J/  production in Cu+Cu and Au+Au collisions at √s = 200 GeV measured by PHENIX at RHIC Andry Rakotozafindrabe LLR – École Polytechnique (France) PHENIX Collaboration SQM 2006

26/03/2006Andry Rakotozafindrabe – LLR2 Physics motivation  The J/  is a promising hard probe to study the hot and dense matter created in relativistic heavy ion collisions : Produced in the early stages of the collision only and interacts with the surrounding medium Produced in the early stages of the collision only and interacts with the surrounding medium  Changes to the J/  yield can be due to competing effects : Suppression by color screening in a deconfined medium Suppression by color screening in a deconfined medium Enhancement at RHIC energy due to recombination of uncorrelated cc pairs Enhancement at RHIC energy due to recombination of uncorrelated cc pairs Cold nuclear effects ( shadowing, nuclear absorption ) Cold nuclear effects ( shadowing, nuclear absorption )  p+p measurement is used as a reference, while d+Au measurement is used to evaluate the cold nuclear effects.  At lower energy, NA50 (CERN) experiment measured an anomalous J/  suppression in Pb+Pb collisions, in excess of the normal suppression expected from the nuclear absorption. (NA50 Collaboration, Phys. Lett. B477 (2000) 28)

26/03/2006Andry Rakotozafindrabe – LLR3 PHENIX detector J/  µ + µ – 1.2< |y| < 2.2 P µ > 2 GeV/c  = 2  Tracking, momentum measurement with cathode strip chambers µ ID with penetration depth / momentum match J/   e + e – |y| < 0.35 P e > 0.2 GeV/c  =  Tracking, momentum measurement with drift chambers, pixel pad chambers e ID with EmCAL + RICH Centrality measurement, vertex position Beam-beam counters (charged particle production) Zero-degree calorimeters (spectator neutrons)

26/03/2006Andry Rakotozafindrabe – LLR4 σ abs =1 mb RHIC : beyond cold nuclear effects ?  Available d+Au data : Weak shadowing (modification of gluon distribution) and weak nuclear absorption () Weak shadowing (modification of gluon distribution) and weak nuclear absorption (σ abs ~ 1mb favored)  Au+Au data : even compared to the « worst » σ abs ~ 3mb case Factor 2 of suppression Au+Au bin Factor 2 of suppression beyond cold effects in the most central Au+Au bin R dA Phys. Rev. Lett 96, (2006) 1 mb 3 mb rapidity σ abs =3 mb Suppression Factor ~ 2 Number of participants

26/03/2006Andry Rakotozafindrabe – LLR5 RHIC vs SPS (I) : raw comparison  SPS : √s ~ 17 GeV i.e. a factor 10 below RHIC √s ~ 17 GeV i.e. a factor 10 below RHIC Cold effect = σ abs = 4.18 ± 0.35 mb Cold effect = normal nuclear absorption σ abs = 4.18 ± 0.35 mb Maximum ε ~ 3 GeV/fm 3 (τ 0 = 1) Maximum ε ~ 3 GeV/fm 3 (τ 0 = 1)  Compare to RHIC : Cold effect = σ abs ~ 1mb (Vogt, nucl- th/ ) Cold effect = shadowing + nuclear absorption σ abs ~ 1mb (Vogt, nucl- th/ ) Maximum ε ~ 5 GeV/fm 3 (τ 0 = 1), higher than at SPS, but still, the ! Maximum ε ~ 5 GeV/fm 3 (τ 0 = 1), higher than at SPS, but still, the same pattern of J/  suppression ! SPS normalized to NA51 p+p value (NA60 preliminary points from Arnaldi, QM05). NA50 Pb+Pb NA60 In+In PHENIX Au+Au PHENIX Cu+Cu PHENIX cold effect NA50 cold effect PHENIX : |y|~1.7

26/03/2006Andry Rakotozafindrabe – LLR6 RHIC vs SPS (II) : extrapolating suppression models  Suppression models in agreement with NA50 data overestimate the suppression when extrapolated at RHIC energies : quite striking for mid and most central Au+Au bins quite striking for mid and most central Au+Au bins already the case for Cu+Cu most central bins ? already the case for Cu+Cu most central bins ? (Hadronic?) co-mover scattering Direct suppression in a hot medium : Cu+CuAu+Au

