmer P. Elmer Y. Gao S. Gonzalez O J. Hayes H. Hu S. Jin J. Kile P A. Mcnamara J. Nielsen W. Orejudos y B. Pan Y. Saadi I J. Scott J. Walsh S L. Wu X. Wu G. Zobernig
Abstract : A measurement of the Michel parameters and the average $\nu_\tau$ helicity in $\tau$ lepton decays is described. The data was collected with the ALEPH detector at LEP during the years 1991 to 1995. A total integrated luminosity of 155\,$\text{pb}^{-1}$ is analysed. The Michel parameters $\rho_l$, $\xi_l$, $(\xi\delta)_l$ ($l=e,\mu$), and $\eta_\mu$ are determined for the leptonic deca ys, and the chirality parameters $\xi_\pi$, $\xi_\rho$, and $\xi_{a_1}$ for the hadronic final states. Under the assumptions of $e$\bis $\mu$ universality and $\xi_\pi=\xi_\rho=\xi_{a_1}$, the values $\rho_l=0.742\pm 0.016, \eta_l=0.01 2\pm 0.026,\break (\xi\delta)_l=0.776\pm 0.051, \xi_l=0.986\pm 0.074$, and $\xi_h=0.992\pm 0.011$ are obtained. No significant deviation is observed from the Standard Model assumption of the \ vma{} structure of the charged weak interaction.
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A. Heister, S. Schael, R. Barate, I. de Bonis, D. Decamp, et al.. Measurement of the Michel parameters and the $\nu_{\tau}$ helicity in $\tau$ lepton decays. European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2001, 22, pp.217-230. ⟨in2p3-00010979⟩

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