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Overview of Experimental results from RHIC

Overview of Experimental results from RHIC. Y. Akiba (RIKEN Nishina Center) ATHIC08 Tsukuba October 13, 2008. QCD Phase Transition. The colliding nuclei at RHIC energies would melt from protons and neutrons into a collection of quarks and gluons

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Overview of Experimental results from RHIC

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  1. Overview of Experimental results from RHIC Y. Akiba (RIKEN Nishina Center) ATHIC08 Tsukuba October 13, 2008

  2. QCD Phase Transition • The colliding nuclei at RHIC energies would melt from protons and neutrons into a collection of quarks and gluons • A QCD phase transition that the universe last went through ~1ms after the Big Bang Tc ~ 170 MeV; e ~ 1 GeV/fm3 This is the only phase transition that occurred in the early universe that can be recreated in the lab

  3. The RHIC Experiments Approx 500 tracks result from a Au+Au ion collision RHIC

  4. RHIC runs (2001-2008) Beam species: p+p (polaized) d+Au Cu+Cu Au+Au Energy: sNN1/2=200 GeV Also @ 130 GeV 62 GeV 56 GeV 22 GeV (10 GeV) 130 GeV 200 GeV

  5. RHIC’s Two Major Discoveries STAR PRL86,402 (2001) PHENIX PRL88,022301(2002) • Strong Elliptic flow • Agree with ideal hydrodynamics • Low viscosity/entropy (h/s) • High pT suppression • Energy loss of quark/gluon • Very dense matter Based on these two major discoveries and other evidence, RHIC experiments concluded that that state of dense partonic matter is formed in A+A collisions at RHIC

  6. Highlights from more recent RHIC results • Scaling of v2 • Suppression at higher pT (up to 20 GeV/c) • Constraining model parameter from RAA • Modification of jet-correlations • J/y suppression • Heavy quark suppression and flow • Dileptons and photons Topics I don’t discuss due to time limitation • Low pT hadron spectra • Hadron ratios and thermal model • Enhanced (anti-)baryons • multi-strange baryons • v1 • v2/v4 scaling • c/b  m • g-jet correlation • HBT and source imaging • And more…

  7. Elliptic flow v2

  8. Scaling of v2 of hadrons • More data on v2(pT) of hadrons are accumulated • When v2/nq vs KET/nq (KET=transverse kinetic enery), all data points are on a universal curve, suggesting that v2 developed in partonic stage PRL98,162301(2007)

  9. More on the scaling of v2: phi flow PRL99, 052301 (2007) Phi meson (small interaction cross section) also follows the number of quark (nq) scaling.

  10. v2 of Direct photon and J/ye+e- Direct  v2 Min Bias Au+Au 200 GeV (Run 4) PHENIX preliminary First ever at RHIC, v2 - J/µ+µ- coming soon • Sign of direct  v2 (at high pT): • Positive == parton emission quenched • Negative == parton emission (Brems.) enhanced • At high pT, photon v2 is consistent with zero J/Psi coalescence ?

  11. High p T suppression RAA

  12. π0pT spectra at √sNN = 200 GeV RUN4 Au+Au arXiv:0801.4020 [nucl-ex] RUN2 Au+Au PRL91,072301 RAA measurements now extends to 20 GeV/c

  13. RAA of hadrons and direct photon (AuAu 200GeV) • A factor of ~5 suppression of p0 to ~20 GeV/c • Ncoll scaling for direct g • Same suppression pattern for p0andh: Consistent with parton energy loss and fragmentation in the vacuum • Smaller suppression for the f meson for 2<pT<5 GeV/c A factor of ~5 suppression to ~20 GeV !

  14. Quantitative analysis: contrain density parameters Comparison with GRV model: dNg/dy=1400 PRC77,064907

  15. RAA beam energy dependence (Cu+Cu)  Cu+Cu 22,62,200 GeV (Run 5) arXiv:0801.4555 Accepted in PRL g • Model calculations indicate quenching expected at sNN = 22 GeV, but Cronin effect dominates • Species dependence to probe space/time of suppression

  16. Di-jet correlations

  17. Dijet correlation Recoil jet Trigger Back-to-back peak due to di-jets is seen in two particle correlation Reconstruction of jets is difficult in A+A @ RHIC In central Au+Au collisions, the peak in the far side (Df ~ p) is suppressed, consistent with energy loss of the recoil jet.

