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Quark Gluon Plasma: the Hottest Matter on Earth

Quark Gluon Plasma: the Hottest Matter on Earth. John Chin-Hao Chen ( 陳勁豪 ) RIKEN Brookhaven Research Center Brookhaven National Laboratory 03/21/2012. Once upon a time…. The universe startsfrom a big bang As time goes by, big fireball starts to cool off

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Quark Gluon Plasma: the Hottest Matter on Earth

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  1. Quark Gluon Plasma:the Hottest Matter on Earth John Chin-Hao Chen (陳勁豪) RIKEN Brookhaven Research Center Brookhaven National Laboratory 03/21/2012 John Chin-Hao Chen

  2. Once upon a time… • The universe startsfrom a big bang • As time goes by, big fireball starts to cool off • 13 billion years later, it is where we are now • What is the very beginning of the universe looks like? • Quark Soup? John Chin-Hao Chen

  3. Outline • What is quark gluon plasma (QGP)? • Some properties of QGP John Chin-Hao Chen

  4. Part I: What is QGP John Chin-Hao Chen

  5. Quarks are confined • Quarks are confined in protons and neutrons • The further quarks apart, the stronger the force; the closer the quarks, the weaker the interaction • What will happen if we increase the energy “high enough”? John Chin-Hao Chen

  6. The Idea of Quark-Gluon Plasma • Typical nucleon energy density (energy inside the nucleon) is about 0.13 GeV/fm3. • Higher temperature → higher energy density → create more new particles (by E = mc2) • When the energy density exceeds 1GeV/fm3, many new particles are made → packed close together • matter will exist not as hadrons (protons, neutrons…), but as independent quarks and gluons. • In this medium, the quarks and gluons are deconfined. • It is called “Quark–Gluon Plasma ” John Chin-Hao Chen

  7. How do we melt the nucleon? But how hotdo we need? John Chin-Hao Chen

  8. How hot do we need? • At critical temperature, TC, the energy density increases rapidly due to the increase of degrees of freedom. (dp-> dQGP) • TC ~ 175MeV. The energy density e~1GeV/fm3. • TC ~ Trillion (1012) K • Temperature of the core of Sun: T~107 K Gas Plasma Energy density / T4 Temperature Phase transition Hadrons John Chin-Hao Chen

  9. Where in the universe can we achieve the extreme condition? • T~1012 K: 1 micro second after the big bang? • Super high pressure: maybe inside the neutron star? • Where else? John Chin-Hao Chen

  10. The Hottest Matter is on Long Island! Collides p+p, Au+Au and other species at various energies!! Maximum energy: Au+Au at s = 200 GeV per nucleon pair John Chin-Hao Chen

  11. What happens in heavy ion collisions • The beams travel at 99.995% the speed of light. • The two ions look flat as a pancake due to Relativity. (g~106 at full energy collision @ RHIC). • The two ions collide and smash through each other for 10-23 s • The collision “melts” protons and neutrons, and liberates the quark and gluons. • Thousands of particles are created and fly out from the collision area; plasma cools off. John Chin-Hao Chen

  12. Two General Purpose Detectors STAR specialty: large acceptance measurement of hadrons PHENIX specialty: rare probes, leptons, and photons John Chin-Hao Chen

  13. Events viewed by detectors John Chin-Hao Chen

  14. PHENIX: Pioneering High Energy Nuclear Interaction eXperiment John Chin-Hao Chen

  15. A even hotter matter at LHC • The Large Heavy Ion Collider • Three experiments: ATLAS, CMS, ALICE (dedicated HI experiment) • Collides Pb+Pb @ √sNN = 2.76/5.5 TeV, and p+p at √s = 2.76 TeV for reference John Chin-Hao Chen

  16. Part II: Some properties of QGP John Chin-Hao Chen

  17. Some properties of QGP will be discussed • Is it hot enough? • Temperature • How does the bulk behave? • Collective flow • How do we probe the QGP • Hard probes John Chin-Hao Chen

