Universal features of QCD dynamics in hadrons & nuclei at high energies

1. Universal features of QCD dynamics in hadrons & nuclei at high energies Raju Venugopalan DNP (APS/JPS) meeting, Hawaii, October 13, 2009

2. High Energy QCD • QCD is the “nearly perfect” fundamental theory of the strong interactions(F.Wilczek, hep-ph/9907340) • We are only beginning to explore the high energy, many body dynamics of this theory What are the right effective degrees of freedom at high energies? -- gluons & sea quarks, dipoles, pomerons, strong fields? How do these degrees of freedom interact with each other and with hard probes? -- Multi-Pomeron interactions, Higher Twist effects, Saturation/CGC -- Rapidity Gaps, Energy loss, Multiple Scattering, Color Transparency -- Glasma, Quark Gluon Plasma What can this teach us about confinement, universal features of the theory (infrared fixed point?) -- hard vs soft Pomerons, Strong Fields, in-medium hadronization -

3. High Energy QCD-the role of Glue Localized energy fluctuation of Gluon Field (D. Leinweber) Self-interacting carriers of the strong force Dominate structure of QCD vacuum MILC Coll.: hep-lat/0304004 Hadron mass spectrum vs quenched lattice results full QCD Quenched QCD Nearly all visible matter in the universe is made of Glue

4. Measuring Glue: what are our options? Gluon jet event in e+e- collisions at LEP • p+A and e+A provide complementary information on role of glue • Need both to test what’s universal and what’s not in QCD processes • Some final states differ dramatically (diffractive/exclusive states) Nothing matches DIS for precision-vast majority of world data for pdfs (especially for glue) from DIS

5. Inclusive DIS Measure of resolution power Measure of inelasticity Measure of momentum fraction of struck quark quark+anti-quark mom. dists. gluon mom. dists

6. HERA data on inclusive DIS Gluon distribution from scaling violations of F2 Proton is almost entirely glue by x=0.01 for Q2 = 10 GeV2 Parton Density x= fraction of momentum of hadron carried by parton

7. HERA data on inclusive DIS # partons per unit rapidity For Q2 ≤ 5 GeV2, leading twist (“parton gas”) description problematic. Sign of higher twist (multi-parton correlation) effects? Recent HERA data on FL (H1: Q2 = 12-90 GeV2 ; ZEUS Q2 = 24-110 GeV2) EIC can add significantly to world FL data set -- even for protons. Important test of QCD evolution Golec-Biernat, Stasto, arXiv: 0905.1321

8. Resolving the hadron in the Bjorken limit of QCD -DGLAP evolution increasing Q2 But… the phase space density decreases-the proton becomes more dilute Important for precision/ beyond standard model physics

9. Resolving the hadron in the Regge-Gribov limit of QCD -BFKL evolution - Large x IMF picture: Gluon phase space grows - saturates at occupation # f = - Small x Rest frame picture: Scattering amplitude is unity…

10. Large x - bremsstrahlung linear evolution (DGLAP/BFKL) Small x -gluon recombination non-linear evolution (BK/JIMWLK) Mechanism of gluon saturation in QCD Gribov,Levin,Ryskin Mueller,Qiu p, A Saturation scale QS(x) - dynamical scale below which non-linear (“higher twist”) QCD dynamics is dominant

11. The Color Glass Condensate McLerran, RV Jalilian-Marian,Kovner,Weigert Iancu, Leonidov,McLerran In the saturation regime: Strongest fields in nature! • CGC: Classical effective theory of QCD describing • dynamical gluon fields + static color sources in non-linear regime • Novel renormalization group equations (JIMWLK/BK) • describe how the QCD dynamics changes with energy • A universal saturation scale QS arises naturally in the theory

12. Saturation scale grows with energy Y=ln(x0/x)0,1,3,9 unintegrated gluon dist. from NLL RG evolution QS(x) Bulk of high energy cross-sections: obey dynamics of novel non-linear QCD regime Can be computed systematically in weak coupling Exact analogy to physics of “pulled” travelling wave fronts in stat. mech. Munier,Peschanski

13. Evidence from HERA for geometrical scaling Golec-Biernat, Stasto,Kwiecinski   = Q2 / QS2 F2 D VM, DVCS V F2D Marquet, Schoeffel hep-ph/0606079 • Scaling seen for F2D and VM,DVCS for same QS as F2 Gelis et al., hep-ph/0610435 • Scaling confirmed by “Quality factor” analysis • Recent NLO BK analysis: Albacete, Kovchegov,hep-ph-0704.0612 Recent caveats: Avsar, Gustafson, hep-ph/0702087

