• Little Bang

1. The Science Case for RHIC II Barbara Jacak Users’ Meeting June 8, 2006 •Little Bang Discover January 2002

2. Summary of RHIC II Science Workshops* We have found an amazing new (old) form of matter at RHIC! It follows ~ perfect fluid dynamics, is opaque to colored probes, hadron spectra governed by valence quark content, shows evidence for saturation of gluons in initial state. Fundamental questions for RHIC in the next decade: • What are the phases of QCD Matter? • What is the wave function of the proton? • What is the wave function of a heavy nucleus? • What is the nature of non-equilibrium processes in a fundamental theory? * editors: Carl Gagliardi and Tony Frawley see http://www.bnl.gov/physics/rhicIIsciencefor reports

3. I will discuss in terms of conventional plasma studies A paradigm for interpretation of present results and organizing our ideas about going forward Krishna’s talk Plasma Physics of the Quark Gluon Plasma

4. plasma • ionized gas which is macroscopically neutral • exhibits collective effects • interactions among charges of multiple particles • spreads charge out into characteristic (Debye) length, lD • multiple particles inside this length • they screen each other • plasma size > lD • “normal” plasmas are electromagnetic (e + ions) • quark-gluon plasma interacts via strong interaction • color forces rather than EM • exchanged particles: g instead of g

5. Plasma properties & some “diagnostics” • moments of the distribution function of particles f(x,v) • 0th moment → particle density (n) • higher moments are <velocity> & temperature, • pressure tensor, heat flux tensor • opacity/transmission is a probe of choice • Transport properties (e.g. diffusion, viscosity) • Screening • Collective Effects • hydrodynamic expansion, shock propagation • → density correlations inside plasma • Radiation • bremsstrahlung, blackbody, collisional and recombination • Plasma oscillations, instabilities

6. Plasma properties & “diagnostics” • moments of the distribution function of particles f(x,v) • 0th moment → particle density (n) • higher moments are <velocity> & temperature, • pressure tensor, heat flux tensor • opacity/transmissionis the first probe • Transport properties (e.g. diffusion, viscosity) • Screening • Collective Effects • hydrodynamic expansion velocity, shock propagation • → density correlations inside plasma • Radiation • bremsstrahlung, blackbody, collisional and recombination • Plasma oscillations, instabilities

7. schematic view of jet production hadrons leading particle q q hadrons leading particle transmission of probes which interact with plasma EM plasma: x-ray transmission for QGP: fast g and quarks probes must carry color charge

8. I. Vitev calculate using an opacity expansion answer: L/mfp ~ 3.5 (model dependent) r≥ 1000 gluons/unit y d+Au Au+Au high parton density from jet quenching interaction of radiated & plasma gluons enhances the amount of radiation

9. Jet tomography at RHIC II to go beyond <r> • jet quenching vs. system size, energy • → parton & energy density for EOS • → vary pT to probe medium coupling, • early development of system • golden channel: g-jet correlations • g fixes jet energy • flavor-tagged jets to sort out g vs. q energy loss • need detector upgrades (calorimeter coverage, DAQ) • must have RHIC II’s increased luminosity for: • statistics for clean g-jet & multi-hadron correlations • system scan in a finite time cross section is small, so rate is low

10. transport in plasmas ↔ collisions • transport of particles → diffusion • transport of energy by particles → thermal conductivity • transport of momentum by particles → viscosity • transport of charge by particles → electrical conductivity • is transport of color charge an analogous question for us?

