А.Б.Курепин – ИЯИ РАН, Москва Столкновение релятивистских тяжелых ядер и загадка чармония 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 - → 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  c,  ’ – sequential screening (first:  c,  ’, J/  only well above T c ) – regeneration via statistical hadronization or charm coalescence ● important for “large” charm yield, i.e. RHIC and LHC

NA50 experimental setup The J/  is detected via its decay into muon pairs Dimuon spectrometer: Centrality detectors : EM calorimeter (1.1<  lab <2.3) )  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/  Be Al Cu in vacuum Ag W Pb J/  suppression is generally considered as one of the most direct signatures of QGP formation (Matsui-Satz 1986)

Fit to the mass spectrum

J/ψ suppression from p-A to Pb-Pb collisions Projectile Target J/J/ J/ψ production has been extensively studied in p-A, S-U and Pb-Pb collisions by the NA38 and NA50 experiments at the CERN SPS J/  normal nuclear absorption curve 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 NA60 : is anomalous suppression present also in lighter In-In nuclear systems ? Scaling variable- L, Npart, ε ?

NA60 experimental setup MUON FILTER BEAM TRACKER TARGET BOX VERTEX TELESCOPE Dipole field 2.5 T BEAM IC not to scale Origin of muons can be accurately determined Improved dimuon mass resolution  Matching in coordinate and in momentum space ZDC  allows studies vs. collision centrality beam ~ 1m Muon Spectrometer MWPC’s Trigger Hodoscopes Toroidal Magnet Iron wall Hadron absorber ZDC Target area   High granularity and radiation-hard silicon tracking telescope in the vertex region before the absorber

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 Comparison of NA50 and NA60 results An “anomalous suppression” is presented already in In-In

Сomparison J/  results versus N part NA50: Npart ftom Et (left) and from Ezdc (right, as in NA60) J/  suppression in In-In is in agreement with Pb-Pb S-U has different behaviour

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

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

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

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

J/  transverse momentum distribution Study and T dependence on centrality NA60 In-In

J/  transverse momentum distribution versus L Fitting : (L) = pp + α gN L pp = 1.08 ± 0.02 GeV 2 /c 2 χ 2 = 0.85  α gN = ± 0.002 GeV 2 /c 2 fm -1 The observed dependence could simply result from parton initial state multiple scattering

NA50 and NA38 Teff recalculated to 158 GeV vs energy density In NA38 and NA50 T J/ 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. T(  =0) =( 182)  2 MeV Tslope = (  1.04)  fm 3 Tslope(cent Pb-Pb)=(8.87  2.07) fm 3 R(slopes)=2.27 +/- 0.54

J/ψ suppression versus p T. F=(J/  DY>4.2  acc vs p T in 5 E T bins NA50 Pb-Pb 2000 Et bins in GeV >100 F pT pT F

Suppression vs p T for p-A, S-U and Pb-Pb S-U Pb-Pb 2000 Et bins GeV – 125 p-A Cronin effect- enhancement at p T >2 GeV/c Rcp  ~A α

p T (GeV/c) R CP 0-1.5% 1.5-5%5-10%10-16% 16-23% 23-33% 33-47% NA60 In-In The ratios to the peripheral i=1 (47-57%) bin. Large suppression at low p T, growing with centrality- as in R AA NA60 and in R cp NA50. R cp vs p T. R cp = (J/ψ i (p T )/N coll i )/(J/ψ 1 (p T )/N coll 1 )

J/  in PHENIX J/   e + e – identified in RICH and EMCal –|y| < 0.35 –P e > 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

Satz Rap p Capella J/ ,  ’,  c All models for y=0 nucl-ex/ Yan, Zhuang, Xu nucl-th/ PHENIX Au-Au data Without regenerationWith regeneration Models for mid-rapidity Au-Au data Suppression R AA vs N part at RHIC.

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

For low p T suppression grows with centrality. J/ψ suppression R AA vs p T at PHENIX. nucl-ex/ Au-Au arXiv: [nucl-ex] Cu-Cu

Comparison SPS (NA60) and RHIC (PHENIX) data The same suppression at low p T. Larger values of at RHIC

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

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

At SPS energies the J/  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 p T, growing with centrality Need information at high p T. Conclusions