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Review of Electromagnetic Probes O. Drapier LLR-École Polytechnique, France

Review of Electromagnetic Probes O. Drapier LLR-École Polytechnique, France. ?. Direct Photons. Single leptons, Dileptons. Electromagnetic probes ?. g. t. p,n. l ±. B. B. p ,k. kinetic freeze-out. chemical freeze-out. hadronization. hadrons. chiral symmetry ? thermal equilib. ?

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Review of Electromagnetic Probes O. Drapier LLR-École Polytechnique, France

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  1. Review of Electromagnetic ProbesO. DrapierLLR-École Polytechnique, France ?

  2. Direct Photons Single leptons, Dileptons Electromagnetic probes ? g t p,n l± B B p,k kinetic freeze-out chemical freeze-out hadronization hadrons chiral symmetry ? thermal equilib. ? chemical equilib. ? deconfinement ? mixed phase ? plasma partons thermalization z

  3. Compare to NLO pQCD • L.E.Gordon and W. Vogelsang • Phys. Rev. D48, 3136 (1993) • excess above pQCD Photons ! (S.Bathe, 6b) See next talk by C. Gale Compare to thermal model • D. d’Enterria, D. Perresounko • nucl-th/0503054 2+1 hydro T0ave=360 MeV(T0max=570 MeV) t0=0.15 fm/c • data above thermal at high pT Compare to thermal + pQCD • data consistent with thermal + pQCD

  4. p+Cu, 12 GeV C+C, 2 AGeV R.Muto, Kek-PS-E325,6a R.Holtzmann, Hades, 6a within acceptance SPS, 158 AGeV S.Damjanovic, NA60, 6a D. Miskowiec, CERES Low mass dileptons • From low energies … See next talk by C. Gale • To SPS …

  5. Outline • Charm and Charmonium

  6. Review of Electromagnetic ProbesO. DrapierLLR-École Polytechnique, France Not exactly a

  7. Let’s start with NA50 J/y • Precise re-analysis of p-A data • s scaling, kinematical domain, • neutron halo, … • sabs(J/y) = 4.18 ± 0.35 mb • sabs(y’) = 7.6 ± 1.1 mb • Why sabs ? Why not Aa ? L. Ramello, NA50

  8. Aa = straight line here e –r <L>sabs = straight line here C. Lourenço Student’s session Calculations by Ruben Shahoyan a vs sabs • Not equivalent ! • Depends on which nuclei you take • + r < L > or < rL > are only approximations

  9. Doesn’t seem to play a role at NA50 Xf, otherwise would be seen on the  • Energy loss of initial gluon: • Depends on Xf • Less important at RHIC P. Cortese, NA50, 5b B d() / dycm at ycm = 0 P. Cortese, NA50, 5b M. Leitch, E866, Eur.Phys.J.A (2004) 19, S01, 129 Curve from Kopeliovich et al., Nucl. Phys. A696 (2001) 669 sabs • e – <rL> sabs = intuitive if J/y disappearance in an absorbing medium. May depend on s !! • Can be even much more complex that that ! • Combination of energy loss of the initial parton + J/y « absorption » in nuclear matter

  10. Not reproduced by models • Even if they fit NA50 data Satz, Digal, Fortunato Rapp, Grandchamp, Brown Capella, Ferreiro PLATEAU ??? NA60 • In+In @ 158 A.GeV • E. Scomparin, R. Arnaldi, 6a • Anomalous suppression ! • Even if they fit NA50 data • Onset in the range 80 < Npart < 100 R. Arnaldi, NA60

  11. very preliminary What is the relevant variable ? • There is NO unique universal variable • Depends on what you want to show • e.g. : anomalous suppression is NOT an absorption by nuclear matter • More tricky if you need to compare different s !!! • e.g. e allows comparisons • L or Ldon’t • pure geometry R. Arnaldi, NA60

  12. etc… 20-25 % 15-20 % 10-15 % NA60 5-10 % 90-95 % 0-5 % Number of Participants PHENIX What is the relevant variable ? • So, in principle we should: • Calculate all the effects that might change with s • Subtract them or plot them on top of the data for comparison • Plot the result vs the variable corresponding to the effect you want to test/rule out • But these variables are model dependent • & experiment dependent = nobody else than the experiment can calulate these quantities L. Ramello, NA50

  13. SPS -> RHIC • Charm and charmonium cross-sections • Opens the door for cc recombination into J/y • N(cc) up to 40 in a central Au+Au collision ! • R.L. Thews & R.L. Mangano, nucl-th/0505055 J. Dunlop - -

