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Manuel Ca lderón de la Barca Sánchez Indiana University

How does the strong force, QCD, behave at high energy? How can we study it? What tools do we use? What have we learned?. H o t quarks! : What do we see in Relativistic Heavy Ion collisions “ How to cook the primordial soup”. Manuel Ca lderón de la Barca Sánchez Indiana University.

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Manuel Ca lderón de la Barca Sánchez Indiana University

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  1. How does the strong force, QCD, behave at high energy? • How can we study it? • What tools do we use? • What have we learned? Hotquarks! : What do we see in Relativistic Heavy Ion collisions“How to cook the primordial soup” Manuel Calderón de la Barca Sánchez Indiana University

  2. Disclaimer many of the concepts I will present are “works in very active progress” an unavoidable consequence of exciting, cutting edge science Manuel Calderón de la Barca, P408/508 Seminar

  3. Heavy Ions: How does nuclear matter look at high temperature? High Density QCD Matter in Laboratory Determine its properties QCD Prediction: Phase Transitions Deconfinement to Q-G Plasma Chiral symmetry restoration Relevance to other research areas? Quark-hadron phase transition in early Universe Cores of dense stars High density QCD e ~ 1-3 GeV/fm3 Manuel Calderón de la Barca, P408/508 Seminar

  4. The phase diagram of water • Analogous graphs • superfluids • superconductors • metal/insulator • … Manuel Calderón de la Barca, P408/508 Seminar

  5. Generating a deconfined state • Present understanding of Quantum Chromodynamics (QCD) • heating • compression •  deconfined color matter ! Hadronic Matter (confined) Nuclear Matter (confined) Quark Gluon Plasma deconfined ! Manuel Calderón de la Barca, P408/508 Seminar

  6. Expectations from Lattice QCD /T4 ~ # degrees of freedom confined: few d.o.f. deconfined: many d.o.f. TC ≈ 173 MeV ≈ 21012 K ≈ 130,000T[Sun’s core] Manuel Calderón de la Barca, P408/508 Seminar

  7. How can we study it? Manuel Calderón de la Barca, P408/508 Seminar

  8. Imagine… • You know that ice exists… • Your theory friends with huge computers tell you that there is something called water… • You don’t have a way to heat ice… • So you put millions of ice cubes in an ice-accelerator • Send them at 99.995% of the speed of light to collide • Generating thousands of ice-cube+ice-cube collisions per second… • And you watch it all from the vicinity of Mars! Manuel Calderón de la Barca, P408/508 Seminar

  9. Key Idea: Bulk Matter • We must create/compress/heat a bulk (geometrically large) system • freeze/melt a single H20 molecule? • fundamental distinction from particle physics • Only achievable through collisions of the heaviest nuclei (Au, Pb) at the highest available energy– at RelativisticHeavy Ion Collider (RHIC) 1000’s of particles produced in each collision Manuel Calderón de la Barca, P408/508 Seminar

  10. What tools do we use? How fast? How massive? How long? Detectors and accelerators are our “bread-and-butter”. Manuel Calderón de la Barca, P408/508 Seminar

  11. “RHIC is big” • big facility • big detectors • big collaborations • “big” collisions as seen by the Landsat-4 satellite… Manuel Calderón de la Barca, P408/508 Seminar

  12. PHOBOS BRAHMS RHIC PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC) 1 km v = 0.99995c = 186,000 miles/sec Manuel Calderón de la Barca, P408/508 Seminar

  13. PHENIX ~ 500 collaborators PHOBOS BRAHMS RHIC PHENIX STAR AGS TANDEMS Relativistic Heavy Ion Collider (RHIC) Manuel Calderón de la Barca, P408/508 Seminar

  14. PHOBOS BRAHMS RHIC PHENIX STAR AGS TANDEMS STAR ~500 Collaborators Relativistic Heavy Ion Collider (RHIC) Manuel Calderón de la Barca, P408/508 Seminar

  15. Solenoidal Tracker At RHIC goal: track “all” charged hadrons (bags of quarks) emitted in each collision The STAR Experiment • STAR: Solenoidal Tracker at RHIC • multipurpose detector system for hadronic measurements • large coverage (geometrical acceptance) • tracking of charged particles in high multiplicity environment • measure correlations of observables • study of hard processes (jet physics) Manuel Calderón de la Barca, P408/508 Seminar

  16. Electric field ..generating a cluster of liberated electrons Anode wires with +HV sitting ~5 mm above pads Copper pads ~ 1cm2 “Avalanche” as electrons approach anode wire... V ADC t Amplifying and digitizing electronics connected to each pad bucket # Operation of a Time Projection Chamber Charged particle flies through TPC gas… DAQ SCA/ADC ..capacitively inducing a signal on nearby pads... ..which is amplified, digitized, and recorded for later analysis Manuel Calderón de la Barca, P408/508 Seminar

