J/ Y production relative to the reaction plane in Pb-Pb collisions at 158 A GeV/c

1. pions Proj. spect. nucleons x z pions Target spect. nucleons y Y2 x J/Y 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 (g and p0 ) ET • Azimuthal segmentation: 6 (60° wide) sextants • Radial segmentation: 4 rings • Distance from target: 20 cm • Pseudorapidity coverage: 1.1 < lab < 2.3 • Event plane Yn= estimator of the reaction plane  • n = Fourier harmonic • φi = central azimuth of sextant i • ETi = ET in sextant i • weights wi = acceptance correction • defined as <ETtot >/ (6<ETi)> • range between 0.994 and 1.012 (very small correction) • Event plane from pions in backward rapidity region: • Y1 directed along the direction of projectile spectator nucleons • Y2 directed in-plane (i.e. parallel to the reaction plane) • Various methods to estimate event-plane resolution presently under study Signal extraction J/Y reconstruction • J/Y mesons reconstructed from m+m- decay • Muon spectometer acceptance: 2.7 < lab < 3.9 ( 0 < ycm < 1 ) • Background m+m- in J/Y mass range ≈ 5-15% (depending on centrality) • Analyzed statistics: ≈100000 J/Y‘s from year 2000 data taking Analysis and results Results and conclusions Fitting method Counting method • Build mass spectra of dimuons in bins of: • centrality (ET) • azimuthal angle relative to the event plane (DFn=Fdimu-Yn) • 5 component fit to the spectrum • DY, J/Y, Y’, open charm, combinatoria) • Build ET and cos[n(Fdimu-Yn)] spectra of m+m- in 2.9 < M < 3.3 GeV/c2 in bins of azimuthal angle relative to the event plane and subtract • Combin. bck  from Like sign mm in 2.9 < M < 3.3 GeV/c2 • DY  from m+m- in M > 4.2 GeV/c2 • Open Charm  from m+m- in 2.2 < M < 2.6 GeV/c2 Event plane Y1 Event plane Y2 Number of J/Y ’s in bins of ET and azimuthal angle relative to the event plane v1’ and v2’ of J/Y ’s J/Y anisotropy from 2 azim. bins Directed anisotropy Not corrected for event plane resol. • More J/Y‘s in the direction opposite to spectator nucleons  negative J/Y v1 • unexpectedly large BUT momentum conservation effects not taken into account • Event plane not corrected for the momentum taken by the J/Y itself • More J/Y’s exiting in plane  positive J/Y v2 • Probably not due to elliptic flow (i.e. collective motion) • Because charm thermaliztion and J/Y 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/Y break-up by co-moving hadrons Elliptic anisotropy _ _ Not corrected for event plane resol. • Heiselberg, Mattiello, PRC60 (1999) 44902 • Wang, Yuan, PLB540 (2002) 62 • Zhu, Zhuang, Xu, PLB607 (2005) 207