Probing Dense Partonic Matter at RHIC

1. Probing Dense Partonic Matter at RHIC News from PHENIX Barbara Jacak for the PHENIX Collaboration Feb. 8, 2004

2. Outline • Characterizing plasmas with PHENIX • Initial state • pQCD via direct photons • Shadowing via RdA in d+Au • Initial state multiple scattering in d+Au • Thermalization • Elliptic flow dependence on particle type, √s • F production • Charm flow • Probes of the partonic state • Heavy quark energy loss • Away-side jet modification • What baryons tell about coupling to the medium

3. Properties of plasmas • Plasma physicists always want to know (and so do we) • pressure, viscosity, equation of state, • thermalization time & extent • determine from collective behavior at RHIC • Other useful plasma properties • radiation rate, collision frequency, conductivity, opacity, Debye screening length • what is interaction s of q,g in the medum? • need short wavelength strongly interacting probe • transmission probability • jet quenching via RAA • high momentum q,g are our “external” probes!

4. Collision vertex and centrality • Beam-Beam Counters (BBC) • Zero Degree Calorimeters (ZDC) • Tracking of Charged particle • Drift Chambers (DC) • Pad Chambers (PC1, PC2, PC3) • p, K, p, d, ... ID by Time-Of-Flight • Start timing from BBC • Stop timing from High resolution TOF detectors (TOF) TOF from Lead Scintillator EMCal (PbSc) • Electron ID • Ring Image Cherenkov (RICH) detectors • EMCal (PbSc, PbGl) • Photon (p0, h, ...) • EMCal (PbSc, PbGl) • Muon • Muon Tracker (MuTr) Cathode-strip readout chamber • Muon Identifier (MuID) Streamer (Iarocci) tube and steel PHENIX

5. Direct photons (p+p) see talk of S. Bathe LO NLO: Bremsstrahlung pQCD works!

6. Direct photons in Au+Au • pQCD works too (with nuclear Sa/A(xa,r) , TA(r) + observed p0s) •  can reliably calculate rate & distribution of short wavelength probes of hot, dense partonic matter!

7. kT smearing? • g data allow kT smearing • But, certainty awaits higher statistics (currently being analyzed)

8. Charm production also calculable* nucl-ex/0409028 * total yield scales with Ncoll. I will return to charm again ** there is a long-standing problem with sc

9. Charm via single e± in p+p PHENIX preliminary

10. (PHENIX compared with ISR results for p+p) PHENIX PRELIMINARY Single e± in √sNN = 62.4 GeVAu+Au Compatible with <Ncoll> scaling

11. Nuclear initial state effects • shadowing, saturation, multiple initial state scattering • PHENIX has a wide range of d+Au data • tools • shadowing via heavy quark or high pT hadron production • PHENIX can probe saturation (super-shadowing…) • via rapidity dependence of hadron production • Initial state multiple scattering via dependence of hadrons upon number of collisions per participant

12. d+Au: Cronin Effect (RdA>1): Multiple Collisions broaden pT spectrum Nuclear medium modifies initial state • Probe cold nuclear matter by varying number of collisions. • Shadowing + initial semi-hard scatterings • (Accardi, Gyulassy) reproduce the data PRELIMINARY Very little room for additional dynamical shadowing at mid-y Phys. Lett. B586, 244 (2004)

13. PRELIMINARY Cronin effect for protons greater than for p would not expect this from initial state partonic multiple scattering!

14. “Thermal Fragmentation (one jet) Thermal+Shower Different jets. Need something else too… • Recombination?! “ PROTON PRODUCTION IN D+AU COLLISIONS AND THE CRONIN EFFECT; HWA & YANGPhys.Rev.C70:037901,2004

15. d Au Muon arms probe forward rapidity see talk of Anuj Purwar MUON ARMS CAN DETECT: *stopped muons from hadron decays * hadrons which punch thru absorber and interact in m arm study central vs. peripheral in d+Au

16. d+Au central/peripheral PTH = Punch Through HadronsHDM = Hadronic Decay Muon 1.5 < pT (GeV/c) < 4.0 PHENIX nucl-ex/0411054 x~0.2-0.3 d Au Au x~0.2x10-3 Suppression at forward η and enhancement in the back η.