26/03/2006Andry Rakotozafindrabe – LLR7 Some recombination effects ?  Adding some regeneration that partially compensates the suppression : there is a better agreement between the model and the data. Direct suppression in a hot medium : Cu+CuAu+Au Regeneration : Cu+CuAu+Au Total : Cu+CuAu+Au Grandchamp et al. hep-ph/

26/03/2006Andry Rakotozafindrabe – LLR8 Recombination predictions for vs N coll  Recombination ( Thews et al., nucl-th/ ) predicts a narrower p T distribution with an increasing centrality, thus leading to a lower  Within the large error bars : seems to be consistent with a flat dependence seems to be consistent with a flat dependence falls data falls between the two hypothesis  partial recombination ? p+p, d+Au, Cu+Cu, Au+Au No recombination With recombination No recombination With recombination Open markers : |y|<0.35 Solid markers : |y|~1.7

26/03/2006Andry Rakotozafindrabe – LLR9 Recombination predictions vs rapidity  Recombination ( Thews et al., nucl-th/ ) predicts a narrower rapidity distribution with an increasing N part.  Going from p+p to the most central Au+Au : no significant change seen in the shape of the rapidity distribution. No recombination All recombination

26/03/2006Andry Rakotozafindrabe – LLR10 Summary PHENIX preliminary results on J/  dileptons at forward and mid-rapidity in Cu+Cu and Au+Au :  Suppression pattern Beyond cold nuclear effects, at least factor 2 of suppression in most central Au+Au events Beyond cold nuclear effects, at least factor 2 of suppression in most central Au+Au events Similar to SPS suppression, despite a higher energy density reached Similar to SPS suppression, despite a higher energy density reached Overestimated by models in agreement with NA50 data and extrapolated at RHIC energy Overestimated by models in agreement with NA50 data and extrapolated at RHIC energy  Understandable as recombinations that partially compensate the J/  suppression ? Still open question (test vs dependance and rapidity distribution) Still open question (test vs dependance and rapidity distribution)  Alternate explanations ? Direct J/  is not melting at present energy densities ? Only the higher mass resonances  ’ and χ c ? (recent lattice QCD results) Direct J/  is not melting at present energy densities ? Only the higher mass resonances  ’ and χ c ? (recent lattice QCD results) J/  transport (with high p T J/  escaping QGP region) + QGP suppression ? J/  transport (with high p T J/  escaping QGP region) + QGP suppression ?  Need to improve knowledge on cold nuclear effects at RHIC

26/03/2006Andry Rakotozafindrabe – LLR11 Back-up

26/03/2006Andry Rakotozafindrabe – LLR12 RHIC vs SPS  Plotted « à la SPS » way i.e. normalize the J/  production with the cold nuclear effects : nuclear absorption with σ abs = 4.18 ± 0.35 mb at SPS nuclear absorption with σ abs = 4.18 ± 0.35 mb at SPS Shadowing + nuclear absorption with σ abs ~ 1 mb at RHIC (Vogt, nucl-th/ ) Shadowing + nuclear absorption with σ abs ~ 1 mb at RHIC (Vogt, nucl-th/ ) (NA60 preliminary points from Arnaldi, QM05). NA50 Pb+Pb NA60 In+In PHENIX Au+Au PHENIX Cu+Cu PHENIX : |y|~1.7

26/03/2006Andry Rakotozafindrabe – LLR13 SPS vs RHIC  RHIC : √s = 200 GeV √s = 200 GeV R AA i.e. (J/  in A+A) / (Ncoll * J/  in p+p) R AA i.e. (J/  in A+A) / (Ncoll * J/  in p+p) « expected » = nuclear absorption (σ ~ 1 à 3 mb ) + shadowing « expected » = nuclear absorption (σ ~ 1 à 3 mb ) + shadowing |y| = [0,0.35] or [1.2,2.2] |y| = [0,0.35] or [1.2,2.2]  SPS : √s ~ 17 GeV √s ~ 17 GeV Measured/expected Measured/expected measured = J/  / D.Y measured = J/  / D.Y expected = normal nuclear absorption expected = normal nuclear absorption σ = 4.18 ± 0.35 mb NA50: |y*| = [0,1] NA50: |y*| = [0,1] (Arnaldi, QM05) |y|<0.35 |y|~1.7 + private communications d+Au Cu+Cu Au+Au

26/03/2006Andry Rakotozafindrabe – LLR14 Invariant yield vs p T  we fit the p T spectrum using to extract Cu+Cu (|y|  [1.2,2.2])Au+Au (|y|  [1.2,2.2])

26/03/2006Andry Rakotozafindrabe – LLR15 Computing the J/  yield : number of ‘s reconstructed : probability for a thrown and embeded into real data to be found (considering reconstruction and trigger efficiency) : total number of events : BBC trigger efficiency for events with a : BBC trigger efficiency for minimum bias events Invariant yield : For Au+Au or Cu+Cu collision : ~ i : i-th bin (centrality for e.g.)

