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А.Б.Курепин – ИЯИ РАН, Москва

Столкновение релятивистских тяжелых ядер и загадка чармония. А.Б.Курепин – ИЯИ РАН, Москва. VI Марковские чтения 15 Мая 2008 г. ОИЯИ, Дубна. Charmonium. 33 years ago: discovery of J/ ψ , 21 years ago: Matsui & Satz colour screening in deconfined matter → J/ ψ suppression

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А.Б.Курепин – ИЯИ РАН, Москва

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  1. Столкновение релятивистских тяжелых ядер и загадка чармония А.Б.Курепин – ИЯИ РАН, Москва VI Марковские чтения 15 Мая 2008 г. ОИЯИ, Дубна

  2. Charmonium • 33 years ago:discovery of J/ψ, 21 years ago: Matsui & Satz • colour screening in deconfined matter →J/ψ suppression • →possible signature of QGP formation • Experimental and theoretical progress since then → situation is much more complicated • cold nuclear matter / initial state effects • “normal” absorption in cold matter • (anti)shadowing • saturation, color glass condensate • suppression via comovers • feed down from cc, y’ • sequential screening (first: cc, y’, J/y only well above Tc) • regeneration via statistical hadronization or charm coalescence • important for “large” charm yield, i.e. RHIC and LHC

  3. NA50 experimental setup The J/ is detected via its decay into muon pairs Dimuon spectrometer: Centrality detectors: EM calorimeter (1.1< lab<2.3) 2.92 < ylab< 3.92 ZDC calorimeter (lab> 6.3) cos CS < 0.5 Multiplicity detector (1.9<lab<4.2) Pb-Pb 158 GeV/c p – A 400 GeV/c 2000 year Data period Subtargets Number of J/ Target Number of J/ 1995 7 50000 Be 38000 1996 7 190000 Al 48000 1998 1 49000 Cu 45000 2000 1 in vacuum 129000 Ag 41000 W 49000 Pb 69000 J/y suppression is generally considered as one of the most direct signatures of QGP formation (Matsui-Satz 1986)

  4. Fit to the mass spectrum

  5. Light systems and peripheral Pb-Pb collisions:J/ψ is absorpted by nuclear matter . The scaling variable -L (length of nuclear matter crossed by the J/ψ) •  (J/ψ) ~ exp( -abs L) • Central Pb-Pb collisions:the L scaling is broken - anomalous suppression J/ψ suppression from p-A to Pb-Pb collisions J/ψ production has been extensively studied inp-A, S-UandPb-Pbcollisions by the NA38 and NA50 experiments at the CERN SPS Projectile J/y Target J/y normal nuclear absorption curve NA60 : is anomalous suppression present also in lighter In-In nuclear systems ?Scaling variable- L, Npart, ε ?

  6. MWPC’s m ~ 1m Muon Spectrometer Iron wall Hadron absorber Toroidal Magnet Target area m beam Trigger Hodoscopes Dipole field2.5 T ZDC TARGET BOX MUON FILTER Matching in coordinate and in momentum space BEAM BEAMTRACKER VERTEX TELESCOPE IC  not to scale • Origin of muons can be accurately determined • Improved dimuon mass resolution allows studies vs. collision centrality  ZDC NA60 experimental setup High granularity and radiation-hard silicon tracking telescope in the vertex region before the absorber

  7. Comparison of NA50 and NA60results An “anomalous suppression” is presented already in In-In The normal absorption curve is based on NA50 results. Its uncertainty (~ 8%) at 158 GeV is dominated by the (model dependent) extrapolation from the 400 and 450 GeV p-A data. need p-A measurements at 158 GeV

  8. Сomparison J/resultsversus Npart NA50: Npart ftom Et (left) and from Ezdc (right, as in NA60) J/ysuppression inIn-Inis in agreement withPb-Pb S-Uhas different behaviour

  9. Preliminary! ’ suppression(NA38, NA50, NA60) abs=8±1 mb abs~20 mb Small statistics in NA60 In-In for’ (~300) The most peripheral point (Npart~60)– normal nuclearabsorption

  10. Suppression by produced hadrons (“comovers”) The model takes into account nuclear absorption and comovers interaction with σco = 0.65 mb (Capella-Ferreiro) EPJ C42(2005) 419 In-In 158 GeV J/y / NColl nuclear absorption comover + nuclear absorption (E. Ferreiro, private communication) Pb-Pb 158 GeV NA60 In-In 158 GeV

  11. QGP + hadrons + regeneration + in-medium effects The model simultaneously takes into account dissociation and regeneration processes in both QGP and hadron gas (Grandchamp, Rapp, Brown EPJ C43 (2005) 91) In-In 158 GeV fixed thermalization time centrality dependent thermalization time BmmsJ/y/sDY Nuclear Absorption Suppression + Regeneration QGP+hadronic suppression Regeneration Number of participants Pb-Pb 158 GeV centrality dependent thermalization time fixed thermalization time NA60 In-In 158 GeV