17. Compare with BRAHMS nucl-ex/0411054 Overall consistent.

18. Color glass condensate? Kharzeev, hep-ph/0405045 Hadron Punch Through Centrality, pT dependence ~ correct Slightly better agreement with BRAHMS data “normal” shadowing cannot explain (R. Vogt hep-ph/0405060) …could be sign of CGC

19. But, recombination lurks… Hwa, Yang and Fries nucl-th/0410111 • shower + medium recombination → reductes soft parton density on deuteron side • Can explain fward-bward asymmetry AND RCP (protons) > RCP (mesons) at midrapidity. BRAHMS data

20. fà e+e- @ d – Au, √s = 200 GeV Mixed Background Counts per 10 MeV/c2 S ~ 120 S/B = 1/4 e+e- invariant mass (GeV/c2) f: does it fit with the non-strange mesons? see talks of D. Pal and D. Mukhopadhyay f  K+K- Au + Au @ √SNN = 200 GeV nucl-ex/0410102 Au+Auwidth & centroid as in PDG

21. Au + Au @ √sNN = 200 GeV sNN = 200 GeV d+Au, Min. Bias 10-1 PHENIX preliminary Au + Au @ √sNN = 200 GeV   e+e- 10-2   K+K- 10-3 10-4 10-5 0 0.511.522.5 3 mT – mass [GeV/c2] f spectra & radial flow nucl-ex/0410102 • d+Au f yields & slopes: KK and ee consistent • Au+Au: f slopes nearly independent of Npart but – this is at high pT consistent with blast wave fit to p, K, p Tfo = 109 ± 2.6 MeV, bT,max = 0.77 ± 0.004

22. p0:extend to higher pT v2 and scaling with nquark 62.4 GeV Au+Au: preliminary 200 GeV Au+Au, charged p,K,p PRL91, 182301 (2003) p0 : work in progress stat. error only sys. error <20% (62GeV) 15% (200GeV) v2 /nquark 62.4 GeV Au+Au: scaling, v2/quark similar to 200 GeV pT /nquark [GeV/c]

23. Elliptic flow dv2/dpT vs √s Collision energy dependence nucl-ex/0411040 • smooth rise of v2 from AGS to SPS to RHIC energies. • v2 saturates: evidence for soft EOS? how soft?

24. Are the v2 trends hydrodynamic? • use Buda-Lund model (nucl-th/0402036) • particle emission from ellipsoidal expanding source • v2 in terms of Bessel functions from Boltzmann distrib. • converting to transverse “rapidity”: • so v2 should have the form: we then define a “fine structure” variable

25. data look like hydro! (kaons a mystery, still) scaling with e also seen supports scenario of rapid thermalization Kolb, et al The data transform:

26. proton pion Caveat: v2 & spectra vs. hydrodynamic models nucl-ex/0410003 Hydro models: Teaney (w/ & w/o RQMD) Hirano (3d) Kolb Huovinen (w/& w/o QGP)

27. How about heavy quarks? do they flow? nucl-ex/0502009 • PHENIX measures v2 of non-photonic e± • electron ID in Au+Au via RICH + EMCAL • measure and subtract photonic sources using converter YES v2≠ 0 at 90% confidence level data consistent with heavy q thermalization also “predicted” by Teaney *but large errors; run4 will tell Greco,Ko,Rapp. PLB595, 202 (2004)

28. Short wavelength probes of partonic matter coupling to the medium probes medium properties • HOW is jet fragmentation modified by the medium? • do heavy quarks lose energy as the light quarks do? • Kharzeev & DokshitzerPLB519, 199 (2001): eloss smaller • dead cone due to large mass decreases gluon radiation • by ~20% at moderate pT • Djordjevic, Gyulassy, Wickshep-ph/0410372: smaller • dead cone, charm pT spectrum & B contribution cause RAA ~ 0.6-0.8 for 2.5< pT <4 GeV/c • Cronin effect & collective flow also important • Armesto, Dainese, Salgado, Wiedemanhep-ph/0501225 :smaller • dead cone, g vs. q eloss differences → smaller RAA for c • Teaney: eloss significant if charm thermalizes!

29. Non-photonic single electron spectra

30. Use p+p single e± as reference → RAA RAA clear evidence for energy loss of charm quarks in central Au + Au! (NB likely to also be some e± from B decays) pT (GeV/c)

31. RAA pT (GeV/c) Consistent with light quarks? non-pert. effects on “normal” g radiation data say: same transport coefficient, smaller hadron suppression q consistent w/ light quark eloss

32. jet probes of the medium see talk of N. Ajitanand Hard scattered partons traverse the interesting stuff Energy loss by induced gluon radiation where does the energy go? Modification of fragmentation outside the medium??  recombination with medium partons  radiated gluons nearby!