26/03/2006Andry Rakotozafindrabe – LLR16 –1.95 < y < –1.70 Signal extraction in Cu+Cu  Cuts : Dimuons cuts 2.6 < mass < 3.6 GeV/c² 2.6 < mass < 3.6 GeV/c² 1.2 < |rapidity| < < |rapidity| < 2.2 Track quality cuts …  Combinatoric background from uncorrelated dimuons : N bgd = 2√(N ++. N – – ) N bgd = 2√(N ++. N – – )  Signal = number of counts within the J/  invariant mass region  (2.6 – 3.6 GeV/c²) after subtracting N bgd to the distribution of the opposite sign dimuons.  Systematic errors : ~10% from varying fits of the background subtracted signal. Also account for the physical background that can be included into the previous counting.

26/03/2006Andry Rakotozafindrabe – LLR17 Getting acc*eff correction factors in Cu+Cu  Using Monte Carlo J/  generated by PYTHIA over 4π  embed the J/  within muon arm acceptance into real minimum bias Cu+Cu data  Apply to them the same triggers and signal extraction method as the ones applied to the data  Acc.eff(i) is the probability that a J/  thrown by PYTHIA in a given bin i to survive the whole process followed by the data Acc*eff vs rapidity (statistical errors only) Systematic errors : 5% from track/pair cuts and uncertainities in p T, y and z-vertex input distribution 8% from run to run variation (mainly due to the varying number of dead channels in MuTr). Acc*eff vs p T (statistical errors only)Acc*eff vs centrality (statistical errors only)

26/03/2006Andry Rakotozafindrabe – LLR18 J/  production in p+p Total cross section in p+p  = 2.61  0.20  0.26 µb = 2.51 ± 0.21 (GeV/c) 2 Phys. Rev. Lett. 96, y

26/03/2006Andry Rakotozafindrabe – LLR19 y < -1.2 : large x Au ~ y ~ 0 : intermediate x Au ~ y > 1.2 : low x Au ~ xdxd x Au J/  North y > 0 xdxd x Au J/  South y < 0 rapidity y gluons in Pb / gluons in p x Shadowing Anti Shadowing Nucl. Phys. A696 (2001) J/  production in d+Au 0 mb 3 mb Low x 2 ~ (shadowing region)

26/03/2006Andry Rakotozafindrabe – LLR20  Small centrality dependence  Models with absorption + shadowing : shadowing EKS98 shadowing EKS98 σ abs = 0 to 3 mb σ abs = 0 to 3 mb  σ abs = 1 mb good agreement  σ abs = 3 mb is an upper limit  weak shadowing and weak nuclear absorption J/  production in d+Au vs centrality

26/03/2006Andry Rakotozafindrabe – LLR21 J/  and the colour screening in QGP  Temperature of dissociation T d for χ c and  ’: T d ~ T c for χ c and  ’: T d ~ T c for J/  : T d ~ 1.5 to 2 T c for J/  : T d ~ 1.5 to 2 T c  Sequential dissociation vs energy density ~ ~ 60% direct production J/  ~ 30% via χ c  J/  + x ~ 10% via  ’  J/  + x ’’J/  χcχc  Production g+g fusion dominant at RHIC energy g+g fusion dominant at RHIC energy  Energy density vs the max. √s for SPS, RHIC and LHC cf. [1] Satz, hep-ph/ [2] Karsch et al. hep-ph/ Figure from [1]

26/03/2006Andry Rakotozafindrabe – LLR22 Collision geometry and centrality (eg : Cu+Cu) For a given b, Glauber model (Woods-Saxon function) predicts: ● N part (No. participants) ● N coll (No. binary collisions) 10 fm b 0 fm 0 N part N coll 198 Spectators (neutrons) E ZDC Participants (charged particles) Q BBC BBC charge N+S distribution for min.bias Cu+Cu √s = 200 GeV data 80-88% 70-80% etc Monte-Carlo Glauber model Probability for a given Npart Each participant contributes to a Negative Binomial distribution of hits Fit BBC charge distribution

