Sailing the Perfect Fluid Thomas K Hemmick Stony Brook University
Goals for this Talk • The Friday afternoon seminar should be fun, so PLEASE interrupt as often as you like! • The investigation of new phases of matter formed in Relativistic Nuclear Collisions is very broad…not all aspects can be covered… YUP another overview talk** • I won’t talk formally about another ongoing project (CASE), but you should feel free to ask! **WARNING: The Surgeon General has determined that overview talks contain biased and incomplete reports that may be detrimental to the health and mental wellbeing of individuals who expect or demand otherwise.
Special Relativity Time intervals and physical sizes of objects are not the same to all observers. The speed of any object (distance/time) saturates at the speed of light as energy increases. Quantum Mechanics All entities in the universe are simultaneously particles and waves. Our naïve need to choose one description at a time leads to numerous paradoxes. Two Big Discoveries of 20th Century
General Relativity Mass warps space and time around it creating the appearance of a force. The force generated by warped space-time is gravity. Field Theory Combining Special Relativity with Quantum Mechanics makes Dirac Theory. In this theory both “things” AND forces are made of particle-waves. Two Descendants of These
+ e + e + + e e - e - - e e The “reality” of virtual particles • The diagram above shows the “thought process” of two electrons interacting by playing “Frisbee” with a photon pos • Electrons interact with themselves! • “Dirac” electron has g=2. • Real electron has g-2 ~ 1/400. • The force carriers surround and interact with the bare electron and are “part of” the physical electron. • THE FRISBEES ARE REAL! time
Let’s look at some other particles • The Standard Model lists the particles of nature. • What’s a proton made of: 3 quarks? • What about the particles of the interaction? • A proton is “mostly” the interaction particles!! Simple proton More Realistic
Proton Contents x 100 10-1 10-2 • Parton Distributions • Most quarks & gluons carry a tiny fraction of the proton’s momentum • Like a corporation:There are a few people at the top who make lots of money and many at the bottom who make little. 10-3 Sea Quarks and Gluons 10-4 Parton Distributions • Parton Distributions • No…Part-ahn not Part-uhn • In the strong interaction, the “particles of force” are overwhelming in number. • Each can be considered to carry a fraction “x” of the momentum of a physical proton. • Experimentally the number of sea partons (quarks or gluons) grows as x decreases.
Crisis in Parton Distributions! • The lower in x (lower on corporate ladder) one measures, the more you find. • If the trend continues, the sum of the parts exceeds the whole. • Solution: Color Glass Condensate What happens if you pack too many gluons inside?
probe rest frame r/ ggg Glass at the Bottom of the Sea? • This implies that • Material exhibiting nature’s ultimate gluon density is called Color Glass Condensate. • The existence of this material would cap the gluon growth at low x, saving the theory of the proton. • The Bottom of the Sea Fuses Into Color Glass. • Color Glass is a new phase of matter nature has a maximal gluon density. • Theorists have noted that the gluon fusion reaction, g+gg, “eats gluons”. • Its kind of like a fish tank: • When the fish eat their young, the tank never overfills with fish
Phases of Matter • Solid- • atoms or molecules vibrate in place • constant shape, constant and volume. • Liquid- • molecules flow, but do not disperse • indefinite shape, constant volume • Gas- • molecules diffuse and disperse readily • indefinite shape, indefinite volume • All of three phases exist at approximately room temperature.
Electro-Magnetic Plasma • exists only at temperatures above ~6,000K (if equilibrium is req’d) • exists in the sun and around lightening bolts • electrons separate from nuclei • atoms disassemble and are weakly interacting • however...
Nuclear“Liquid” Temperature Hadron“Gas” Heat Disassembly Incomplete! Boil the Nucleus • electrons, protons, and neutrons are still intact • quarks still bound Question: What’s Next? Answer: Melt the Proton into Quark-Gluon Plasma!
Too hot for quarks to bind!!! Standard Model (N/P) Physics • Collisions of “Large” nuclei convert beam energy to temperatures above 200 MeV or 1,500,000,000,000 K • ~100,000 times higher temperature than the center of our sun. • “Large” as compared to mean-free path of produced particles. 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 SolidLiquidGas Today’s Cold Universe Gravity…Newtonian/General Relativity Stars convert gravitational energy to temperature. They “replay” and finish nucleosynthesis ~15,000,000 K in the center of our sun. Reheating Matter Evolution of the Universe Quark-GluonPlasma??