  18. How do we understand the properties of QGP? • We collide heavy ions (Au/Pb) which creates QGP • We have most simple system p+p as a baseline measurement • We compare what we see in pp (no QGP) and AuAu (with QGP), see what happened John Chin-Hao Chen

  19. Some useful terminology • Central collision: the two nuclei collide “head on” (0-10% centrality) • Peripheral collision: the two nuclei touch by edge (70-92% centrality) • Npart: Number of nucleons participating the collision • Ncoll: Number of binary collisions • pT : transverse momentum John Chin-Hao Chen

  20. How do we measure the temperature of QGP? • We measured the direct photons from pp and AuAu collisions • We see enhancement of photon yield in AuAu • Similar to black body radiation from QGP!! • T ~ 220 MeV • Tc ~175MeV • Or 4 trillion degrees Celsius • Or 250000 times hotter than the center of the Sun Number of photons enhancement AuAu pp John Chin-Hao Chen

  21. Low pT Direct Photon vs different system rg= (# of direct g) / (# of inclusive g) • Low pT direct photon ratio in various collision systems are measured in PHENIX • large enhancement above pQCD calculations (lines) in AA John Chin-Hao Chen

  22. What is the initial temperature? Tc ~170 MeV • Various theory calculations to describe the data • Tini ~ 300-600 MeV (initial state dependent) • All above Tc (~170 MeV from lattice QCD) John Chin-Hao Chen

  23. How do the particles move? • Collision area has “almond” shape due to overlap geometry of the nuclei. • Almond shape leads to un-uniform momentum distribution. • Pressure gradient pushes the “almond” harder in the short direction. • This is a “hydrodynamic” effect. John Chin-Hao Chen

  24. We can also measure the shape fluctuations • The nuclear is not perfect in shape • Nucleon distribution is not smooth • Azimuthal symmetry of the colliding area no longer available • dN/df 1+S(2vncos n(f-Fn)) • vodd is possible, which is due to shape fluctuations John Chin-Hao Chen

  25. vn(Fn) vs pT • All vn increases with pT • v3 is independent from centrality John Chin-Hao Chen

  26. What is viscosity • Viscosity is the resistivity of the fluid • Low viscosity: milk • High viscosity: honey • Low viscosity means the energy can transfer through the fluid very fast • no viscosity = “ideal fluid” John Chin-Hao Chen

  27. New Tool to Calculate the QGP Properties: String Theory • Through Ads/CFT correspondence, some strongly coupled 4 dimension quantum field theory situation can be transformed in to a black hole in 5 dimensions • By solving the relatively “easy” black hole properties in 5-dim space, we can calculate many properties for strongly coupled system, such as QGP QGP AdS/CFT space John Chin-Hao Chen

  28. v2 and Viscosity • String theory predicts there is a universal minimum on viscosity for strongly coupled system (h/s = 1/4p ~0.08) • QGP: tiny viscosity per particle (h/s ~0.08 in hydrodynamics and under Glauber initial state conditions) • The most perfect fluid in the world!! Phys. Rev. Lett 99, 172301 (2007) John Chin-Hao Chen

  29. vn vs theory • All theory predicts v2 well • v3 adds in additional discrimination power • Data favors Glauber + h/s = 1/4p John Chin-Hao Chen

  30. Other perfect fluid? • Electrons in graphene (2010 Nobel Physics) • T ~ room temperature • Cold atomic gas • T ~ 10-9 K John Chin-Hao Chen

  31. How do the particle flow? • In higher pT, the v2 is saturated • v2 is particle type dependent • The matter is strongly coupled! • v2,M(pT)~2v2,q(pT/2)v2,B(pT)~3v2,q(pT/3) • The quarks have collective motion. John Chin-Hao Chen

  32. Beam energy dependence of vn • Various beam energy: 39, 62, 200 GeV • vn does not have significant beam energy dependence • Hydro dynamical behavior down to 39 GeV John Chin-Hao Chen

  33. Hard probes on QGP • Hard probes • Jets, • Heavy flavor (c, b) • Quarkoniums (J/y, U) • direct photons, • Z/W (LHC) • Usually produced at the beginning to the collision • Probes live through out the whole formation stages John Chin-Hao Chen