  17. One collision seen by STAR TPC Momentum determined by track curvature in magnetic field… …and by direction relative to beam Manuel Calderón de la Barca, P408/508 Seminar

  18. Particle momentum from tracking… … how to get particle space-time information?? Manuel Calderón de la Barca, P408/508 Seminar

  19. b = 0  “central collision” many particles produced “peripheral collision” fewer particles produced Impact parameter & Reaction plane Manuel Calderón de la Barca, P408/508 Seminar

  20. b = 0  “central collision” many particles produced “peripheral collision” fewer particles produced Impact parameter & Reaction plane Manuel Calderón de la Barca, P408/508 Seminar

  21. ZDC Paddles/BBC ZDC ZDC Au Au z Paddles/BBC Central Multiplicity Detectors Multiplicity (arb. units) 5% Central x y sNN = 200 GeV STAR Collision Geometry and Centrality Reaction plane peripheral central Non-central Collisions Manuel Calderón de la Barca, P408/508 Seminar Multiplicity

  22. What sorts of things have we learned? • We hoped to create bulk matter, • do we see evidence for collective behaviour? • We hoped to create high density matter, • do we see evidence for dissipative behaviour? Manuel Calderón de la Barca, P408/508 Seminar

  23. How do semi-central collisions evolve? 1) Superposition of independent p+p: momenta pointed at random relative to reaction plane Manuel Calderón de la Barca, P408/508 Seminar

  24. How do semi-central collisions evolve? 1) Superposition of independent p+p: high density / pressure at center momenta pointed at random relative to reaction plane 2) Evolution as a bulksystem Pressure gradients (larger in-plane) push bulk “out”  “flow” “zero” pressure in surrounding vacuum more, faster particles seen in-plane Manuel Calderón de la Barca, P408/508 Seminar

  25. N N   0 0 /4 /4 /2 /2 3/4 3/4 -RP (rad) -RP (rad) How do semi-central collisions evolve? 1) Superposition of independent p+p: momenta pointed at random relative to reaction plane 2) Evolution as a bulksystem Pressure gradients (larger in-plane) push bulk “out”  “flow” more, faster particles seen in-plane Manuel Calderón de la Barca, P408/508 Seminar

  26. Azimuthal distributions at RHIC STAR, PRL90 032301 (2003) b ≈ 6.5 fm b ≈ 4 fm “central” collisions midcentral collisions Manuel Calderón de la Barca, P408/508 Seminar

  27. Azimuthal distributions at RHIC STAR, PRL90 032301 (2003) b ≈ 10 fm b ≈ 6.5 fm b ≈ 4 fm peripheral collisions Manuel Calderón de la Barca, P408/508 Seminar

  28. “v2” Elliptic flow – collectivity& sensitivity to early system • “Elliptic flow” • evidence ofcollective motion • quantified by v2 • geometrical anisotropy momentum anisotropy • sensitive to early pressure • evidence for • early thermalization • QGP in early stage STAR, PRL90 032301 (2003) Hydrodynamic calculation of system evolution Manuel Calderón de la Barca, P408/508 Seminar

  29. A more direct handle? • elliptic flow (v2) and other measurements (in a few slides)  evidence towards QGP at RHIC • indirect connection to geometry • Are there more direct handles on the space-time geometry of collisions? • yes ! Even at the 10-15 m / 10-23 s scale ! • What can they tell us about the QGP and system evolution? • Let’s put Quantum Mechanics to good use! Manuel Calderón de la Barca, P408/508 Seminar

  30. The Bottom line… if a pion is emitted, it is more likely to emit another pionwith very similar momentumif the source is small Creation probability r(x,p) = U*U F.T. of pion source Measurable! probingsource geometry through interferometry p1 r1 x1 p source r(x) 1 m x2 r2 p2 experimentally measuring this enhanced probability: quite challenging 5 fm Manuel Calderón de la Barca, P408/508 Seminar

  31. Au+Au R ~ 6 fm p+p R ~ 1 fm d+Au R ~ 2 fm Correlation functions for different colliding systems STAR preliminary C2(Qinv) Qinv (GeV/c) Different colliding systems studied at RHIC Interferometry probes extremely small scales! Manuel Calderón de la Barca, P408/508 Seminar

  32. p1 Rlong q Rside p2 Rout beam direction More detailed geometry Relative momentum between pions is a vector  can extract 3D shape information Rlong – along beam direction Rout – along “line of sight” Rside –  “line of sight” Manuel Calderón de la Barca, P408/508 Seminar