  12. Suppression due to a percolation phase transition Model based on percolation (Digal-Fortunato-Satz) Eur.Phys.J.C32 (2004) 547. Prediction: sharp onset (due to the disappearance of the cc meson) at Npart ~ 125 for Pb-Pb and ~ 140 for In-In Pb-Pb 158 GeV NA60 In-In 158 GeV The dashed line includes the smearing due to the resolution

  13. J/transverse momentum distribution Study <pT2> and T dependence on centrality NA60 In-In

  14. J/transverse momentum distribution <pT2> versus L Fitting: <pT2>(L) = <pT2>pp + αgN L <pT2>pp= 1.08 ± 0.02 GeV2/c2 χ2= 0.85  αgN = 0.083 ± 0.002 GeV2/c2fm-1 The observed dependence could simply result from parton initial state multiple scattering

  15. NA50 and NA38 Teff recalculated to 158 GeV vs energy density T(=0) =( 182)2 MeV Tslope = ( 20.16  1.04)  10-3 fm3 Tslope(cent Pb-Pb)=(8.87  2.07) 10-3 fm3 R(slopes)=2.27 +/- 0.54 InNA38 and NA50 TJ/ ψ grows linearly with the energy density and with L. Model dependent recalculation 400 and 200 GeV data to 158 GeV- scaling. For the most central Pb-Pb collisions more flat behaviour could be seen.

  16. J/ψ suppression versus pT. F=(J//DY>4.2 )acc vs pT in 5 ET bins F NA50 Pb-Pb 2000 F Et bins in GeV 1. 5 - 20 2. 20 - 40 3. 40 - 70 4. 70 - 100 5. >100 pT

  17. Suppression vs pT for p-A, S-U and Pb-Pb Rcp p-A S-U ~Aα Cronin effect- enhancement at pT>2 GeV/c Pb-Pb 2000 Rcp Et bins GeV 5 - 40 40 - 80 80 – 125

  18. 1.5-5% 5-10% 10-16% 0-1.5% RCP 23-33% 16-23% 33-47% pT (GeV/c) Rcp vs pT. NA60 In-In Rcp = (J/ψi(pT)/Ncolli)/(J/ψ1(pT)/Ncoll1) The ratios to the peripheral i=1 (47-57%)bin. Large suppression at low pT, growing with centrality- as in RAA NA60 and in Rcp NA50.

  19. J/ in PHENIX J/  e+e– identified in RICH and EMCal • |y| < 0.35 • Pe > 0.2 GeV/c •  =  J/μ+μ– identified in 2 fwd spectrometers South : • -2.2 < y < -1.2 North : • 1.2 < y < 2.4 • P > 2 GeV/c •  = 2  Event centrality and vertex given by BBC in 3<||<3.9 (+ZDC) Centrality is calculated to Npart (Ncoll) using Glauber model

  20. Yan, Zhuang, Xu nucl-th/0608010 All models for y=0 nucl-ex/0611020 nucl-ex/0611020 J/,’,c Satz Capella Rapp Suppression RAA vs Npart at RHIC. PHENIX Au-Au data Models for mid-rapidity Au-Au data Without regeneration With regeneration

  21. J/ψ suppression (SPS and RHIC) J/ψ yield vs Npart, normalized on Ncoll. Unexpected good scaling. Coherent interpretation- problem for theory. Work start - : Karsch, Kharzeev and Satz., PRL637(2006)75

  22. arXiv:0801.0220 [nucl-ex] J/ψ suppression RAA vs pT at PHENIX. Au-Au Cu-Cu nucl-ex/0611020 For low pT suppression grows with centrality.

  23. Comparison SPS (NA60) and RHIC (PHENIX) data The same suppression at low pT. Larger values of <pT2> at RHIC

  24. Suppression RAA in Au-Au (PHENIX) vs pT. P J/ψ up to only 5 GeV Central events The same RAA for 0,  at all pT and J/ (up to 4 GeV/c). RAA for  is higher. RAA for direct  <1 for high pT.

  25. J/ψ suppression RAA at RHIC. PHENIX and STAR Cu-Cu data • Data consistent with no suppression at high pT: RAA(pT > 5 GeV/c) = 0.9 ± 0.2 • At low-pT RAA: 0.5—0.6 (PHENIX) • RAA increase from low pT to high pT • Most models expect a decrease RAA at high pT: X. Zhao and R. Rapp, hep-ph/07122407 H. Liu, K. Rajagopal and U.A. Wiedemann, PRL 98, 182301(2007) and hep-ph/0607062 •  But some models predict an increase RAA • at high pT: • K.Karch and R.Petronzio, 193(1987105; • J.P.Blaizot and J.Y.Ollitrault, PRL (1987)499

  26. Conclusions • At SPS energiesthe J/y shows an anomalous suppression discovered in Pb-Pb and existing already in In-In • None of the available models properly describes the observed suppression pattern simultaneously in Pb-Pb and In-In • The  shows an anomalous suppression for S-U, In-In • and Pb-Pb • At RHIC energies the J/suppression is of the same order as at SPS • None of the theoretical model could describe all the data • The transverse momentum dependence of J/ψ suppression shows • suppression mainly ay low pT, growing with centrality • Need information at high pT.

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