33. correlation functions of two high pT hadrons Elliptic flow component measured vs. BBC reaction plane

34. decompose to get jet pair distribution Away-side jets broadened non-Gaussian! ~2sdip at p& peak at 1.25 rad around hard parton thru medium integrating entire away side recovers jet partners Casalderry, Shuryak, Teaney say 1.1 rad cone hep-ph/0411315

35. identify triggers, count partners nucl-ex/0408007 Jet partner likely for trigger baryons as well as mesons! Same side: slight decrease with centrality for baryons Dilution from boosted thermal p, pbar? Away side: partner rate as in p+p confirms jet source of baryons! “disappearance” of away-side jet into narrow angle for both baryons and mesons

36. baryon Meson trigger Fries, Bass & Mueller nucl-th/0407102 What’s going on? Radiated gluons are collinear (inside jet cone) Increases partner yield Thermal quark recombination Dilutes jet partner yield

37. Jet partner distribution on trigger side nucl-ex/0408007 Corrected to jet yield according to fragmentation symmetric in f,h Partner spectrum flatter, as expected for jet source Partners soften in most central collisions Jet partners Inclusive

38. Compare to hard-soft recombination p trigger & p associated Hwa & Yang nucl-th/0407081 Soft-hard recomb. also explains baryon Cronin effect! No jet-correlated medium flow

39. Conclusions • Direct g & hard processes in AuAu calculable in pQCD • we observe nuclear shadowing at RHIC • no room for saturation at mid-y; forward: could be • baryon mysteries already present in d+Au • Hadron v2 trends support rapid thermalization hypothesis • theorists have homework to see how soft is EOS • heavy quarks do flow (and thermalize…) • Heavy quarks lose energy in the medium! • jet fragmentation is modified; lost energy excites the medium • baryon formation in/near medium in A+A and d+A • Opacity/collision frequency, screening length await run4 analysis completion (+ theory work!) • radiation rate (low mass leptons, soft g) → PHENIX upgrades

40. backup slides

41. Compare to Au+Au PRELIMINARY • p RAA as expected in Au+Au; d+Au slightly enhanced • p RAA scales with Ncoll in Au+Au, but s higher than p+p

42. Turn to nuclear collisions: single particles PRELIMINARY h/p0 ratio shows baryons enhanced for pT < 5 GeV/c

43. Hor. bar : stat. err. Box : total sys. err. dN/dy (dN/dy) / (2<Npart> ) 200 GeV d+Au (preliminary) 200 GeV Au+Au w/ centrality cut 200GeV Au+Au Min. Bias 0 100 200 300 0 100 200 300 <Npart> <Npart> yields nucl-ex/0410102 rapid rise in f/participant in peripheral collisions then ~ constant per participant - as for kaons

44. Interacting Hadrons Stopped muons (peak) Interacting Hadrons (tail) MuID Gap (Layer) 0 1 2 3 4 1 GeV  3 GeV  3 GeV  Hadrons interactelectromagneticallyAND strongly. steel

45. Muon detector p m absorber Muons from Light Meson Decays • Muon event collision vertex distribution • D c = 0.03 cm Decays before absorber •  c = 780 cm Most are absorbed, but some decay first • K c = 371 cm Most are absorbed, but some decay first γcτ >> 80cm → Decay Probability nearly constant between nosecones η > 0 Detector Muon pT ~ 0.85 parent pT

46. FONLL Predictions • Mateo Cacciari provided a prediction using the Fixed Order Next Leading Logarithm pQCD approach • His calculation agrees perfectly with our “poor man’s” HVQLIB+PYTHIA predictions • Data exceed the central theory curve by a factor of 2-3 • Possible explanations: • NNLO contribution • Fragmentation mechanisms need to be studied in more details

47. centrality dependence? • need to complete analysis of run4 data… • first glimpse

48. Pions in 3 detectors in PHENIX • Charged pions from TOF • Neutral pions from EMCAL • Charged pions from RICH+EMCAL Cronin effect gone at pT ~ 8 GeV/c

49. Measure with mixed events; Collective flow causes another correlation in them: associated particles with non-flow angular correlations -> jets! B(1+2v2(pTtrig)v2(pTassoc)cos(2)) Subtract the underlying event includes ALL triggers (even those with no associated particles in the event) combinatorial background large in Au+Au! CARTOON 1 dN flow+jet Ntrig d flow jet

50. 2 particle correlations Select particles with pT= 2.5-4.0GeV/c Identify them as mesons or baryons via Time-of-flight Find second particle with pT = 1.7-2.5GeV/c Plot distribution of the pair opening angles; integrate over 55°