  14. Open charm measurements @ SPS ? • The « intermediate mass dilepton » puzzle @ SPS: • Is there an enhancement of charm, or charm-like contribution ? • The answer is : NO, the excess exists, but it’s PROMPT • For now, not enough precision to measure charm cross-section … Dimuon weighted offsets in NA60 R. Shahoyan, 5b

  15. Open charm @ RHIC • Open charm is measured by • Single « non-photonic » electrons in PHENIX and STAR • Direct D->kp in STAR (see H. Zhang, 5c) • Limited PT domain • « binary scaling » = as Ncoll • MORE PRECISION NEEDED ! S. Butsyk, 5a J. Dunlop PHENIX, S.S. Adler, et al., PRL 94 082301

  16. Djordjevic et al, nucl-th/0507019 Charm @ RHIC : high PT suppression • Nuclear modification factor (S. Butsyk, 5a, J. Bielcik, 5c) • For more details, see J. Bielcik this afternoon • High PT suppression does not change charm yields J. Dunlop See talk by X. Dong

  17. Charm @ RHIC : Flow ! • Charmed particles have a large V2 at RHIC ! • Charm « quenching » and V2 were not expected • Higher quark mass -> less gluon radiation (’’dead cone effect’’) • e.g. : Y. L. Dokshitzer & D.E. Kharzeev, Phys.Lett.B519(2001)199-206 • Hard process -> no flow • Influence of light quark flow ? See talk by X. Dong Theory:Greco, Ko, Rapp: PLB 595 (2004) 202 STAR, F. Laue, 5a S. Butsyk, 5a

  18. X2 X1 J/ South y < 0 X1 X2 J/ North y > 0 d Pb / p Au Anti Shadowing Shadowing X2 X1 J/ Central y < 0 X rapidity y Cold nuclear effects • Heavy flavor = probe for « cold » nuclear effects • Parton distribution functions are modified in nuclei • e.g. in d-Au collisions : Anti-shadowing Nothing ? Shadowing

  19. X Cold nuclear effects • PHENIX d+Au @ 200 GeV (nucl-ex/050732, W. Xie, 5c) • (anti)shadowing clearly visible • sabs seems lower than @ SPS • ~1 mb, 3mb overestimated • Dependence with centrality • For Au+Au = mirror distribution

  20. J/ymm muon arm 1.2 < |y| < 2.2 J/yee Central arm -0.35 < y < 0.35 AuAu mm 200 GeV/c CuCu mm 200 GeV/c AuAu ee 200 GeV/c CuCu ee 200 GeV/c dAu mm 200 GeV/c CuCu mm 62 GeV/c Now let’s move to PHENIX J/y • J/y in STAR ! See H. Zhang, 5c this afternoon • J/y in PHENIX : H. Büsching, H. Perreira Da Costa, 6b

  21. Suppression = 35 to 40 % wrt to sabs = 3mb (overestimated) • ~ equivalent to NA50 • Need better reference !!! J/y in PHENIX • Tempting to plot NA50 points on top of this, isn’t it ? • Well … interesting but … • Meaning of Npart when s * 10 ? • NA50 points normalized to p+p • What if sabs different ? • Shadowing ? • Better : compare to absorption + shadowing H.Pereira Da Costa, 6b

  22. Satz Rapp-Grandchamp Capella-Ferreiro J/y in PHENIX • Models: • The models « which fit NA50 data » overestimate the suppression • Regeneration needed ??? • MAYBE, but • These models DO NOT fit NA60 ! • Comovers severely underestimate suppression in In+In • Rapp & Grandchamp doesn’t saturate as seen in the data • Only Satz fits the end of the plateau with Xc suppression only. • NO direct J/y suppression ? • Would be consistent with recent lattice QCD calculations See talk by M. Nardi c R. Arnaldi, NA60 J/y ?

  23. - c-c recombinations ? • It seems that these models can reproduce the data, when they turn on the recombination process • Consequences on the other variables ?

  24. Rapidity distributions • Rapidity distribution of recombined J/y is supposed to be peaked at y=0 (e.g. R.L. Thews & al., nucl-th/0505055) • True IF charm distribution ~ J/y in p+p ! • But Au+Au charm rapidity distributions might be very flat ! mainly « off-diagonal » p+p data pQCD, adjust <kT2> « diagonal » H.Pereira Da Costa, 6b

  25. PHENIX PRELIMINARY Rapidity distributions • Comparing charm cross-sections in PHENIX central and muons arms: • Au+Au charm rapidity distributions might be very flat in Au+Au ! • Just an indication, because of the limited PT domain • If flat distribution of charm production : • Lowers charm density -> less regeneration • Rapidity distribution of regenerated less peaked at 0 See talk by Y. Kwon, 5c this afternoon !

