Experiments at RHIC: Exciting Discoveries & Future Plans

1. Experiments at RHIC:Exciting Discoveries & Future Plans Barbara Jacak Stony Brook University June 20, 2006

2. outline • introduction • plasmas and strong coupling • collective effects • hydrodynamics and viscosity • transmission of probes by the quark-gluon plasma • heavy quark probes • diffusion color screening • Color Glass Condensate (discussed by Dima) • Plasma Physics of the Quark Gluon Plasma at RHIC II

3. Karsch, Laermann, Peikert ‘99 ~15% from ideal gas of weakly interacting quarks & gluons e/T4 We now know this leaves room for a big deviation from weak coupling T/Tc Tc ~ 170 ± 10 MeV (1012 °K) e ~ 3 GeV/fm3 required conditions (per lattice)

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. 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 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

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

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

8. Implications of lD ~ 0.3 fm • can use to estimate Coupling parameter, G • G = <PE>/<KE> but also G = 1/ND • for lD = 0.3fm and e = 15 GeV/fm3 • VD = 4/3 plD3 = 0.113 fm3 • ED = 1.7 GeV • to convert to number of particles, use gT or g2T • for T ~ 2Tc and g2 = 4 • get ND = 1.2 – 2.5 • G ~ 1 • NB: for G ~ 1 • plasma is NOT fully screened – it’s strongly coupled! • other strongly coupled plasmas behave as liquids, even crystals for G≥ 150 • dusty plasmas, cold atoms+ions , warm dense matter

9. to study experimentally: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

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

11. STAR 4 complementary experiments

12. 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 (electromagnetic) forces • magnetic fields generated by moving charges give rise to magnetic interactions

13. z y x Almond shape overlap region in coordinate space search for collectivity in QGPuse “internal” probes – emitted particles momentum space dN/df ~ 1 + 2 v2(pT) cos (2f) + … “elliptic flow”

14. Kolb, et al Hydrodynamics reproduces elliptic flow of q-q and 3q states Mass dependence requires softer than hadronic EOS!! NB: these calculations have viscosity ~ 0 “perfect” liquid (D. Teaney, PRC68, 2003) v2 is large & reproduced by hydrodynamics • large pressure buildup • anisotropy  happens fast • fast equilibration!

15. Greco, Ko, Levai: PRC 68 (2003)034904 Elliptic flow scales with number of quarks implication: quarks are the relevant degrees of freedom when the pressure is built up. Hadronization: quark coalescence

16. D. Morrison, SQM’06 at high pT v2 reflects opacity of medium approximately expected level from jet quenching

17. 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

18. nuclear modification factor • photons escape plasma • pions and other hadrons: strong interaction, absorbed

19. A, Majumder (Quark Matter 05) Dainese, talk at PANIC05 AMY flat RAA via radiative energy loss only

20. RAA wrt reaction plane – more discriminating Energy loss depends on the path-length, expansion, collisions(?)

21. Pedestal&flow subtracted dihadrons: away side suppressed (low pT)

22. some away side particles “reappear” at higher pT STAR nucl-ex/0604018 pT trigger > 8 GeV/c

23. away side yield: some jets escape, some eaten STAR nucl-ex/0604018 Note similarity of away side jet fragmentation. Only yield changes

24. STAR Preliminary (1/Ntrig)dN/d(Df) M.Miller, QM04 PHENIX dN/d(Df) 0 p/2 p p/2 p Df CAN WE DO THIS????? =+/-1.23=1.91,4.37 → cs ~ 0.33 (√0.33 in QGP, 0.2 in hadron gas) how does plasma respond to deposited energy? E. Shuryak: g radiates energy kick particles in the plasma, accelerate them in jet direction: a sound wave

25. PHENIX preliminary PHENIX preliminary not an experi-mental artefact! J. Jia

26. generally a phenomenon in crystals but not liquids

27. d+Au Δ2 Au+Au Central 0-12% Triggered Δ1 Δ1 3 particle correlations support cone-like structure J. Ulery, HP06

28. charm also flows thermalization with the light quarks? not so easy! to further test interaction: heavy quarks ~ same E loss as u,d quarks  energy loss not all radiative need collisions!

