Quark Gluon Plasma: Experiments with strings attached?

lattice QCD F. Karsch properties of matter l thermodynamic (equilibrium) T, P,  EOS (related T,P,V) v sound, static screening length l dynamic (non-equilibrium)* transport of: particle number, energy, momentum, charge diffusion sound viscosity conductivity * measuring these is a new endeavor! ^ QCD

calculating transport in QGP weak coupling limit strong coupling limit perturbative QCD not so easy! kinetic theory, cascades gravity  supersym 4-d QCD-like theory resummation of hard thermal loops

measuring transport properties: a new challenge l how we measure dynamic properties transport of: particle number, energy, momentum, charge diffusion sound viscosity conductivity l also transverse momentum exchange with the medium: q l emission from the bulk can reflect collective motion l but other useful probes require auto-generation in the heavy ion collision large Q 2 processes to separate production & propagation large E tot (high p T or M) to set scale other than T(plasma) ^

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

The Tools STAR specialty: large acceptance measurement of hadrons PHENIX specialty: rare probes, leptons, and photons

study plasma by radiated & “probe” particles l as a function of transverse momentum p T = p sin  with respect to beam direction) 90° is where the action is (max T,  ) p L midway between the two beams! l p T < 1.5 GeV/c “thermal” particles radiated from bulk of the medium “internal” plasma probes l p T > 3 GeV/c jets (hard scattered q or g) heavy quarks, direct photons describe by perturbative QCD produced early→“external” probe

spectra of pions in p+p and Au+Au p-p PRL 91 (2003) Good agreement with pQCD head-on Au+Au N coll = 975  94

(colored) q & g lose energy, photons don’t

tranport step 1: quantify momentum exchanged l define a transport parameter q: transfer from medium to fast quark/gluon per unit path length l cannot measure directly use data to constrain calculation with varying q do comparison for R AA of high p T pions energy/momentum loss of fast quark to medium dominantly via gluon radiation radiation calculable with pQCD l also calculable via AdS/CFT in that case q is a measure of temperature, T ^ ^ ^ energy/momentum is transferred to the medium how to quantify this & the medium’s response?

extract q using high p T data C. Loizides hep-ph/ v2 a big number! value from AdS/CFT ~4.5 GeV 2 /fm ^

Measuring elliptic flow (v 2 ) dN/d  ~ v 2 (p T ) cos (2  ) + … “elliptic flow” Almond shape overlap region in coordinate space x y z momentum space

v 2 is large & reproduced by hydrodynamics but must use viscosity ~ 0  “perfect” liquid D. Teaney, PRC68, (2003) from AdS/CFT:  /S lower bound is 1/4  can we get at  /S from experiment more directly? data constrains hydro: this is how the plasma physicists do it!

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

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

heavy quarks lose substantial energy pQCD: Wicks, Horowitz, Djordjevic, Gyulassy, NuclPhysA784, 426 (2007) Plasmas have collisions among constituents! including it helps larger than expected scattering  → stronger coupling remains an open question: what about e± from B meson decays??!! e± from heavy quark decay

sufficient interaction to equilibrate?? l This is like putting a rock in a stream and watching if the stream can drag it along… l Measure correlation of e ± with the light hadrons (i.e. v 2 ) l NB: rate of equilibration gives information on the viscosity of the liquid! Heavy quarks do flow!! Use to probe transport properties of QGP! analogy from J. Nagle

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

confronting mechanisms with data PRL98, (2007) Radiative energy loss alone: fails to reproduce v 2 Heavy quark transport model (i.e. diffusion) shows better agreement with R AA and v 2 Even though agreement with data shape is not perfect, slow relaxation ruled out by v 2 Small relaxation time  t  or diffusion coefficient – first direct measurement! D ~ 3/(2  T) for charm Small D → small  /S! more from H. Liu…

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

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

lower p T looks funny: medium responds to the “lost” energy 3<p t,trigger <4 GeV p t,assoc. >2 GeV Au+Au 0-10% preliminary STAR 1 < p T,a < 2.5 < p T,t <4 GeV/c peripheralcentral

lost energy excites a sound (density) wave? if shoulder is sound wave… LOCATION at  +/-1.23=1.91,4.37 → speed of sound c s ~ 0.33 (√0.33 in QGP, 0.2 in hadron gas) relative excitation of sound and diffusion wake in intense study data → sound mode large Gubser, Pufu, Yarom (hep-th) Chesler & Yaffe, (hep-th) strong coupling: ask AdS/CFT answer: yes it does!

