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Poking at the Quark Gluon Plasma with Jets and Heavy Quarks

Explore the properties of quark-gluon plasma by studying interactions with jets and heavy quarks. Understand the behavior of this exotic state of matter and its effects on particle collisions.

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Poking at the Quark Gluon Plasma with Jets and Heavy Quarks

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  1. Poking at the Quark Gluon Plasma with Jets and Heavy Quarks Barbara Jacak Stony Brook UIUC Seminar March 5, 2008

  2. What’s this stuff? let’s poke it with a stick! follow in the footsteps of Rutherford and friends experimenting with radioactivity… Scattered partons propagate: • fast quarks & gluons traverse the interesting stuff • radiate gluons • interact with QGP partons Fragment into jets • usually described by phenomenological fragmentation function • in/outside the medium

  3. lattice QCD F. Karsch properties of matter ^ QCD • thermodynamic (equilibrium) • T, P, r • EOS (relate T,P,V, e) • vsound, static screening length • transport properties* • particle number, energy, momentum, charge • diffusion sound viscosity conductivity • * measuring these is new for nuclear/particle physics!

  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 • gluons self-interacting, number (not fixed)  T

  5. X-ray tomography: to get temporal and spatial evolution of plasma mode activity, use 10 soft X-ray cameras with 20 channels each, at 70 kHz max.  typical plasma diagnostics

  6. e, pressure builds up Hard scattered q,g (short wavelength) probes of plasma formed p, K, p, n, f, L, D, X, W, d, Hadrons reflect (thermal) properties when inelastic collisions stop (chemical freeze-out). color-screened QGP thermal radiation (g, g* e+e-, m+m-) heavy ion collision diagnostics time not possible to measure as a function of time nature integrates over the entire collision history

  7. study plasma by 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) • pL midway between the two beams: midrapidity • pT < 1.5 GeV/c • “thermal” particles • radiated from bulk of the medium • pT > 3 GeV/c • jets (hard scattered q or g) • heavy quarks, direct photons • describe by perturbative QCD • produced early→“external” probe

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

  9. Experimenter’s Tools STAR specialty: large acceptance measurement of hadrons PHENIX specialty: rare probes, leptons, and photons

  10. a bit of geometry, terminology • baseline for heavy ion collisions: p+p collisions • peripheral collisions (large impact parameter) are like a handful of p+p collisions • central (small impact parameter) collisions produce largest plasma volume, temperature, lifetime • report centrality as fraction of total A+A cross section • 0-5% = very central peripheral: few participant nucleons (small Npart) few NN collisions (Ncoll) central: large Npart & Ncoll Ncoll near 1000 in ~ head-on Au+Au

  11. p-p PRL 91 (2003) 241803 Good agreement with pQCD head-on Au+Au Ncoll = 975  94 The matter is opaque! jets are quenched p0

  12. how opaque is hot QCD matter? colored objects lose energy, photons don’t

  13. energy loss by induced gluon radiation I. Vitev d+Au interaction of radiated gluons with gluons in the plasma greatly enhances the amount of radiation Au+Au opacity expansion analysis shows <medium length traversed>/mean free path ~ 3.5 → r~ 1400 gluons/unit rapidity

  14. energy transport

  15. constrain with data data & fit: arXiv:0801.1665 PQM model: C. Loizides Eur.Phys.J. C49 (2007) 339 ^ • extract transport parameter q • from data, get ~ 13 GeV2/fm • but pQCD favors ~1 (Baier, et al)

  16. momentum exchange: complicated process The medium is dense and opaque! Quantifying energy deposit ..ongoing Different models include radiation, w/ or w/o collisions some/no transfer medium→probe different level of detail describing collisiongeometry different handling of fluctuations different description of the expansion dynamics

  17. Central Au + Au same jet opposing jet collective flow in underlying event medium transport of deposited energy? • study using hadron pairs • high pT trigger to tag hard scattering • second particle to probe the medium

  18. on away side: same distribution of particles as in p+p but ~5 times fewer! expected for opaque medium X at high momentum, jets punch through central collisions Phys.Rev.Lett. 97 (2006) 162301 STAR

  19. Direct Photon-HadronDf Correlations in p+p toward jet tomography: Compton scattering g tags q energy 12-15 GeV “monoenergetic jet” q+g → q+g p0 - h gdir - h • right mechanism • same jet partners are absent • away jet shows similar modification • next step: quantify energy/momentum flow 1/Ntrig dN/dDf (A.U.) Df [rad] M.A. Nguyen Quark Matter 2008 Quark Matter 2008 2/8/2008 19

  20. RHIC II AuAu 20 nb-1 Where we need to go • g tags q energy • >12 GeV • “monoenergetic” jets • all we need is: • more events • bigger detector • coverage • all those near-by curves • very different • with no medium • ALL use weak coupling! g-jet