11. radiation vs. collisions? consider leptons in matter • electrons stop in matter • g (bremsstrahlung) radiation • muons have long range • radiation is suppressed by the large mass • dominant energy loss mechanism is via collisions • implication • use heavy quarks as second kind of probe • collisions should be important for c, b quarks is light quark energy loss radiation dominated? EM plasmas → no radiation: blackbody, bremsstrahlung, collisional, recombination

12. evidence for both radiation & collisions RAA for heavy mesons via e± from semileptonic decays Wicks, et al. nucl-th/0512076

13. PHENIX preliminary diffusion = transport of particles by collisions D = 1/3 <v> lmfp = <v>/ 3rs D  collision time →relaxation time Moore & Teaney PRC71, 064904, ‘05 D ~ 3/(2pT) is small! → strong interaction of c quarks larger D →less charm e loss fewer collisions, smaller v2

14. burning questions • what is the role of B decays? • need RHIC II luminosity & upgrades to measure • direct probe of extent, timescale of thermalization? • RHIC II will yield • statistics for v2, pT reach • allow scan of systems with exclusive decay channels • relative abundance of charmed hadron states • Another important transport property is viscosity • found to be (very) small at RHIC

15. Screening: Debye Length • distance over which the influence of an individual charged particle is felt by the other particles in the plasma • charged particles arrange themselves so as to effectively shield any electrostatic fields within a distance of order lD • lD = e0kT • ------- • nee2 • Debye sphere = sphere with radius lD • number electrons inside Debye sphere is typically large • ND= N/VD= rVD VD= 4/3 plD3 1/2 in strongly coupled plasmas it’s  1

16. Debye screening in QCD: a tricky concept • in leading order QCD (O. Philipsen, hep-ph/0010327) • vv

17. don’t give up! ask lattice QCD Karsch, et al. running coupling coupling drops off for r > 0.3-0.4 fm

18. screening masses from gluon propagator Screening mass, mD, defines inverse length scale Inside this distance, an equilibrated plasma is sensitive to insertion of a static source Outside it’s not. Nakamura, Saito & Sakai, hep-lat/0311024 T dependence of electric & magnetic screening masses Quenched lattice study of gluon propagator figure shows: mD,m= 3Tc, mD,e= 6Tc at 2Tc lD ~ 0.4 & 0.2 fm magnetic screening mass is non-zero not very gauge-dependent, but DOES grow w/ lattice size (long range is important)

19. Karsch, Kharzeev, Satz, hep-ph/0512239 40% of J/y from c and y’ decays they are screened but direct J/y not? Probe experimentally: onium spectroscopy

20. Need RHIC II luminosity to sort out! yields in PHENIX from Tony Frawley

21. STAR yield estimates from Tony Frawley

22. collective effects a basic feature distinguishing plasmas from ordinary matter • simultaneous interaction of each charged particle with a considerable number of others • due to long range of the forces • EM plasma: charge-charge & charge-neutral interactions • charge-neutral dominates in weakly ionized plasmas • neutrals interact via distortion of e cloud by charges • very sensitive to coupling, viscosity… • magnetic fields generated by moving charges give rise to magnetic interactions

23. strong elliptic flow; scales w/ number of quarks

24. sort out via3D hydro + measure v2 vs. v3, v4 scan in system size & energy c, W, X, f flows to separate late stage dissipation from early viscous effects  RHIC II luminosity Kolb, et al data + hydrodynamics → very low viscosity Ideal hydrodynamics (h/S =0) enough to conclude viscosity=0? Deviations → viscous effects? note: softer than hadronic EOS!! RHIC viscosity has drawn great interest from other fields including string theorists, who conjecture a lower bound h/S ≥ (h/4p)

25. minimum h at phase boundary? seen in strongly coupled dusty plasma MD: solve the equations of motion for massive particles subject to (screened) interaction potential follow evolution of particle distribution function (&correlations) solve coupled diff.eq’s over nearby space density-density correlations →h B. Liu and J. Goree, cond-mat/0502009 minimum arises because kinetic part of h decreases with G & potential part increases

26. STAR Preliminary (1/Ntrig)dN/d(Df) M.Miller, QM04 PHENIX dN/d(Df) 0 p/2 p p/2 p Df challenge: can a jet excite a density wave in the plasma? g radiates energy kick particles in the plasma accelerate them along the jet non-equilibrium process

