Big Bang in the Laboratory? A droplet of Quark Gluon Plasma

1. Big Bang in the Laboratory? A droplet of Quark Gluon Plasma Barbara Jacak Stony Brook University

2. outline • Energy densities characteristic of the early universe • What is quark gluon plasma & why do we expect it? • Nuclear Physics at very high energy • Experiments at the Relativistic Heavy Ion Collider • How we probe the hot, dense matter • First glimpse of the matter’s properties • Relation to other plasmas • Conclusions & (some interesting) open questions

3. Quark-GluonPlasma?? Too hot for quarks to bind!!! Standard Model (N/P) Physics Too hot for nuclei to bind Nuclear/Particle (N/P) Physics HadronGas Nucleosynthesis builds nuclei up to He Nuclear Force…Nuclear Physics E/M Plasma Universe too hot for electrons to bind E-M…Atomic (Plasma) Physics Today’s Cold Universe Gravity…Newtonian/General Relativity SolidLiquidGas Evolution of the Universe

4. Quarks, gluons and hadrons • 6 quarks: 2 light (up,down), 1 sort of light (strange), 2 heavy (charm,bottom), 1very heavy (top) • Besides flavor, also have color quantum number • In normal life: quarks are bound into hadrons Baryons (e.g. n, p) have 3 Mesons (e.g. p, K, f) have 2 (1 quark + 1 anti-quark) • Plasma: • Ionized gas, but dense enough • that the charges of nearby • neighbors shield one another (the quarks & gluons aren’t bound but do interfere with one another)

5. QGP energy density • > 1 GeV/fm3 i.e. > 1030 J/cm3 Energy Density in the Universe high energy density: e > 1011 J/m3 P > 1 Mbar I > 3 X 1015W/cm2 Fields > 500 Tesla

6. + +… Short distance: asymptotic freedom phase transition to quark gluon plasma • Colored quarks interact by exchange of gluons (also have color) • Quantum Chromo Dynamics (QCD) Field theory of the strong interaction Parallels Quantum Electrodynamics QED (EM interactions: exchanged photons electrically uncharged) Color charge of gluons  gluons interact among themselves • theory is non-abelian • curious properties at large distance: • confinement of quarks in hadrons

7. Karsch, Laermann, Peikert ‘99 e/T4 T/Tc Tc ~ 170 ± 10 MeV (1012 °K) e ~ 3 GeV/fm3 QCD – lattice gauge theory Solve problem of summing over all gluon interactions by calculating on a (big) lattice

8. Explore in the lab: collide BIG ions at v ~ c • Aim for T  170 MeV; e > 3 GeV/fm3 • Characterize the hot, dense medium • What’s the density, temperature, radiation rate, collision frequency, screening length, conductivity? • Evidence for phase transition to quark gluon plasma? • does medium behave as a plasma? pressure vs. energy? • Probes • passive (radiation) • those created in the collision (“external”)

9. RHIC at Brookhaven National Laboratory Collide Au + Au ions for maximum volume s = 200 GeV/nucleon pair, p+p and d+A to compare

10. STAR 4 complementary experiments

11. The Scope of the Tools (!) STAR specialty: large acceptance measurement of hadrons PHENIX specialty: rare probes, leptons, and photons

12. Uncovering nature’s secrets is not easy! Large collaborations PHENIX has ~500 people many countries! “small” experiments have > 50 people! Write ~ 100 Mb/sec to tape • Use connected computing all around the world! • transfer data over the internet, tape • centrally located software libraries • meetings span 3 continents • everyone phones in, post slides on the web • circulate agendas, questions by email Use Grid computing

13. Hard scattered q,g (short wavelength) probes of plasma formed p, K, p, n, f, L, D, X, W, d, g, g* e+e-, m+m- Hadrons reflect (thermal) properties when inelastic collisions stop Real and virtual photon radiation probing early stage of heavy ion collision e, pressure builds up total lifetime of the system ~ 10 fm/c or ~ 3 x 10-23 seconds

14. So what happens? • Lots of information collected over past 4 years • I’ll establish it’s fair to look for new physics, • and report only a few important results • Focus on “external” probes • No laser with sufficiently short wavelength! • Use probes made in the first step of the collision • Rate and spectrum calculable with (perturbative) QCD • look for effects of the medium • Start by benchmarking the probe!