  21. 3<pt,trigger<4 GeV pt,assoc.>2 GeV Au+Au 0-10% preliminary STAR lower pT partners look funny! medium responds to the “lost” energy central peripheral 1 < pT,a < 2.5 < pT,t <4 GeV/c

  22. jets shock the medium p+p central Au+Au

  23. strong coupling: ask AdS/CFT answer: yes it does! mach cone wake Gubser,Pufu,Yarom PRL100, 012301’08 Chesler & Yaffe, 0706.0368(hep-th) lost energy excites a sound (density) wave? if shoulder is sound wave… LOCATION at =+/-1.23=1.91,4.37 → speed of sound cosfm=cs~0.35-0.4(cs2=0.33 in QGP,~0.19 in hadron gas) relative excitation of sound and diffusion wake in intense study data →sound mode large

  24. e± X D Au Au D p K Diffusion of heavy quarks traversing QGP • How do they interact? • Prediction: lower energy loss than light quarks • large quark mass reduces phase space for radiated gluons • Measure via semi-leptonic decays • of mesons containing • charm or bottom quarks

  25. c,b decays via single electron spectrum compare data to “cocktail” of hadronic decays

  26. PRELIMINARY minimum-bias Rapp & van Hees, PRC 71, 034907 (2005) Heavy quarks do flow!! Use to probe transport properties of QGP! Run-7 Run-4 sufficient interaction to equilibrate?? • Measure correlation of e±with the light hadrons • Ask whether they flow along. • NB: rate of equilibration gives information on the viscosity of the liquid!

  27. Wicks et al., NPA 784(2007)426 heavy quarks lose energy too e± from heavy quark decay cannot be dominantly by bremsstrahlung (gluon radiation) plasmas have collisions among constituents! including it helps larger than expected scattering s→ stronger coupling

  28. heavy quark transport: diffusion & viscosity • diffusion = brownian motion of particles definition: flux density of particles J = -D grad n • integrating over forward hemisphere: D = diffusivity = 1/3 <v> l so D = <v>/ 3ns D  collision time, determines relaxation time Langevin: equation of motion for diffusion thru a medium drag force  random force  <DpT2>/unit time  D* particle concentration l = mean free path note: viscosity is ability to transport momentum h = 1/3 r <v> l so D = h/r ~ h/S → measure D get h! * G. Moore and D. Teaney, hep-ph/0412346

  29. confronting mechanisms with data PRL98, 172301(2007) Radiative energy loss alone: fails to reproduce v2 Heavy quark transport model (i.e. diffusion) shows better agreement with RAA and v2 Though agreement with data is so-so, slow relaxation ruled out by v2 D ~ 4-6/(2pT) for charm h/S = (1.3 – 2.0)/ 4p

  30. R. Lacey et al.: PRL 98:092301, 2007 S. Gavin and M. Abdel-Aziz: PRL 97:162302, 2006 H.-J. Drescher et al.: arXiv:0704.3553 pTfluctuations STAR v2 PHOBOS v2 PHENIX & STAR conjectured quantum limit Comparison with other estimates • estimates of h/s based on flow and fluctuation data • indicate small value as well • close to conjectured limit • significantly below h/s of helium (4ph/s ~ 9)

  31. PRL 98, 172301 (2007) e± from heavy flavor b quark contribution to single electrons becomes significant. do they also lose energy? What about b quarks?

  32. Hard probes tell us: • Energy loss in the plasma is large. • and/or as ~ 0.27. • What quantity DO we measure? Eloss mechanism? • Deposited energy shocks the medium. Mach cones? • cs ~ (0.35 – 0.4) c (closer to hadron gas than QGP) • expected diffusion wake AWOL (baryon enhancement?) • Medium is also opaque to charm quarks Heavy quark diffusion, hadron flow & fluctuations →viscosity: h/S = (1 – 3)/ 4p close to conjectured bound • First hint of b decay contributions • bottom quarks maybe not gobbled up by medium?

