1. Results and conclusions Signal extraction J/  production relative to the reaction plane in Pb-Pb collisions at 158 A GeV/c Francesco Prino (INFN – Sezione di Torino) for the NA50 collaboration Reaction plane estimation Electromagnetic calorimeter  Made of Pb and scintillating fibers  Measures neutral (  and  0 ) E T  Azimuthal segmentation: 6 (60° wide) sextants  Radial segmentation:4 rings  Distance from target:20 cm  Pseudorapidity coverage:1.1 <  lab < 2.3 z x Proj. spect. nucleons Target spect. nucleons pions J/  reconstruction J/  mesons reconstructed from  +  - decay  Muon spectometer acceptance:2.7 <  lab < 3.9 ( 0 < y cm < 1 )  Background  +  - in J/  mass range ≈ 5-15% (depending on centrality)  Analyzed statistics: ≈100000 J/  ‘s from year 2000 data taking Number of J/  ’s in bins of E T and azimuthal angle relative to the event plane  Build E T and cos[n(  dimu -  n )] spectra of  +  - in 2.9 < M < 3.3 GeV/c 2 in bins of azimuthal angle relative to the event plane and subtract Combin. bck  from Like sign  in 2.9 < M < 3.3 GeV/c 2 DY  from  +  - in M > 4.2 GeV/c 2 Open Charm  from  +  - in 2.2 < M < 2.6 GeV/c 2 Event plane  n = estimator of the reaction plane   n = Fourier harmonic  φ i = central azimuth of sextant i  E T i = E T in sextant i  weights w i = acceptance correction defined as / (6 range between 0.994 and 1.012 (very small correction) Event plane from pions in backward rapidity region:   1 directed along the direction of projectile spectator nucleons   2 directed in-plane (i.e. parallel to the reaction plane) Various methods to estimate event-plane resolution presently under study  Build mass spectra of dimuons in bins of: centrality (ET) azimuthal angle relative to the event plane (  n =  dimu -  n )  5 component fit to the spectrum DY, J/ ,  ’, open charm, combinatoria) Analysis and results v 1 ’ and v 2 ’ of J/  ’s More J/  ‘s in the direction opposite to spectator nucleons  negative J/  v 1  unexpectedly large BUT momentum conservation effects not taken into account Event plane not corrected for the momentum taken by the J/  itself More J/  ’s exiting in plane  positive J/  v 2  Probably not due to elliptic flow (i.e. collective motion) Because charm thermaliztion and J/  formation from recombination are not likely to occur at SPS energies  Consequence of anisotropic cc absorption in the medium: cc dissociation by hard gluons in the QGP phase J/  break-up by co-moving hadrons Fitting method Counting method E T range (GeV) N reco (J/  ) along  1 N reco (J/  ) opposite  1 10-3086009300 30-501020011100 50-701040011100 70-90990010100 90-1201060011000 E T range (GeV) N reco (J/  ) in plane N reco (J/  ) out of plane 10-3091008900 30-501070010500 50-701070010800 70-90103009700 90-1201090010700 J/  anisotropy from 2 azim. bins x y 22 Directed anisotropy Elliptic anisotropy _ _  Heiselberg, Mattiello, PRC60 (1999) 44902  Wang, Yuan, PLB540 (2002) 62  Zhu, Zhuang, Xu, PLB607 (2005) 207 Not corrected for event plane resol. Event plane  1 Event plane  2