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

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

more complex jet fragment measurements l 3 – particle correlations consistent with Mach-cone shoulder l 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 d+Au 0-12% Au+Au Δ2Δ2 Δ1Δ1

conclusions what I know about AdS/CFT … 1/4  l experiments have started to probe plasma transport see significant momentum transfer to/from medium heavy quarks diffuse, losing energy and gaining flow l sound waves? evidence for wakes??? parameterdata saysAdS/CFT predicts transfer q6-24 GeV 2 /fm4.5 GeV 2 /fm viscosity  /s~0 (via  v2)≥ 1/4  (1.6/4  : lQCD) diffusivity D ~3/(2  T)≥ 1/4  speed of sound c s ~ 0.33 (?)QGP: 1/√0.33* hadrons: ~0.2* ^ ?

for further progress STAR HFT PHENIX VTX Si vertex detectors separate c from b rapidity NCC MPC VTX & FVTX  HBD EMCAL RHIC II AuAu 20 nb -1  -jet acceptance and ∫ L mechanism of eloss

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

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

l backup slides

Ratio of Away p T asso / near p T asso l Ratio constant with centrality l Consistent with p+p value, also with PYTHIA l 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. head shoulder Head+shoulder PYTHIA

Au+Au agrees with p+p at resonances (  ) Enhancement for 0.2 < m ee < 0.8 GeV Also excess  →  during hadron gas phase Agree at 1.2 < m < 3 GeV and J/  by coincidence (J/  scales as  0 due to scaling as N coll + suppression) Is the medium hot enough to radiate? p+p and Au+Au normalized to  0 region arXiv: ) measure  * → e+e- pairs

How hot is the medium, anyway? l at RHIC T init ~ 1.5 – 2 T c (~ 300 MeV) indirect! flow, energy loss constrain initial conditions will measure T via radiation of  &  * → e+e- real photons inclusive/hadron decays QCD direct  thermal 

Low mass dilepton excess at RHIC is large submitted to Phys. Rev. Lett arXiv: yield excess grows faster than N  large excess below  q+q →  * → e+e- ? thermal radiation

R.Rapp, Phys.Lett. B 473 (2000) R.Rapp, Phys.Rev.C 63 (2001) R.Rapp, nucl/th/ low mass enhancement at 150 < m ee < 750 MeV 3.4±0.2(stat.) ±1.3(syst.)±0.7(model) Low-mass: Comparison with theory calculations: min bias Au+Au they include: QGP thermal radiation chiral symmetry restoration A. Toia

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 p T trig =3-4 GeV/c p T assoc =1-2 GeV/c off-diagonal projection d+Au 0-12% Au+Au  =(  1  2 )/2 Δ2Δ2 Δ1Δ1 Δ1Δ1 0-12% Au+Au: jet v 2 =0 Δ2Δ2 From J. Dunlop, Montreal Workshop ‘07 C. Pruneau, QM2006 J. Ulery, HP2006 and poster, QM2006

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

what does non-perturbative QCD say? Lattice QCD shows heavy qq correlations at T > T c, 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/  may emerge intact Hatsuda, et al. J/  is a mystery at the moment! Others may form in final state if c and cbar find each other

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

plasma basics – Debye screening l 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 D D =  0 kT n e e 2 Debye sphere = sphere with radius D l number electrons inside Debye sphere is large N D = N/V D =  V D V D = 4/3  D 3 1/2 n e = number density e = charge

plasma frequency and oscillations l 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 l restoring force: ion-electron coulomb attraction l damping happens via collisions if e-ion collision frequency < electron plasma frequency  pe /2  then oscillations are only slightly damped a plasma condition: electron collision time large vs. oscillation n e e 2  p = m e  0 1/2

For all distributions described by temperature T and (baryon) chemical potential   : dn ~ e -(E-  )/T d 3 p Does experiment indicate thermalization? T f ~ 175 MeV

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

Elliptic flow scales with number of quarks transverse KE implication: valence quarks, not hadrons, are relevant pressure field builds early → dressed quarks born of flowing field (as strongly interacting liquids lack well-defined, long-lived quasi-particles)

The acid test for quark scaling  meson (bound state of s+sbar) mass ~ m proton but flows like the mesons PHENIX