Phase Diagrams Nuclear Matter Water
STAR Relativistic Heavy Ion Collider (RHIC) • 2 counter-circulating rings, 3.8 km circumference • Any nucleus on any other. • Top energies (each beam): • 100 GeV/nucleon Au-Au. • 250 GeV polarized p-p. • Mixed Species (e.g. d-Au) 4 Complementary Experiments • PHOBOS—Ultra Low PT • BRAHMS—PID at high rapidity • STAR—Large Acceptance Spectrometer • PHENIX—Leptons & Photons
Nuclear Collision Terminology • Centrality and Reaction Plane determined on an Event-by-Event basis. • Npart= # of Participants • 2 394 • Nbinary=# of Collisions Peripheral Collision Semi-Central Collision Central Collision 100% Centrality 0% f Reaction Plane • Fourier decompose azimuthal yield:
The Paradigm • We accelerate nuclei to high energies with the hope and intent of utilizing the beam energy to drive a phase transition to QGP. • The created system lasts for only ~10 fm/c • The collision must not only utilize the energy effectively, but generate the signatures of the new phase for us. • I will make an artificial distinction as follows: • Medium: The bulk of the particles; dominantly soft production and possibly exhibiting some phase. • Probe: Particles whose production is calculable, measurable, and thermally incompatible with (distinct from) the medium.
The Probes Gallery: Jet Suppression charm/bottom dynamics J/Y & U direct photonsCONTROL The importance of the control measurement(s) cannot be overstated!
Thermally-shaped Soft Production “Well Calibrated” Hard Scattering Calibrating the Probe(s) • Measurement from elementary collisions. • “The tail that wags the dog” (M. Gyulassy) p+p->p0 + X hep-ex/0305013 S.S. Adler et al.
AA AA If no “effects”: RAA < 1 in regime of soft physics RAA = 1 at high-pT where hard scattering dominates Suppression: RAA < 1 at high-pT AA RAA Normalization 1. Compare Au+Au to nucleon-nucleon cross sections 2. Compare Au+Au central/peripheral Nuclear Modification Factor: nucleon-nucleon cross section <Nbinary>/sinelp+p
Au-Au s = 200 GeV: high pT suppression! PRL91, 072301(2003) Effect is real…seen by ALL 4 experiments…Final or Initial State Effect?
Proton/deuteron nucleus collision Nucleus- nucleus collision 1st Control Experiment • Collisions of small with large nuclei quantify all cold nuclear effects. • Small + Large distinguishes all initial and final state effects. Medium? No Medium!
Hot vs. Cold: A comparison Au+Au effect: high pT probes disappear in the central events. Is media or initial state effect? d+Au comparison: The same number of collisions per nucleon, but no energy density Not an initial state effect!
q g 2nd Control Experiment • The medium should be transparent to photons. • These thereby probe the initial rate of pQCD production and provide independent normalization of hard collision rates.
So opaque, even a 20 GeV p0 is stopped. • Suppression is very strong (RAA=0.2!) and flat up to 20 GeV/c • Common suppression for p0 and h; it is at partonic level • e > 15 GeV/fm3; dNg/dy > 1100
Escaping Jet “Near Side” Out-plane Lost Jet “Far Side” In-plane Jet Tomography • Jets are produced as back-to-back pairs. • If one jet escapes, is the other shadowed? • Map the dynamics of Near-Side and Away-Side jets. • Vary the reaction plane vs. jet orientation. • Study the composition of the jets • Reconstruct the WHOLE jet • Find “suppressed” momentum & energy. X-ray pictures areshadows of bones Can Jet Absorption be Used to“Take an X-ray” of our Medium?
Back-to-back jets STAR PRL 90, 082302 (2003) Peripheral Au + Au near side Central Au + Au away side peripheral central d + Au control 0 3 Df (radians)
STAR STAR Out-plane In-plane Back-to-Back wrt Reaction Plane • Suppression stronger in the out-of-plane direction. • Indicates suppression depends upon length of medium traversed. • Dilemma: How to quantify “completely opaque”. • Get something to punch through. • Find the lost energy and momentum
Many sides of RAA • Can examine suppression at differing centrality but same medium length (via emission angle) nucl-ex/0611007
Au+Au collisions at 200GeV nucl-ex/0611007 10-20% New scaling parameter Le 50-60% Describes RAA vs angle down to lower pT 50-60% No significant loss for Le < 2 fm Formation time effect? V. Pantuev hep-ph/0506095 V. Pantuev, D. Winter 0-10% Search for the Scaling Variable • SHOCK-1! The data do not scale with rL, differing from the naïve energy loss picture. • SHOCK-2! The data do scale with L alone and show no suppression for L<2 fm Colored Glass???
