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Measurement of the $\Lambda$ polarization in $\nu_\mu$ charged current interactions in the NOMAD experiment

P. Astier D. Autiero A. Baldisseri M. Baldo-Ceolin M. Banner G. Bassompierre 1 K. Benslama N. Besson I. Bird B. Blumenfeld F. Bobisut J. Bouchez S. Boyd A. Bueno S. Bunyatov L. Camilleri A. Cardini P W. Cattaneo V. Cavasinni A. Cervera-Villanueva A. Chukanov G M. Collazuol G. Conforto C. Conta M. Contalbrigo R. Cousins D. Daniels H. Degaudenzi T. del Prete A. de Santo T. Dignan L. Di Lella E Silva E. Do Couto J. Dumarchez M. Ellis T. Fazio 1 G J. Feldman R. Ferrari D. Ferrere V. Flaminio M. Fraternali J.M. Gaillard 1 E. Gangler A. Geiser D. Geppert D. Gibin S. Gninenko A. Godley J J. Gomez-Cadenas J. Gosset C. Gssling M. Gouanere 1 A. Grant G. Graziani a M. Guglielmi C. Hagner J. Hernando D. Hubbard P. Hurst N. Hyett E. Iacopini C. Joseph F. Juget M. Kirsanov O. Klimov J. Kokkonen A. Kovzelev A. Krasnoperov 1 D. Kustov V. Kuznetsov S. Lacaprara C. Lachaud B. Lakic A. Lanza L. La Rotonda M. Laveder A. Letessier-Selvon J M. Levy L. Linssen A. Ljubicic J. Long A. Lupi A. Marchionni F. Martelli X. Mechain J.P. Mendiburu 1 J P. Meyer M. Mezzetto S R. Mishra G F. Moorhead D. Naumov P. Nedelec 1 Yu. Nefedov C. Nguyen-Mau D. Orestano F. Pastore L S. Peak E. Pennacchio H. Pessard 1 R. Petti A. Placci G. Polesello D. Pollmann A. Polyarush B. Popov C. Poulsen P. Rathouit J. Rico P. Riemann C. Roda A. Rubbia F. Salvatore K. Schahmaneche B. Schmidt T. Schmidt M E. Sevior D. Sillou 1 F J P. Soler Gabriella Sozzi D. Steele U. Stiegler M. Stipcevic T. Stolarczyk M. Tareb-Reyes G N. Taylor S. Tereshchenko A. Toropin a M. Touchard S N. Tovey M T. Tran E. Tsesmelis J. Ulrichs L. Vacavant M. Valdata-Nappi V. Valuev 1 F. Vannucci K E. Varvell M. Veltri V. Vercesi J M. Vieira T. Vinogradova F. Weber T. Weisse F F. Wilson L J. Winton B D. Yabsley H. Zaccone K. Zuber P. Zuccon
Abstract : The $\Lambda$ polarization in $\nu_\mu$ charged current interactions has been measured in the NOMAD experiment. The event sample (8087 reconstructed $\Lambda$'s) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. We observe negative polarization along the $W$-boson direction which is enhanced in the target fragmentation region: $P_x (x_F 0) = -0.21 \pm 0.04 \mbox{(stat)} \pm 0.02 \mbox{(sys)}$. In the current fragmentation region we find $P_x (x_F 0) = -0.09 \pm 0.06 \mbox{(stat)} \pm 0.03 \mbox{(sys)}$. These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. A significant transverse polarization (in the direction orthogonal to the $\Lambda$ production plane) has been observed for the first time in a neutrino experiment: $P_y = -0.22 \pm 0.03 \mbox{(stat)} \pm 0.01 \mbox{(sys)}$. The dependence of the absolute value of $P_y$ on the $\Lambda$ transverse momentum with respect to the hadronic jet direction is in qualitative agreement with the results from unpolarized hadron-hadron experiments.
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Submitted on : Monday, November 20, 2000 - 1:59:54 PM
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P. Astier, D. Autiero, A. Baldisseri, M. Baldo-Ceolin, M. Banner, et al.. Measurement of the $\Lambda$ polarization in $\nu_\mu$ charged current interactions in the NOMAD experiment. Nuclear Physics B, Elsevier, 2000, 588, pp.3-36. ⟨in2p3-00006059⟩

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