29. Inclusion of collisional energy loss leads to better agreement with single electron data, even for dNg/dy=1000. NB: effect of collisional energy loss for light quarks… RAA of e± from heavy flavors was a shock Wicks, Horowitz, Djordjevic, & Gyulassy, nucl-th/0512076

30. 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

31. aim to measure the screening length J/Y (bound state of c and cbar quarks) Tests screening & confinement: • do bound c + c survive the medium? • or does QGP screening kill them? Look at RAA for J/y different bound states probe different lengths

32. At RHIC: J/ymm muon arm 1.2 < |y| < 2.2 measured/expected dAu mm 200 GeV/c AuAu mm 200 GeV/c CuCu mm 200 GeV/c

33. At RHIC: J/ymm muon arm 1.2 < |y| < 2.2 J/yee Central arm -0.35 < y < 0.35 dAu mm 200 GeV/c AuAu mm 200 GeV/c CuCu mm 200 GeV/c AuAu ee 200 GeV/c CuCu ee 200 GeV/c

34. At RHIC: J/ymm muon arm 1.2 < |y| < 2.2 J/yee Central arm -0.35 < y < 0.35 ! Factor ~3 suppression in central events dAu mm 200 GeV/c AuAu mm 200 GeV/c CuCu mm 200 GeV/c AuAu ee 200 GeV/c CuCu ee 200 GeV/c CuCu mm 62 GeV/c

35. RAA vs Npart: PHENIX and NA50 • NA50 data normalized at NA50 p+p point. • Suppression similar in the two experiments, although the collision energy is 10 times higher (200GeV in PHENIX & 17GeV in NA50)

36. What suppression should we expect? Models that were successful in describing SPS data fail to describe data at RHIC - but lattice QCD says bound states until ~2Tc -

37. direct regeneration Regeneration  Narrowing of pT and y? Thews et al. • pT broadening in between Thews direct & in-medium formation: some regeneration • Recombination → narrower rapidity distribution with increasing Npart • BUT: From p+p to central Au+Au : no significant change in y distribution. Recombined only No Recombination slide from T. Ullrich, HP06

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

39. Plasma Physics of the QGP with RHIC II plasma 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, plasma waves • → density correlations inside plasma • Radiation • bremsstrahlung, blackbody, collisional and recombination • Plasma oscillations, instabilities

40. 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

41. next step in transmission study: jet tomography small s, low rate • 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 luminosityx10 for: • statistics for clean g-jet & multi-hadron correlations • system scan in a finite time • tool of choice to study medium response/conductivity

42. measure D & B decays; onium spectroscopy inner trackers for PHENIX and STAR + RHIC II luminosity! PHENIX STAR

43. need high luminosity to scan energy & system • pin down viscosity (and the collision dynamics) • sort out via 3D hydro + • measure v2 vs. v3, v4 • c, W, X, f flows to separate late stage dissipation from early viscous effects • thermalization • plasma temperature via radiated g, g* • c, W, X, f flows • can we identify signals of early plasma instability? • probe 2q correlations via baryon production? • direct search for density correlations poses a • challenge to experiment & theory both!

44. conclusion - discoveries • The matter created shows collective flows • developed early, with quarks/gluons the likely d.o.f. • magnitude implies very low viscosity • QGP behaves as a liquid • similar to other strongly coupled plasmas! • Very opaque to color charged probes • even charm quarks lose energy and flow! • another result of strong coupling • J/ suppressed, but only partially • perhaps screening + recombination from thermal bath? • or sequential melting of c and ` • Evidence of CGC initial state • The matter behaves as expected for a plasma!

45. conclusion – future plans • figure out the plasma physics of this new kind of matter: • temperature • transport properties • collective excitations • expansion dynamics • density waves • instabilities? • screening length • need • detector upgrades (planning, construction underway) • high luminosity of RHIC II (x10 via electron cooling) • low s probes, scan properties with system & energy

46. 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

47. backup slides

48. conclusions • the matter formed at RHIC is a “perfect” fluid • shows collective flows with small viscosity • huge interaction cross sections, very opaque • multiple collisions affect even heavy charm quarks • color is partially, but not completely, screened • this is like other strongly coupled plasmas • as it should be → it is a plasma! • neutrality scale > interparticle distance • How does this super high energy density plasma work? • □ map properties of the new stuff at RHIC • how does the plasma transport the “lost” energy? • radiation rate? • initial temperature achieved? (theory says ~380 MeV) • □ collide Pb+Pb at the LHC for higher Tinitial • reach ~ 800 MeV: is coupling strong or weak?

49. 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

50. PHENIX preliminary PHENIX preliminary not an experi-mental artefact,part I J. Jia