15. p-p PRL 91 (2003) 241803 Good agreement with NLO pQCD Parton distribution functions Fragmentation functions Start simple p+p collisions QCD works for high p transfer processes!  Have a handle on initial NN interactions by scattering of q, g inside N We also need: p0 These are measured, so known

16. Now ask: is energy density high enough? We measure the particles coming out, so add up their energy

17. Energy  to beam direction per unit velocity || to beam pR2 2ct0 energy density = E/volume Colliding system expands: E • e 5.5 GeV/fm3 (200 GeV Au+Au) well above predicted transition! value is lower limit: longitudinal expansion rate, formation time overestimated

18. schematic view of jet production hadrons leading particle q q hadrons leading particle AA AA AA nucleon-nucleon cross section <Nbinary>/sinelp+p “external” probes of the medium Hard scattering of q,g early. Observe fast leading particles, back-back correlations Before creating hadron jets, scattered quarks induced to lose energy (~ GeV/fm) by the colored medium -> jet quenching

19. Au-Au s = 200 GeV: high pT suppressed! PRL91, 072301(2003)

20. near side away side Medium is opaque! STAR peripheral central look for the jet on the other side STAR PRL 90, 082302 (2003) Peripheral Au + Au Central Au + Au

21. Suppression: a final state effect? Hot, dense medium causes Such a medium is absent in d+Au collisions! But Au provides all initial state effects of q, g wavefunction inside a Au nucleus d+Au is the “control” experiment

22. Centrality Dependence Au + Au Experiment d + Au Control PHENIX preliminary • Dramatically different and opposite centrality evolution of AuAu experiment from dAu control. • Jet Suppression is clearly a final state effect.

23. leading particle suppressed hadrons Pedestal&flow subtracted q q So this is the right picture for Au+Au ? Are back-to-back jets there in d+Au? Yes!

24. Almond shape overlap region in coordinate space Collective motion? Pressure: a barometer called “elliptic flow” Origin: spatial anisotropy of the system when created, followed by multiple scattering of particles in the evolving system spatial anisotropy  momentum anisotropy v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane

25. The data show Particle emission really is azimuthally anisotropic Magnitude of the anisotropy grows with beam energy, then flattens c.m. beam energy

26. Hydro. Calculations Huovinen, P. Kolb, U. Heinz STAR v2 reproduced by hydrodynamics PRL 86 (2001) 402 central • see a large pressure buildup • anisotropy  happens fast while system is deformed • success of hydrodynamics early equilibration ! • ~ 0.6 fm/c

27. Kolb, et al STAR Collective effect probes equation of state Hydrodynamics can reproduce magnitude of elliptic flow for p, p. BUT correct mass dependence requires softer than hadronic EOS!! NB: these calculations have viscosity = 0 medium behaves as an ideal liquid

28. Elliptic flow scales as number of quarks • v2 scales ~ with # of quarks! • evidence that quarks are the particles when the pressure is built up

29. equilibrated final state, including s quarks Hadron yields in agreement with Grand Canonical ensemble T(chemical freeze-out) ~ 175 MeV (~ Tc) (multi)strange hadrons enhanced over p+p, but QGP hypothesis not unique explanation

30. So, what do E loss & collectivity tell us? • Medium is “sticky” or opaque to colored probes • Thermalization must be very fast (< 1fm/c) • Constrain hydrodynamic, energy loss models with data:

31. Lattice QCD shows qq resonant states at T > Tc, also implying high interaction cross sections Is s enough for fast equilibration & large v2 ? Parton cascade using free q,g scattering cross sections underpredicts pressure must increase x50

32. What is going on? • The objects colliding are not baryons and mesons • The objects colliding also do not seem to be quarks and gluons totally free of the influence of their neighbors • Quarks and gluons are interacting, but are not locally neutral like the baryons & mesons

33. Plasma coupling parameter? • Very high gluon density! • estimate G = <PE>/<KE> • using QCD coupling strength • <PE>=g2/d d ~1/(41/3T) • <KE> ~ 3T • g2 ~ 4-6 (value runs with T) • G ~ g2 (41/3T)/ 3T  so plasma parameter G ~ 3 • NB: such plasmas known to behave as a liquid! • May have bound q,g states, but not color neutral • So the quark gluon plasma is a strongly coupled plasma • As in warm, dense plasma at lower (but still high) T • But strong interaction rather than electromagnetic

34. Other strongly coupled plasmas • Inside white dwarf and neutron stars (n star core may even contain QGP) • In ionized gases subjected to very high pressures or magnetic fields • Dusty plasmas in interplanetary space & planetary rings • Solids blasted by a laser • We would like to know: • How do these plasmas transport energy? • How quickly can they equilibrate? • What is their viscosity? G >10 can even be crystalline! • How much are the charges screened? • Is there evidence of plasma instabilities at RHIC? • Can we detect waves in this new kind of plasma? novel plasma of strong interaction

35. E. Shuryak

36. How about the screening length? • J/Y • Test confinement: • do bound c + c survive? • or does QGP screening kill them? • Suppression was reported in lower • energy heavy ion collisions at CERN Need (a lot) more statistics (currently being analyzed) But can take a first look…