26/03/2006Andry Rakotozafindrabe – LLR23 YearIons  s [GeV] ∫Ldt Number of J/  Data Size Run 12000Au+Au130 1  b TB Run Au+Au  b TB p+p pb TB Run d+Au nb TB p+p pb TB Run Au+Au  b -1 ~ TB  b expected10 TB p+p nb -1 Run Cu+Cu 2003 nb -1 ~ TB nb -1 ~ TB  b -1 1 TB p+p pb -1 > 6500 expected 262 TB Run 1 to Run 5 capsule history and J/  in PHENIX

26/03/2006Andry Rakotozafindrabe – LLR24 Cu+Cu 200 GeV data taking: triggers and level2 filtering Volumeof data 50 Tb 2.5 Tb 173 Tb 500 Mb Minimum Bias trigger: BBC Level1 trigger: MuID Deep-Deep Reconstruction Level2 filtering: MuTr + MuID New ! fast online reconstruction of 1D road in MuID di-road accepted if last MuID gap reached (with a minimum number of hit gaps) reconstruction of 2D road in MuID used as seed for MuTr track finding rough track momentum estimate  invariant mass cut for tracks pairs at 2 GeV/c²

26/03/2006Andry Rakotozafindrabe – LLR25 J/  as a probe of the produced medium (I)  Hard probe Large charme quark mass (m J/  ~3.1 GeV/c²)  J/  produced at early stages of the collision Large charme quark mass (m J/  ~3.1 GeV/c²)  J/  produced at early stages of the collision Size r J/  ~0.2 fm < typical hadronique size (~1 fm) Size r J/  ~0.2 fm < typical hadronique size (~1 fm) Recent lattice QCD result : melting temperature in a deconfined medium is Recent lattice QCD result : melting temperature in a deconfined medium is T ~ 1.5 à 2 T C  Production g+g fusion g+g fusion p+p  reference for p+A or A+A r ratios (p+A)/(p+p) or (A+A)/(p+p)  Suppression or enhancement of the J/  yield : Due to nuclear matter or to deconfined medium Due to nuclear matter or to deconfined medium ? PDF ~ ~60% direct production J/  ~30% via χ c  J/  + x ~30% via χ c  J/  + x ~10% via  ’  J/  + x ~10% via  ’  J/  + x

26/03/2006Andry Rakotozafindrabe – LLR26 J/  as a probe of the produced medium (II)  Initial state effect CGC, shadowing CGC, shadowing Cronin effect : multiple elastic scattering  p T broadening Cronin effect : multiple elastic scattering  p T broadening Evaluated via p+A ou d+A   Final state effect Nuclear ( hadronic ) absorption QGP ? suppression : « colour screening » or enhancement : recombinaison From 10 to 20 cc in central Au+Au at RHIC Accessible via A+A PDF J/J/ L Projectile Cible V(r) r ’’J/  χcχc

26/03/2006Andry Rakotozafindrabe – LLR27 Background sources  Physical background: correleted dimuons Drell-Yan: Drell-Yan: Open charm: Open charm: D, D  µ ± + …  Combinatoric background: uncorrelated dimuons  , K   µ  + … (decay before the absorber)  , K   µ  + … (decay before the absorber)

26/03/2006Andry Rakotozafindrabe – LLR28 Energy density  Longitudinally expanding plasma : dE T /dη measurement at mid-rapidity by PHENIX EMCal dE T /dη measurement at mid-rapidity by PHENIX EMCal Which τ 0 ? Which τ 0 ? R2R2 00 ~ 1 fm/c  cross ~ 0.13 fm/c  secondaries formation ~ 0.35 fm/c  therm ~ fm/c

26/03/2006Andry Rakotozafindrabe – LLR29 Commonly used variables  Transverse : perpendicular to the beam direction  Transverse momentum : p T = sqrt( p 2 x + p 2 y )  Rapidity : y = 1/2 ln (E+p z )/(E-p z )  Pseudorapidity : η = 1/2 ln (p+p z )/(p-p z )  Invariant mass of a pair : M 2 inv = (E 1 +E 2 ) 2 - (p 1 +p 2 ) 2