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CGC: Lessons for eA from RHIC

This article explores the concept of parton saturation and the Color Glass Condensate (CGC) theory in the context of heavy ion collisions at RHIC. It discusses the effects of parton saturation on parton density, recombination, hadronization, and chemical freeze-out. The article also examines the pseudorapidity density, the predictions of parton saturation for AA collisions, and the QCD phase diagram puzzle.

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CGC: Lessons for eA from RHIC

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  1. STAR CGC: Lessons for eA from RHIC Mark D. Baker Mark D. Baker

  2. Parton saturation (& CGC) • Parton density cannot grow indefinitely. • Recombination (ggg, qgq) kicks in at low x. See e.g. Iancu, Venugopalan hep-ph/0303204 for a recent review History: GLR, Mueller-Qiu, M-V, BK, JIMWLK & many more... Mark D. Baker

  3. time Hadronization & Chemical freeze-out Kinetic freeze-out elastic interactions QGP? inelastic interactions CGC? space blue beam yellow beam Accessing saturation at RHIC AA Nuclei (CGC) partonic system  frozen out hadrons Theory Modeling ansatz: “final state” effects are essentially trivial. Let’s see what happens... Mark D. Baker

  4. Pseudorapidity density g g g g g g Mark D. Baker

  5. Parton Saturation “predicts” AA Kharzeev & Levin, nucl-th/0108006 # of gluons l fixed by HERA data: xG(x)~x-l& t ~ Q2 xl Describes dN/dh shape! PRL 87 (2001) Fit PHOBOS data at 130 GeV to set c, Qs Mark D. Baker

  6. Saturation Works at 200 GeV L. McLerran, DNP 2001 nucl-ex/0112001 See now: Phys. Rev. Lett. 88, 202301(2002) h l fixed by HERA data: xG(x)~x-l& t ~ Q2 xl Describes dN/dh energy evolution! Mark D. Baker

  7. Color Glass Condensate at RHIC • Energy and Npart evolution work over a broad range. Mark D. Baker

  8. More CGC at RHIC Iancu, Venugopalan hep-ph/0303204 Not just Kharzeev! Mark D. Baker

  9. early universe T RHIC & LHC Quark Matter TC~170MeV (2*1012 K) Hadron Resonance Gas Color Superconductor Nuclear Matter neutron stars mB 940MeV 1200-1700 MeV The QCD Phase Diagram Puzzle: Why is the evolution of this explosive, jet-eating, strongly interacting matter “trivial”? Or at least isentropic? deconfinement & chiral symmetry Mark D. Baker

  10. Hardtke, QM2002 Interlude: Jet Quenching Breaking news at EIC 3/2002 scaled pp quenching See PRL 90 (2003) 082302 • See now • PRL 88 (2002) 022301 • arXiv:nucl-ex/0207009 • PRL 91 (2003) 072301 • arXiv:nucl-ex/0308006 Mark D. Baker

  11. Npart scaling: MAXIMAL jet quenching? Ncoll *S / V ~ Npart4/3 / L ~ Npart Only jets produced on the surface survive! PHOBOS, PLB 578 (2004) 297 2 Ratio Au+Au 200 GeV 1 UA1 pp (200 GeV) 0 Npart Normalize by Npart/2. Divide by the value at Npart=65 Mark D. Baker

  12. Parton Saturation: another explanation? KLM: PLB 561 (2003) 93 Requires strong saturation (large Qs) Nice summary from Jamal Jalilian-Marian (QM04) • RAA < 1: initial state? • BFKL anomalous dim.: 1/Q2 ---> (1/Q2)0.6 • Approximate Npart scaling • 2 ---> 1 processes • (reduced back to back correlations) Particle Yield/<Npart/2> Mark D. Baker

  13. IF saturation is strong enough to cause initial state “jet quenching” THEN it should show up as suppression in central dAu (RdAu ~ 70%) NO! The saturation theory overreached pA dA For AuAu: • Midrapidity jet-quenching is a “final state effect”. • The matter produced is very dense and strongly interacting. Accessing saturation at RHIC. (2) Mark D. Baker

  14. Results from dAu near mid-rapidity Au+Au and d+Auscale differentlyrelative to Ncoll PRL91, (2003), 072302-5 Mark D. Baker

  15. Saturation in dA continued PHOBOS, nucl-ex/0311009, submitted to PRL KLN (Jan. 2004) Claim: saturation ~OK for soft particles Mark D. Baker

  16. Latest KLN result March 8, 2004 arXiv:hep-ph/0212316 v4 Mark D. Baker

  17. Next idea: Go forward! g g Increasing y Note: PHOBOS RdA(h=1) < RHIC RdA(h=0)! Mark D. Baker

  18. CAVEAT: Shape not perfect Spectra in d+Au for h>0 Brahms DNP - submitted to PRL G. Veres QM04 (PHOBOS) This could be the CGC! Mark D. Baker

  19. What about backwards rapidity? Phenix Brahms Not exactly in violation of theory, but shouldn’t really be in saturation region Mark D. Baker

  20. Soft particle enhancement/suppression pattern Miklos Gyulassy QM2004 - courtesy of Nouicer, Steinberg Npart Mark D. Baker

  21. Where is midrapidity? Soft particles see full participant zone Systematic errors are not shown Hard, rare partonic collisions should just see NN frame Mark D. Baker

  22. “Hard” & “soft” particles behave similarly Phenix Brahms Phobos dN/dh dA/pp scaled by 1.4 /(Npart/2) “high pT” suppression (& enhancement) in dAu may interact with the bulk participant system or may lose rapidity through multiparticle collisions. Mark D. Baker

  23. Summary • Heavy ion results do lend support to the ideas of parton saturation (CGC). • dN/dh systematics for AA • dN/dh for dA (~) • “High” pT suppression in forward dA • Puzzles • How can a theory about initial state gluons describe hadrons that have been through so much? • Is it an accident that the RdA(h) enhancement/suppresion pattern is the same for “hard” and “soft” particles? • eA data will (eventually) be valuable. Mark D. Baker

  24. Extras Mark D. Baker

  25. Comparing AuAu to pp A L~A1/3 # of NN collisions ~A4/3 (formally Glauber TAA(b)) # of participating nucleons: 2A Mark D. Baker

  26. “Tau scaling” in DIS 1000 Statso et al., PRL 86 (2001) 596 stot g*p (mb) 100 Fit l=0.25 10 1 0.1 10-3 1 103 t Q2xl Mark D. Baker

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