37. 0-20% most central Ncoll=779 40-90% most central Ncoll=45 20-40% most central Ncoll=296 Lattice predictions for heavy quarks Color screening? These data still inconclusive

38. conclusions Evidence that RHIC creates a strongly coupled, opaque plasma energy density & equation of state not hadronic! still is debate in community about the standard of proof • With aid of hydrodynamics, l-QCD and p-QCD models: • e ~ 15 GeV/fm3 • dNgluon/dy ~ 1000 • sint large for T < 2-3 Tc • Are poised to characterize this new kind of plasma • T, radiation rate, conductivity, collision frequency • More interdisciplinary than we first thought! • will have a workshop with Plasma community in December • also close to Particle & Condensed Matter Physics, Astrophysics, Mathematical modeling, Large-scale computing…

39. r/ ggg d + Au collisions cent/periph. (~RAA) Saturation of gluons in initial state(colored glass condensate) Mueller, McLerran, Kharzeev, … Wavefunction of low x (very soft) gluons overlap and the self-coupling gluons fuse. Saturation at higher x at RHIC vs. HERA due to nuclear size  suppressed jet cross section; no back-back pairs

40. Open charm: baseline is p+p collisions PHENIX PRELIMINARY Measure charm s via semi-leptonic decay to e+ & e- p0, h, photon conversions are measured and subtracted fit p+p data to get the baseline for d+Au and Au+Au.

41. Charm production s scales as Ncoll! The yellow band represents the set of alpha values consistent with the data at the 90% Confidence Level.

42. No large suppression as for light quarks! PHENIX PRELIMINARY Curves are the p+p fit, scaled by the number of binary collisions

43. Evidence for equilibrated final hadronic state BRAHMS • Simple quark counting: K-/K+ = exp(2ms/T)exp(-2mq/T) = exp(2ms/T)(pbar/p)1/3 = (pbar/p)1/3 • local strangeness conservation K-/K+=(pbar/p)a a = 0.24±0.02 BRAHMS a = 0.20±0.01 for SPS • Good agreement with statistical-thermal model of Beccatini et al. (PRC64 2001) w/T=170 MeV From y=0 to 3 At y=0 PRL 90 102301 Mar. 2003

44. Implications of the results for QGP • Ample evidence for equilibration • initial dN(gluon)/dy ~ 1000, energy density ~ 15 GeV/fm3, energy loss ~ 7-10 GeV/fm • Very rapid, large pressure build up requires • parton interaction cross sections 50x perturbative s

45. How to get 50 times pQCD s? spectral function • Lattice indicates that hadrons don’t all melt at Tc! • hc bound at 1.5 Tc Asakawa & Hatsuda, PRL92, 012001 (2004) • charmonium bound states up to ~ 1.7 Tc Karsch; Asakawa&Hatsuda • p, s survive as resonances Schaefer & Shuryak, PLB 356 , 147(1995) • q,g have thermal masses at high T. as runs up at T>Tc? (Shuryak and Zahed) • would cause strong rescattering qq  meson

46. Implications of the results for QGP • Ample evidence for equilibration • v2 & jet quenching measurements constrain initial gluon density, energy density, and energy loss • parton interaction cross sections 50x perturbative s • parton correlations at T>Tc • complicates cc bound states as deconfinement probes! • Hadronization by coalescence of thermal,flowing quarks • v2 & baryon abundances point to quark recombination as hadronization mechanism • Jet data imply must also include recombination between quarks fromjets and the thermalized medium •  medium modifies jet fragmentation!

47. early universe 250 RHIC 200 quark-gluon plasma 150 SPS Lattice QCD AGS deconfinement chiral restauration thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] Locate RHIC on phase diagram From fit of yields vs. mass (grand canonical ensemble): Tch = 176 MeV mB = 41 MeV These are the conditions when hadrons stop interacting T Observed particles “freeze out” at/near the deconfinement boundary!

48. Do see Cronin effect! (h++h-)/2 “Cronin” enhancement more pronounced in the charged hadron measurement Possibly larger effect in protons at mid pT Implication of RdAu? RHIC at too high x for gluon saturation… p0

49. No CGC signal at mid-rapidity So, perhaps Rda G-sat. Rda pQCD >2 BFKL, DGLAP Xc(A) RHIC Pt (GeV/c) Pt (GeV/c) Log Q2 How about Color Glass Condensate? Central: Enhanced not suppressed PHENIX preliminary y=0 Peripheral d+Au (like p+p)

50. d Au PhenixPreliminary But at forward rapidity reach smaller x y = 3.2 in deuteron direction  x  10-3 in Au nucleus Strong shadowing, maybe even saturation?