  18. Modification of jet correlation • This is another big surprise: two particle of two high pT track (jet correlation) is modified in central Au+Au collisions. • Many theory attempts to explain this effect Au+Au PRL97,052301 (2006)

  19. Origin of the modification of jets? • An interesting interpretation of the modification is that it is Mach cone in the medium • Scattered parton travels faster than the speed of sound in the medium, causing a shock-wave • If this is the case, the opening angle can be related to the speed of sound in the medium…

  20. More detailed study of jet correlation D PRL98_232302

  21. Reaction plane dependence of di-jet correlation Shortest path length longest path length • Shape of the near-side peak is unchanged • Far-side shape strongly depends on the angle from the reaction plane • Stronger modification for longer pathlength in the dense matter

  22. Df*=0 Dq*=p PHENIX Preliminary Conical emission? Consistent with conical emission; STAR, 0805.0622 3-particle correlation analysis shows that the data is consistent with conical emission

  23. More surprize: the Ridge? Trigger Jet Ridge STAR QM2006 Bulk Medium In QM2006, STAR shows that there is “Ridge”, Enhancement in small Df and large Dh of leading particle This is the latest surprise in jet correlation in Au+Au and becomes a hot topics

  24. Is there “Ridge”? Apparently… • In QM2008, both PHENIX and PHOBOS shows that they also see “Ridge” • So far there is no consensus on the origin of this effect. • It is difficult to imagine that information can propagate for a wide rapidity gap. • My Speculation: Effect can be due to non-linear correlation between jets and v2?

  25. Screening by the QGP (An explicit test of deconfinement) If QGP is formed, J/y production is suppressed In normal vacuum, J/y particle is formed In QGP, J/y is destroyed by color screening

  26. J/y suppression in Au+Au PRL98_172301 • High statistics measurement of J/y in AuAu in wide rapidity range • Mid-rapidty J/y ee • Forward rapidty J/ymm • Strong suppression of J/y is observed • Consistent with the prediction that J/ys are destroyed in de-confined matter • Surprisingly, the suppression is stronger at forward rapidity than in mid-rapidity • J/y formation by recombination of charm pairs in deconfined matter? • But…we need to look the cold nuclear matter effect

  27. J/ in d+Au: Cold Nuclear Matter effect • Nuclear suppression factor RdAu of J/y in d+Au is measured and compared with models of CNM • Result: CNM = Shadowing(EKS)+Breakup Breakup = 2.8 mb • This is consistent with the J/y break up cross section at lower energy Breakup=4.2+/-0.5mb • If Breakup is obtained separately in forward and central region, larger value is prefered in forward J/ RdAu 200 GeV PRC77_024912 +1.7 -1.4 As SQM participants are aware of it, PHENIX is revisiting the systematic error in the break-up cross section.

  28. J/ RAA Cu+Cu and Au+Au J/ RAA 200 GeV • Approx 2x more J/ in Cu+Cu sample than Au+Au sample • More precise Npart<100 info • Curves show RAA prediction from ad hoc CNM fit to RdAu separately at y=0 and y > 1.2 • CNM from RdAu fit describes suppression well for Npart < 50. PRL101,12301(2008) RdAu constraints are not sufficientto say if suppression beyond cold nuclear matter is stronger at forward rapidity New Au+Au data (x4 statistics) and d+Au data (x30 statistics) obtained in 2007 and 2008 run can determine if the suppression really stronger beyond CNM in forward region.

  29. Heavy quark (charm and bottom) probe • Study medium effect in open charm and bottom production • Ideally, D or B meson should be measured, but for technical reason most of the measurement so far is done through electron decay channel. • From RAA and v2 of the electrons from heavy quark decays, the energy loss and the flow of heavy quarks are indirectly measured. • So far, ce and be are not separated e D, B c, b quark

  30. Heavy flavor production in pp (base line) Phys. Rev. Lett 97,252002 (2006) • Single electrons from heavy flavor (charm/bottom) decay are measured and compared with pQCD theory (FONLL) • The new data extends the pT reach to 9 GeV/c • FONLL pQCD calculation agree with the data • c e dominant in low pT be is expected to be dominant in high pT

  31. Large energy loss and flow of heavy quarks RAA of b,c e v2 of b,c e • Strong suppression of electron from c and b • Large energy loss of heavy quark • Large elliptic flow of electrons from c and b! • Heavy quark flows in the medium These results require very strong interaction between the dense matter and heavy quarks. Since the observed electron is mixture of ce (dominant) and be, we cannot determine the suppression or flow of be. Theoretical expectation is that the medium-quark interaction becomes weaker for heavier quark. Large energy loss and/or flow of b quark would be very interesting

  32. Heavy flavor electron RAA and flow PRL98,172301 (2007) • Two models describes strong suppression and large v2 • Rapp and Van Hee • Moore and Teaney • From model comparison, viscosity to entropy ratio h/s can be estimated DHQ× 2πT = 4 - 6 DHQ ~ 6 x h/(e+p) = 6 x h/Ts  h/s ~ (4/3 – 2)/4p • The estimate ofh/s is close to the conjectured bound 1/4p from AdS/CFT

  33. Comparison with other estimates R. Lacey et al.: PRL 98:092301, 2007 S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006 H.-J. Drescher et al.: arXiv:0704.3553 pTfluctuations STAR v2 PHOBOS v2 PHENIX & STAR conjectured quantum limit Estimates of h/s based on flow and fluctuation data indicate small value as well close to conjectured limit significantly below h/s of helium (4ph/s ~ 9)