Enough of this Probe Business… BAM • What does the medium itself have to say?
y py px x y z x Pressure? “elliptic flow” barometer Almond shape overlap region incoordinate space 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
Anisotropic Flow Liquid Li Explodes into Vacuum • Process is SELF-LIMITING • Sensitive to the initial time • Delays in the initiation of anisotropic flow not only change the magnitude of the flow but also the centrality dependence increasing the sensitivity of the results to the initial time. Position Space anisotropy (eccentricity) is transferred to a momentum space anisotropy visible to experiment • Gases explode into vacuum uniformly in all directions. • Liquids flow violently along the short axis and gently along the long axis. • We can observe the RHIC medium and decide if it is more liquid-like or gas-like
Hydrodynamic limit exhausted at RHIC for low pT particles. Can microscopic models work as well? Flow is sensitive to thermalization time since expanding system loses spatial asymmetry over time. Hydro models require thermalization in less than t=1 fm/c Large v2 Adler et al., nucl-ex/0206006
What is needed to reproduce magnitude of v2? Huge cross sections!!
What else we can get from Hydro? So far we have tracked the hydrodynamic evolution of the system back in time to the initial state. Let now Hydro do something good for us. Approximately: ∂nTmn =0 P dV = DEK mT – m0 DKET = √pT2+m02 Baryons Mesons v2 for different m0 shows good agreement with “ideal fluid” hydrodynamics An “ideal fluid” which knows about quarks!
1 < pT (assoc) < 2.5 GeV/c Away Jet cannot “Disappear” • Energy and momentum conservation require that the “lost” jet must be found somewhere. • “Loss” was seen for partner momenta just below the trigger particle…Search low in momentum for the remnants. PHENIX STAR
Correlation of soft ~1-2 GeV/c jet partners Emergence of a Volcano Shape PHENIX (nuclex/0507004) “split” of away side jet! peripheral: normal jet pattern
Explaining Modification of Jet Topology Wake Effect or “sonic boom” Cherenkov Gluon Radiation hep-ph/0411315 Casalderrey-Solana,Shuryak,Teaney nucl-th/0406018 Stoecker hep-ph/0503158 Muller,Ruppert nucl-th/0503028A. K. Chaudhuri Renk & Ruppert Phys. Rev. C73 011901 (2006) nucl-th/0507063 Koch, Majumder, X.-N. Wang Transport Theory nucl-th/0601012 Ma, Zhang, Ma, Huang, Cai, Chen, He, Long, Shen, Shi Mult. Scat. nucl-th/0605054 Chiu & Hwa Jets and Flow couple hep-ph/0411341 Armesto,Salgado,Wiedemann
Mach cones common in EM plasma Experimental Handle:3-particle correlations
near near near Medium Medium Medium away away π away di-jets 0 π 0 deflected jets mach cone Conical Flow vs Deflected Jets
signal obtained by subtraction of dominant backgrounds flow components, jet-related two-particle correlation clear elongation (jet deflection) off-diagonal signal related to mach cone? Jason Ulery -- Purdue Renk&Ruppert: Some of both OK Three-Particle Correlations Au+Au Central 0-12% Triggered Δ2 _ _ = Raw – Jet x Bkgd – Bkgd x Bkgd (Hard-Soft) (Soft-Soft incl. Flow) Δ1 Some of both patterns
What about near side? New phenomenon called “Ridge” is seen at RHIC clearly associated with jets, i.e. hard processes. The Ridge yield (per trigger) scales with Npart same as soft particle production does. Ridge phenomenon is consistent with the energy loss by a near surface jets in an opaque media. 43
What is a “Perfect” Fluid? • Perfect Fluid: • all points move in lock-step. • School of minnows that change direction together. • The whole fluid pushes back. • Imperfect Fluid: • Turbulence. • Only nearby fluid slows the boat. • Fluid Perfection Measurement • Slowing a light quark requires a little fluid. • Slowing a heavy quark requires a lot of fluid. • Result: Charm Quark Flows!
How Perfect is “Perfect” ? • RHIC “fluid” is at ~2-3 on this scale (!) • The Quark-Gluon Plasma is the most perfect fluid ever observed. • But WHY??? T=1012 K
How to make the most perfect fluid • Start with the strongest interaction you can get. • Pack the particles as tight as they can go: !?!? COLOR GLASS CONDENSATE !?!?!
To Summarize T ~ 200- 400 MeV The hottest densest matter ever studied in the laboratory flows as a (nearly) perfect fluid with systematic patterns consistent with quark degrees of freedom and a viscosity to entropy density ratio lower (?) than any other known fluid with a value near (?) a conjectured quantum bound ei ~ 30-60 eo (thermal yields) large “elliptic” flow valence quark scaling h/s ~ (2-3) /4p
Thomas K Hemmick Stony Brook University Sailing the Perfect Fluid
2nd to Last Comment: • Coals to New Castle • Doug Fields • Bernd Bassalleck