14. q z * r 1-z q P Inclusive DIS in saturation models • = 0.3; x0 = 3* 10-4 Machado, hep-ph/0512264 Kowalski, Teaney

15. Saturation Models-excellent fits to HERA data Kowalski et al., hep-ph/0606272 Also see Forshaw et al. hep-ph/0608161

16. Inclusive diffraction MX “Pomeron” Rapidity Gap Big surprise at HERA:~ 15% of all events are hard diffractive (MX > 3 GeV) events • In rest frame: 50 TeV electron hits proton - in 1/7 events proton remains intact • Diffractive structure functions in DIS measure quark and gluon content of Pomeron Collins

17. Caveat: Saturation scale extracted from HERA data inconsistent with model assumptions ? Model assumes Typical sat. scale is rather low... QS2 << 1 GeV2

18. Saturation scale grows with A High energy compact (1/Q < Rp) probes interact coherently across nuclear size 2 RA - experience large field strengths c ~ 1 in saturation model fit to HERA extrapolated to nuclei Kowalski, Lappi, RV Enhancement of QS with A => non-linear QCD regime reached at significantly lower energy in A than in proton

19. Evidence of geometrical scaling in nuclear DIS Freund et al., hep-ph/0210139 Geometrical scaling Nuclear shadowing: • Data scale as a function of  = Q2 / QS2

20. 600 1200 Krasnitz, RV Evidence of non-linear saturation regime @ RHIC ? Global multiplicity observables in AA described in CGC models: Input is QS(x,A) PHOBOS central Au+Au mult. vs models Kharzeev,Levin,Nardi

21. DA: Kharzeev,Kovchegov,Tuchin Albacete,Armesto,Salgado,Kovner,Wiedemann Blaizot, Gelis, RV D-Au pt spectra compared to CGC prediction Hayashigaki, Dumitru, Jalilian-Marian Forward pp @ RHIC as well Boer, Dumitru, PRD 74, 074018 (2006) Review: Jalilian-Marian, Kovchegov, hep-ph/0505052

22. Natural explanation for limiting fragmentation + deviations in CGC Jalilian-Marian Extrapolation of BK-fit to RHIC LF data to LHC dn/dy|_{y=0} = 1500-2250 in A+A at LHC Gelis,Stasto, RV, hep-ph/0605087

23. Terra Incognita Why Physics at an e+A collider is interesting Not your grand aunt’s e+A: world’s first such collider, first measurements of a range of final states… eg. rapidity gaps, jets, impact parameter dependent distributions • Large x and Q2 : Precision study of propagation of colored • probes in extended QCD medium. QCD showering and • fragmentation in nuclei • Small x: Explore physics of strong, non-linear color fields

24. What are the measurements? • Would like answers to: • What is the momentum distribution of gluons in matter • What is the space-time distribution of gluons in matter • How do fast probes interact with the gluonic medium? • What is the nature of color neutral exchanges (Pomerons) Tools/Measurements: • Precision inclusive measurements of structure functions : : (Inclusive diffraction) • Semi-inclusive measurements of final state distributions • Exclusive final states Multiple handles: x, Q2, t, MX2 for light and heavy nuclei

25. Gluon distribution from FL @ eRHIC Eskola,Paukkunen,Salgado EIC: 10 GeV + 100 GeV/n - estimate for 10 fb-1 Quark and Glue contribution to Hadron-hadron inclusive Cross-section

26. Inclusive diffraction • In pQCD, expect exponential suppression of large gaps • -- parametrize data with diffractive structure functions • which obey QCD evolution…not universal • In CGC, diffractive structure functions depend on universal dipole cross-section squared. Diffractive cross-section ~ 25% of total cross-section! Large  = small MX Small  = large MX Interesting pattern of enhancement and suppression-can be tested Kowalski,Lappi,Marquet,RV

27. Exclusive final states in DIS Brodsky et al. Frankfurt,Koepf,Strikman In the dipole model: Kowalski,Motyka,Watt Extract b dist. of glue In nuclei? Claim: can extract t dependence in photo-production of J/ down to t = 10-4 GeV2 Caldwell-Kowalski

28. Universal gluodynamics & energy dependence of QS A.H. Mueller, hep-ph/0301109 Small x QCD RG eqns. predict (fixed b) QS approaches universal behavior with increasing energy (Y) for all hadrons and nuclei -can the approach to this behavior be tested ?

