298 articles – 2328 Notices  [english version]
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3rd International Conference On Hard And Electromagnetic Probes Of High-Energy Nuclear Collisions (HP2008), Illa da Toxa : Espagne (2008)
J / ψ azimuthal anisotropy relative to the reaction plane in Pb-Pb collisions at 158 GeV per nucleon
F. Prino, B. Alessandro, C. Alexa, R. Arnaldi, M. Atayan, S. Beolè, V. Boldea, P. Bordalo, G. Borges, C. Castanier1, J. Castor1, B. Chaurand2, B. Cheynis3, E. Chiavassa, C. Cicalò, M. P. Comets4, S. Constantinescu, P. Cortese, A. De Falco, N. de Marco, G. Dellacasa, A. Devaux1, S. Dita, J. Fargeix1, P. Force1, M. Gallio, C. Gerschel, P. Giubellino, M. B. Golubeva, A. A. Grigoryan, S. Grigoryan, F. F. Guber, A. Guichard3, H. Gulkanyan, M. Idzik, D. Jouan4, T. L. Karavicheva, L. Kluberg2, A. B. Kurepin, Y. Le Bornec4, C. Lourenço, M. Mac Cormick4, A. Marzari-Chiesa, M. Masera, A. Masoni, M. Monteno, A. Musso, P. Petiau2, A. Piccotti, J. R. Pizzi3, G. Puddu, C. Quintans, L. Ramello, S. Ramos, L. Riccati, H. Santos, P. Saturnini1, E. Scomparin, S. Serci, R. Shahoyan, F. Sigaudo, M. Sitta, P. Sonderegger, X. Tarrago4, N. S. Topilskaya, G. L. Usai, E. Vercellin, L. Villatte4, N. Willis4, T. Wu4
NA50 Collaboration(s)

The J/ψ azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed J/ψ mesons at SPS energies. Hence, the measurement of J/ψ elliptic anisotropy, quantified by the Fourier coefficient v 2 of the J/ψ azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous J/ψ suppression observed in Pb-Pb collisions. We present the measured J/ψ yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient v _{2} as a function of the collision centrality and of the J/ψ transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or p_{T} sub-samples. The extracted v_{ 2} values are significantly larger than zero for non-central collisions and are seen to increase with p_{T}
1 :  LPC - Laboratoire de Physique Corpusculaire [Clermont-Ferrand]
2 :  LLR - Laboratoire Leprince-Ringuet
3 :  IPNL - Institut de Physique Nucléaire de Lyon
4 :  IPNO - Institut de Physique Nucléaire d'Orsay
Physique/Physique Nucléaire Expérimentale