  34. What is jet? • When 2 quarks collide, back-to-back jets are produced • Jet is a narrow cone of hadrons and other particles resulting from a fast quark or gluon • In heavy ion collision, the colliding area has high energy and particle density, which will modify the jet passing through this hot and dense medium. • Also called Jet Tomography John Chin-Hao Chen

  35. Jet tomography in daily life– P. E. T. • PET - Position Emission Tomography • Physiologic images based on the detection of radiation from the emission of positron-electron annihilation. PET scan of human brain. Picture from Wikipedia. John Chin-Hao Chen

  36. p-p di-jet Event STAR Jets in the plasma p+p @ 200 GeV Au+Au @ 200 GeV What happened to the jets in the medium ? Where is the jet? John Chin-Hao Chen

  37. How do we study jets? • Best way: • Direct jet measurement (difficult at RHIC) • g-jet (also difficult) • We can also study • High pT single particles (coming from jet fragmentations) • Two particle correlations (leading high pT particles from jet fragmentations, correlated with another lower pT particle) John Chin-Hao Chen

  38. central Ncoll = 975  94 p0 spectra in Au+Au vs. p+p • in central Au+Au collision, less p0 is produced than expected yield from scaled p+p • The yield in Au+Au is suppressed John Chin-Hao Chen

  39. High pT hadrons are suppressed! • RAA : nuclear modification factor • If no “effects”: • RAA = 1 at high-pT where hard scattering dominates • Suppression: • RAA < 1 at high-pT The matter is DENSE. Phys. Rev. Lett. 91, 072301 (2003) John Chin-Hao Chen

  40. Summary of particle suppression @ RHIC • Hadrons (made of quarks) lose energy in the medium • Photons don’t feel strong interactions, so loss no energy in the plasma John Chin-Hao Chen

  41. arXiv:1202.2554 RAA @ LHC • Similar suppression trend till 20 GeV/c • RAA increases with pT when pT > 20 GeV/c • No suppression in photon, Z John Chin-Hao Chen

  42. Awayside jet is suppressed in HI collision! same away Same side, no modification away side, jet is absorbed in the medium Phys. Rev. Lett. 91, 072304 (2003) John Chin-Hao Chen

  43. Jet suppression @ LHC Pb+Pb @ √sNN = 2.76 TeV • Jets are “visible” • Di-jet suppression! • Consistent with RHIC John Chin-Hao Chen

  44. Dijet energy imbalance • AJ=(pT1-pT2)/(pT1+pT2)AJ = 0 means no suppression • Significant suppression in central Pb+Pb collisions John Chin-Hao Chen

  45. g-jet (g-hadron correlation) Low zT High zT zT = pTa/pTt zT ~ -ln(zT) • Use direct photon to tag jet energy to study the energy loss • Jet energy is lost in AA collisions! John Chin-Hao Chen

  46. The shape of the Correlation • Jet shape depends on particle energy • Jet shape is modified by the plasma Phys. Rev. C 78 014901 (2008) John Chin-Hao Chen

  47. Do we see the Mach cone in QGP? • The far side peak moved to ~ 1200 in central collisions! • “Mach Cone” like shape • Sound wave propagate through QGP? • If so, it can be used to estimate the speed of sound in QGP D Phys. Rev. Lett. 98, 232302 (2007) John Chin-Hao Chen

  48. Two particle Dh-Df correlations Peripheral Au+Au Central Au+Au Dh Dh shoulderridge Df Df rad Both near and away side are modified! John Chin-Hao Chen

  49. v3, reason for ridge and shoulder? • Ridge sits at Df ~ 0, shoulder sits at Df~2p/3, 4p/3 • A 3-peak structure! • v3 (Fourier Coefficient of thecos3Df term) gives a natural 3-peak structure • Is v3 the explanation? John Chin-Hao Chen

  50. Jet shape with higher vn modulated background subtraction 200GeV Au+Au 0-20%, inc. g-had. • When v3 modulation is included in the background subtraction, the double peak structure in away-side disappears. John Chin-Hao Chen

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