27. generally a phenomenon in crystals but not liquids

28. other key measurements at RHIC II • Temperature of plasma • Medium modification • of hadrons at later stage • g elliptic flow & HBT • map baryon & multi-strange • hadron production • poke at hadronization mechanism • & probe 2q correlations in the medium all have large backgrounds require RHIC II luminosity & detector upgrades to reject background & probe as a function of e, m

29. wave functions • of proton • only 20-30% of spin carried by quarks • polarized pp tests role of g & also q orbital motion • RHIC II luminosity allows: • precision DG(x) • flavor dependence: sea polarized opposite to valence? • disentangle  orbital motion (Sivers effect) from  spin alignment (transversity) via single  spin asymmetries • of heavy nucleus • high gluon density → saturated, highly coherent matter • explains low dN/dh & forward hadrons in d+Au • RHIC II luminosity allows: • asymmetric collisions at forward rapidity • search for monojets in d+Au (rare process!) • important ingredient to thermalization process!!

30. RHIC II will get us • from “oh wow!” • we have found a surprising new form of matter • to “aha!” • here is how it works • how QGP relates to and drives progress in other fields

31. backup slides

32. QGP energy density • > 1 GeV/fm3 i.e. > 1030 J/cm3 Energy density of matter high energy density: e > 1011 J/m3 P > 1 Mbar I > 3 X 1015W/cm2 Fields > 500 Tesla

33. specific channels • map transversity to get at nucleon’s tensor charge • Sivers function • probes correlation among p spin & parton pT inside • arises from rescattering of struck parton in color field of nucleon remnant • experimentally, look at  spin asymmetry for DY • needs increased calorimeter coverage & luminosity

34. plasma properties known, so far Extract from models, constrained by data

35. RAA baryon puzzle… baryons enhanced for pT < 5 GeV/c

36. PHENIX preliminary PHENIX preliminary 0-5%

37. use this technique to measure viscosity melt crystal with laser light induce a shear flow (laminar) image the dust to get velocity study: spatial profiles vx(y) moments, fluctuations → T(x,y) curvature of velocity profile → drag forces viscous transport of drag in  direction from laser compare to viscous hydro. extract h/r shear viscosity/mass density PE vs. KE competition governs coupling & phase of matter Csernai,Kapusta,McLerran nucl-th/0604032

38. look at radiated & “probe” particles • as a function of transverse momentum • pT = p sin q (with respect to beam direction) • 90° is where the action is (max T, r) • midway between the two beams! • pT < 1.5 GeV/c • “thermal” particles • radiated from bulk of the medium • internal plasma probes • pT > 3 GeV/c • jets (hard scattered q or g) • heavy quarks, direct photons • produced early→“external” probe

39. Hatsuda, et al. Lattice QCD shows qq resonant states at T > Tc, also implying high interaction cross sections Fast equilibration, highopacity (even for charm): how? Molnar multiple collisions using free q,g scattering cross sections doesn’t work! need s x50 in the medium

41. Plasma Coulomb coupling parameter G • ratio of mean potential energy to mean kinetic energy • a = interparticle distance • e = charge • T = temperature • typically a small number in a normal, fully shielded plasma • G = 1/(number particles in Debye sphere) • when G > 1 have a strongly coupled, or non-Debye plasma • many-body spatial correlations exist • behave like liquids, or even crystals when G > 150 • lD < a

42. estimate G using this use l=0.2 fm from electric screening mass e=15 GeV/fm3 from hydro initial conditions constrained by v2 density from dE/dx constrained by RAA put them together: get 0.5 GeV inside Debye sphere FEW particles! ~1 →G ~ 1  quark gluon plasma should be a strongly coupled plasma • As in warm, dense plasma at lower (but still high) T • dusty plasmas, cold atom systems • such EM plasmas are known to behave as liquids!