  26. Without With H.Pereira Da Costa, 6b PT distributions ? • PT distribution of recombined J/y is very narrow (R.L. Thews & al., nucl-th/0505055) • Leads to a drastic reduction of <PT2> in case of recombination • BUT <PT2> calculated from p+p and d+Au (via <kT2>) • Large error bars • Need for more p (or d) + A data !! (e.g. p+p to d+Au in e±) mainly « off-diagonal » « diagonal »

  27. PT distributions ? Back to SPS • NA50 suppression at low PT … • Compatible with high PT charm pairs escaping the hot region before forming the J/y • The same mechanism at RHIC would lead to an increase of <PT2> • Very different from regeneration Low PT pairs cannot form a J/y High PT pairs can escape At RHIC, <PT2> much higher than at sps, but plasma longer lived. What is the net result for J/y ? F. Karsch & R. Petronzio M.C. Chu & T. Matsui J.P. Blaizot & J.Y. Ollitrault

  28. solid: STAR open: PHENIX PRL91(03) Is there a J/y flow ? Regenerated J/y should lie on this curve V2/2 vs PT/2 ! • Charm flows  recombined J/y must flow ! • Directly produced J/y shouldn’t flow but suppression might be stronger out of reaction plane (as for Jets) … • Can simulate some flow for surviving J/y ? • Comovers should be more active in-plane •  those J/y which survive interactions with comovers would have a negative V2 ????

  29. Conclusion (1) • A LOT OF BEAUTIFUL NEW DATA ! • SPS : • CERES excess confirmed by NA60 • Intermediate mass excess in dimuon spectra confirmed by NA60 • IT IS NOT OPEN CHARM, it’s prompt • NA50 has re-analyzed p+A reference • Anomalous J/y suppression confirmed by NA60 in In+In • RHIC • Direct photons at low PT from PHENIX, consistent with thermal emission • Open charm is suppressed at high PT • Significant flow observed for open charm • J/y suppression is seen by PHENIX, not stronger than in NA50 • Models without recombination of charm quarks are unable to account for the data

  30. Conclusion (2) • WE MUST TAKE SOME TIME, Interpreting J/y suppression is a tricky thing • Reproduce ALL SPS data • Extrapolate to RHIC • Shadowing • Normal absorption • Measured flow • Measured Y and PT distributions • THEN ONLY compare to RHIC data • We need GOOD REFERENCES ! • p+A @ SPS (NA50, NA60 to be analyzed) • p+A or d+A at RHIC • We need good statistics + several systems !!!!

  31. Conclusion (3) Only a joke ! NA38, QM’91

  32. Thank You ! Special thanks to: F. Fleuret for his help for preparing this talk, L. Kluberg, C. Lourenço, D. D’Enterria, R. Granier de Cassagnac and many others, for usefull discussions

  33. Backup Slides

  34. Kharzeev, Nardi & Satz D.Kharzeev, M.Nardi and H.Satz, Phys. Lett. B405 (1997) 14

  35. Heavy flavor production • ’’Onia’’ production • Leading order at low x = ’’gluon fusion’’ • Sensitive to: J/y or  • Initial state • Parton distribution functions • pT broadening • Parton energy loss in the initial state ? • Polarization ? • Final state • Parton energy loss in the hot & dense medium ? • Thermal enhancement ? • Flow ? + feed-down (e.g. B or c-> J/y)

  36. Heavy flavor production • Open charm (or beauty) production • Leading order at low x = ’’gluon fusion’’ • Sensitive to: • Initial state • Parton distribution functions • pT broadening • Parton energy loss in the initial state ? • Polarization ? • Final state • Parton energy loss in the hot & dense medium ? • Thermal enhancement ? • Flow ?

  37. d-Au (√s = 200 GeV) • d-Au: binary scaling also holds for different centralities PHENIX PRELIMINARY PHENIX PRELIMINARY

  38. Au-Au (√s = 62.4 GeV) • Open charm in Au-Au @ 62.4 GeV, as compared to ISR p-p data at the same incident energy • Also compatible with <Ncoll> scaling PHENIX PRELIMINARY

  39. Recent evolutions in f µµ B.R. 1999: only average of values of f photoproduction 2000 BRµµ included in the overall PDG fit new imprecise measurement of ee->µµ : increase of BRµµ 2002 better ee->µµ measurement, confirming universality principle 1999-2000-2002 : 2.5 – 3.7 – 2.87 2004: BRfµµ = (2.85±0.19) 10-4 ; BRfee = (2.98±0.04) 10-4 • Year PDG average PDG fit • 2.5 - ee->µµ CS is not used in the fit • 2.5 3.7 Achasov 99C (3.30) appears • 2.5 2.87 Achasov 01G (2.87) appears • 2004 2.5 2.85 No new data on this mode

  40. Phi puzzle

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