  33. RHIC II AuAu 20 nb-1 NCC NCC HBD acceptance and ∫L mechanism of eloss g-jet MPC MPC EMCAL VTX & FVTX 0 f 2p EMCAL -3 -2 -1 0 1 2 3 rapidity for further (experimental) progress STAR HFT Si vertex detectors separate c from b and do it again at higher T at the LHC! PHENIX VTX

  34. backup slides

  35. long standing baryon puzzle… STAR coalescence of thermal quarks from an expanding quark gluon plasma. baryons enhanced for 1.5 < pT < 5 GeV/c

  36. Gubser, Pufu, Yarom 0706.4307(hep-th) speculate: ●collectively flowing medium boosts quarks to higher pT ●wake of fast quark builds particle density to coalesce ●baryon enhancement reflects dynamics…?! baryons come from jets – enhanced by wake? Near side meson-meson ●the “extra” baryons have jet-like partners ●only in central collisions do we see a dilution from thermal baryons baryon- meson

  37. sound wave (shoulder) vs. jet remnant away-side total shoulder (medium response) pp collisions jet remnant peripheral central

  38. ratio near/far: nearly constant with centrality! at p+p value! near side increase tracks away side loss of SpT in punch-through balanced by shoulder growth sum associated pT observed in charged particles (line: expected in PHENIX acceptance according to PYTHIA generator) punch-through decreases vs. p+p shoulder grows with centrality near & far totals both increase

  39. Ratio constant with centrality Consistent with p+p value, also with PYTHIA Even though the total vector sum of nearside/awayside both increase, the ratio of the two still hold constant , i. e. the total contribution from “head” and “shoulder” part is hold, but the portion between the two is changing. Ratio of Away pTasso / near pTasso PYTHIA head shoulder Head+shoulder

  40. LPM effect up to O(gs) + (3+1)d hydro + collisions Qin, Ruppert, Gale, Jeon, Moore and Mustafa, 0710.0605 Fix initial state by constraining hydro with particle spectra Reproduce observed energy loss vs. centrality using as = 0.27

  41. d+Au Δ2 0-12% Au+Au 0-12% Au+Au: jet v2=0 Δ2 off-diagonal projection Δ1 Δ1 Df=(Df1-Df2)/2 Three particle correlations • Two Analysis Approaches: • Cumulant Method • Unambiguous evidence for true three particle correlations. • Two-component Jet+Flow-Modulated Background Model • Within a model dependent analysis, evidence for conical emission in central Au+Au collisions pTtrig=3-4 GeV/c pTassoc=1-2 GeV/c From J. Dunlop, Montreal Workshop ‘07 C. Pruneau, QM2006 J. Ulery, HP2006 and poster, QM2006

  42. more complex jet fragment measurements d+Au 0-12% Au+Au Δ2 • 3 – particle correlations • consistent with • Mach-cone shoulder • sum of jet fragment momentum • ▪ increases together • on trigger and away sides • ▪ momentum loss in punch-thru • jet balanced by momentum • in the shoulder peak • ▪ evidence for wakes? Δ1

  43. J/y Karsch, Kharzeev, Satz, hep-ph/0512239 y=0 PHENIX PRL98 (2007) 232301 y~1.7 40% of J/y from c and y’ decays they are screened but direct J/y not? screening length: onium spectroscopy suppression at RHIC very similar to that at SPS! why?? more suppressed at y 0

  44. what does non-perturbative QCD say? Hatsuda, et al. Lattice QCD shows heavy qq correlations at T > Tc, also implying that interactions are not zero Big debate ongoing whether these are resonant states, or “merely” some interactions Color screening – yes! but not fully… Some J/y may emerge intact J/y is a mystery at the moment! Others may form in final state if c and cbar find each other

  45. should narrow rapidity dist. … does it? central peripheral are J/y’s regenerated late in the collision? c + c coalesce at freezeout → J/y R. Rapp et al.PRL 92, 212301 (2004) R. Thews et al, Eur. Phys. J C43, 97 (2005) Yan, Zhuang, Xu, PRL97, 232301 (2006) Bratkovskaya et al., PRC 69, 054903 (2004) A. Andronic et al., NPA789, 334 (2007) J/y is a mystery at the moment!

  46. plasma basics – Debye screening • 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 large • ND= N/VD= rVD VD= 4/3 plD3 1/2 ne = number density e = charge

  47. nee2 wp =------ mee0 1/2 plasma frequency and oscillations • instantaneous disturbance of a plasma → collective motions • plasma wants to restore the original charge neutrality • electrons oscillate collectively around the (heavy) ions • characterized by natural oscillation frequency • plasma frequency • it’s typically high • restoring force: • ion-electron coulomb attraction • damping happens via collisions • if e-ion collision frequency < electron plasma frequency wpe/2p • then oscillations are only slightly damped • a plasma condition: electron collision time large vs. oscillation

  48. Does experiment indicate thermalization? For all distributions described by temperature T and (baryon) chemical potential m: dn ~ e -(E-m)/T d3p Tf ~ 175 MeV

  49. strongly coupled dusty plasma B. Liu and J. Goree, cond-mat/0502009 minimum observed in other strongly coupled systems – kinetic part of h decreases with G while potential part increases minimum h at phase boundary? quark gluon plasma Csernai, Kapusta & McLerran PRL97, 152303 (2006)

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