  34. Bottom Measurement p+p 200 GeV Charm and bottom extracted via e-h mass analysis • Charm and bottom spectra are both by a factor  above FONLL pQCD calculations (but within the uncertainty) • STAR studied be/ce ratios in pp and obtained similar b/c ratios

  35. Next steps in Heavy quark measurements PRELIMINARY minimum-bias Rapp & van Hees, PRC 71, 034907 (2005) Run-7 Run-4 Higher statistics electron v2 measurement b/c separation (so far only in pp) Preliminary results STAR and PHENIX Does b quark also have large energy loss and/or flow? Recent data show large v2 at high pT where be dominates Silicon vertex tracker now under construction can answer this queston by separating be and ce in Au+Au collisions.

  36. Electromagentic probes (photon and lepton pairs) e+ e- g* g Photons and lepton pairs are cleanest probes of the dense matter formed at RHIC These probes has little interaction with the matter so they carry information deep inside of the matter

  37. submitted to Phys. Rev. Lett arXiv:0706.3034 submitted to Phys. Lett.B arXiv: 0802.0050 PHENIX low mass dielectrons p+p NORMALIZED TO mee<100 MeV low mass w AuAu f pp and AuAu normalized to p0 Dalitz region (~ same # of particles) p+p: agree with the expected background from hadron decays Au+Au: large Enhancement in 0.15-0.75 GeV/c2 J/y intermediate mass y’ pp

  38. PT Dependence of Au+Au Mee 0 < pT < 8 GeV/c 0 < pT < 0.7 GeV/c 0.7 < pT < 1.5 GeV/c 1.5 < pT < 8 GeV/c • Low Mass excess is a low pT enhancement • Huge excess at lowest pT • Excess reduced for higher pT This suggests that the low mass enhancement is from later phase of the reaction pp ee in later hadronic gas phase? PHENIX Preliminary

  39. Thermal(?) Photons from the hot matter thermal: Decay photons (background) hard: If the dense matter formed at RHIC Thermailzed, it should emit “thermal radiation”. The temperature of the matter can directly measured from the spectrum of thermal photon. Measurement is difficult since the expected signal is only 1/10 of photons from hadron decays

  40. Enhancement of almost real photon pp Au+Au (MB) arXiv:0804.4168 • Low mass e+e- pairs (m<300 MeV) for 1<pT<5 GeV/c • p+p: • Good agreement of p+p data and hadronic decay cocktail • Small excess in p+p at large mee and high pT • Au+Au: • Clear enhancement visible above for all pT 1 < pT < 2 GeV 2 < pT < 3 GeV 3 < pT < 4 GeV 4 < pT < 5 GeV

  41. Determination of g* fraction, r Direct g*/inclusive g* is determined by fitting the following function for each pT bin. Reminder : fdirect is given by Eq.(1) with S = 1. r : direct g*/inclusive g* • the mass spectrum follows the expected 1/m behavior of photon internal conversion • Determine the fraction r of the “direct photon” component from the fit

  42. Fraction of direct photons Fraction r of direct photons p+p: Consistent with NLO pQCD favors small μ Au+Au: Clear excess above pQCD Au+Au (MB) p+p μ = 0.5pT μ = 1.0pT μ = 2.0pT NLO pQCD calculation is provided by Werner Vogelsang

  43. Direct photon in p+p, Au+Au arXiv:0804.4168 • The p+p data agrees with NLO pQCD predictions • For Au+Au there is a significant low pT excess above scaled p+p expectations • Excess is exponential in shape with inverse slope T~ 220MeV • Thermal photons from hydrodynamical models with Tinit=300 – 600MeV at t0=0.6-0.15fm/c are qualitative agreement with the data (see next) exp + TAA scaled pp Fit to pp NLO pQCD (W. Vogelsang)

  44. Theory comparison Thery compilation by D. d’Enterria and D. Peressounko EPJC46, 451 (2006) • Hydrodynamical models are compared with the data D.d’Enterria &D.Peressounko T=590MeV, t0=0.15fm/c S. Rasanen et al. T=580MeV, t0=0.17fm/c D. K. Srivastava T=450-600MeV, t0=0.2fm/c S. Turbide et al. T=370MeV, t0=0.33fm/c J. Alam et al. T=300MeV, t0=0.5fm/c • Hydrodynamical models are in qualitative agreement with the data

  45. Summary • Huge amount of data are accumulated from RHIC in the past 8 years • Many interesting phenomena are observed • Strong elliptic flow of light hadrons and heavy quarks • Strong suppression of high pT jets • Modification of jet correlation • Strong suppression of J/y • Energy loss and flow of heavy quarks • Enhanced production of lepton pairs and photons • These observations are consistent with formation of thermalized, high temperature, high density partonic fluid

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