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Published byRichard Parsons Modified over 9 years ago
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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 22 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
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