  33. Timescales • Evolution of source shape • suggests system lifetime is shorter than otherwise-successful theory predicts • Is there a more direct handle on timescales? Manuel Calderón de la Barca, P408/508 Seminar

  34. p1 q p2 Disintegration timescale Relative momentum between pions is a vector  can extract 3D shape information Rlong – along beam direction Rout – along “line of sight”  increases with emission timescale Rside –  “line of sight” Rout Rside Manuel Calderón de la Barca, P408/508 Seminar

  35. Disintegration timescale - expectation 3D 1-fluid Hydrodynamics Rischke & Gyulassy, NPA 608, 479 (1996) with transition with transition “” “” • Long-standing favorite signature of QGP: • increase in , ROUT/RSIDE due to deconfinement  confinement transition • expected to “turn on” as QGP energy threshold is reached Manuel Calderón de la Barca, P408/508 Seminar

  36. 8 8 6 6 RO (fm) 4 4 RS (fm) 1.5 1.25 RO / RS 1.0 increasing collision energy Disintegration timescale - observation • no threshold effect seen • RO/RS ~ 1 RHIC Manuel Calderón de la Barca, P408/508 Seminar

  37. Disintegration timescale - observation • no threshold effect seen • RO/RS ~ 1 • toy model calculations suggest very short timescales Manuel Calderón de la Barca, P408/508 Seminar

  38. What have we learned (part I)? • There is evidence that the system behaves collectively! • Space-momentum correlations consistent with • a very rapidly expanding source • developed in extremely short timescales ~1fm (so short that no models can account for it) Do we know that the system is at high densisty? Manuel Calderón de la Barca, P408/508 Seminar

  39. How can you know it’s high density? • High energy collisions: access to high-momentum transfer processes • High pT particle production • High Mass particle production (Heavy Flavors!) • Name of the game: • Theorists can calculate this for p+p collisions • Check how it is modified in Au+Au collisions Manuel Calderón de la Barca, P408/508 Seminar

  40. jet parton Jets in high energy collisions • fundamental expectation of QCD • occurs in all high energy collisions: e++e-, p+pbar, Au+Au,… • Hard scattering of partons: quarks or gluons drawn from wavefunction of colliding projectiles Free quarks and gluons not observed: high transverse energy partons fragment into collimated sprays (jets) of hadrons nucleon nucleon Manuel Calderón de la Barca, P408/508 Seminar

  41. Manuel Calderón de la Barca, P408/508 Seminar

  42. Partonic energy loss in dense matter Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,… Multiple soft interactions: Gluon bremsstrahlung Opacity expansion: • Strong dependence of energy loss on gluon density glue: • measure DE color charge density at early hot, dense phase Manuel Calderón de la Barca, P408/508 Seminar

  43. in this !!! Find this … jet parton nucleon nucleon p+p jet+jet (STAR@RHIC) Au+Au ??? (STAR@RHIC) Jets at RHIC Manuel Calderón de la Barca, P408/508 Seminar

  44. Partonic energy loss via leading hadrons Energy loss  softening of fragmentation  suppression of leading hadron yield Binary collision scaling p+p reference Manuel Calderón de la Barca, P408/508 Seminar

  45. Leading hadrons at lower energy Central Pb+Pb collisions at CERN SPS (s=20 GeV) p+A collisions: SPS: any parton energy loss effects buried by initial state multiple scattering, transverse radial flow,… Multiple scattering in initial state(“Cronin effect”) Manuel Calderón de la Barca, P408/508 Seminar

  46. nucl-ex/0305015, PRL in press PRL 89, 202301 Au+Au and p+p: inclusive charged hadrons p+p reference spectrum measured at RHIC Manuel Calderón de la Barca, P408/508 Seminar

  47. Suppresion of inclusive hadron yield RAA Au+Au relative to p+p RCP Au+Au central/peripheral nucl-ex/0305015 • central Au+Au collisions: factor ~4-5 suppression • pT>5 GeV/c: suppression ~ independent of pT Manuel Calderón de la Barca, P408/508 Seminar

  48. PHENIX observes a similar effect (p0s) nucl-ex/0304022 lower energy Pb+Pb lower energy a+a Factor ~5 suppression for central Au+Au collisions Manuel Calderón de la Barca, P408/508 Seminar

  49. PHOBOS (h ~ 0.8) and BRAHMS (h ~ 2.0) BRAHMS: nucl-ex/0307003 Also have h = 0 PHOBOS: nucl-ex/0302015 Manuel Calderón de la Barca, P408/508 Seminar

  50. High-pt Evidence • The yield of high pt particles is significantly suppressed in central Au+Au collisions. Manuel Calderón de la Barca, P408/508 Seminar

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