29. In eA DIS, cleanly access cross-over region from weak field to novel strong field QCD dynamics ? Weak field regime Q2 >> QS2 Strong field regime Q2 << QS2 Qualitative change in final states: eg., 1/Q6 1/Q2 change in elastic vector meson production McDermott,Guzey,Frankfurt,Strikman; Review: Frankfurt, Strikman, Weiss

30. Semi-inclusive DIS Virtual photon with short coherence length scatters off quark or gluon (photon-gluon fusion) in medium - jet propagates through medium Vastly extended reach at EIC relative to HERMES, Jlab, EMC Precision studies of heavy quark energy loss Accardi,Dupre,Hafidi,

31. Glasma Initial Singularity sQGP - perfect fluid Color Glass Condensates Hadron Gas What does a heavy ion collision look like ? t

32. Glasma Initial Singularity sQGP - perfect fluid Color Glass Condensates Hadron Gas What does a heavy ion collision look like ? t

33. Before: transverse E & B “Weizsacker-Williams fields generate Chern-Simons topological charge parallel color E & B fields Lappi,McLerran,NPA 772 (2006) Kharzeev, Krasnitz, RV, Phys. Lett. B545 (2002) Glasma flux tubes from small x dynamics Krasnitz,Nara, RV; Lappi After: boost invariant Glasma flux tubes of size 1/QS

34. Au+Au 200 GeV, 0 - 30% PHOBOS preliminary Imagining the Glasma through long range rapidity correlations Causality dictates:  < 1 fm for y > 4 At LHC can probe color field dynamics for  << 1 fm… Very sensitive to gluon correlations in wave fn.

35. Lattice Gauge Theory Condensed Matter Physics High Energy Physics (LHC,LHeC Cosmic Rays) (B-E Condensates, Spin Glasses Graphene) Theory @ EIC

36. Inclusive Diffraction-II Impact parameter dipole (CGC) models give -sq. fits ~ 1 to HERA e+p inclusive and diffractive cross-section: H. Kowalski, C. Marquet, T. Lappi and R. Venugopalan, Phys. Rev. C 78, 045201 (2008). • = parton mom./Pomeron mom. xP= Pomeron mom./ Hadron mom.

37. Estimates of the saturation scale from RHIC A

38. Turbulent “thermalization” may lead to “anomalously” low viscosities Asakawa, Bass, Muller; Dumitru, Nara, Schenke, Strickland • Significant energy loss in Glasma because of synchroton like radiation? Shuryak, Zahed; Zakharov; Kharzeev The unstable Glasma Romatschke, RV:PRL 96 (2006) 062302 • Small rapidity dependent quantum fluctuations of the LO Yang-Mills fields grow rapidly as • E and B fields as large as EL and BL at time Possible mechanism for rapid isotropization Problem: collisions can’t ‘catch up’

39. NCS= -2 -1 0 1 2 + Topological fluctuations -sphaleron transitions in Glasma External (QED) magnetic field L or B STARPreliminary = Possible experimental signal of charge separation (Voloshin, Quark Matter 2009) Chiral magnetic effect P and CP violation: Chiral Magnetic Effect Kharzeev,McLerran,Warringa Effect most significant, for transitions at early times

40. Semi-inclusive DIS At small x: Hadron distributions and multiplicities sensitive to QS(x,A) Kang,Qiu Ratio to x = 10-2 proportional to ratio of QS2(x,A) Need more quantitative studies for EIC kinematics Marquet,Xiao,Yuan

42. Solution: for early times (t  1/QS) -- n-gluon production computed in A+A to all orders in pert. theory to leading log accuracy Gelis, Lappi, RV; arXiv : 0804.2630, 0807.1306, 0810.4829 Forming a Glasma in the little Bang Glasma (\Glahs-maa\):Noun:non-equilibrium matter betweenColor Glass Condensate (CGC)& Quark Gluon Plasma (QGP) • Problem: Compute particle production in QCD with strong time dependent sources

43. New window on universal properties of the matter in nuclear wavefunctions Iancu, RV, hep-ph/0303204 A Can we quantify the various regimes ?

44. Strong color fields may be more accessible in eA collisions relative to ep Nuclear profile more uniform-can study centrality dependence of distributions

45. Outline of talk • Whither the “perfect” theory ? - QCD at high energies • QCD coherence at small x => Universality - Saturation in hadrons & nuclei; the Color Glass Condensate picture • Exploring the structure of high energy nuclei with EIC - enteringterra incognita • From Glue to Glasma & QGP - how multi-parton correlations in nuclei generate extreme states of quark-gluon matter