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The Experimental Challenge

STAR. PHENIX. The Experimental Challenge. ONE central Au+Au collision at RHIC. production of MANY secondary particles. p. K. p. J / . p. p. b ~ 0. p. q. projectile. target.  cc. p. p. q. p. p. p. p. p. p. p. e +. p. g. e -.

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The Experimental Challenge

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  1. STAR PHENIX The Experimental Challenge • ONE central Au+Au collision at RHIC • production of MANY secondary particles Axel Drees

  2. p K p J/ p p b ~ 0 p q projectile target cc p p q p p p p p p p e+ p g e- Schematic View of a Heavy Ion Collision • hadrons p, K, p frequent, produced “late” when particles stop to interact • energy density • thermal equilibrium and collective behavior • strangeness equilibration several 1000 particles produced in central collision • electro-magnetic radiation g, e+e-, m+m- rare, emitted “any time”; reach detector unperturbed by strong final state interaction • black body radiation  initial temperature • in-medium properties of mesons  chiral symmetry restoration • “hard” probes J/y, U (->e+e-, m+m-) and jets very rare, created “early” before QGP formation, penetrate hot and dense matter, sensitive to deconfinement • color screening in partonic phase  J/y suppression • energy loss in dense colored matter  jet quenching, absorption Axel Drees

  3. p L e+e- K p jet J/Y g p Freeze-out Hadronization QGP Thermaliztion Hard Scattering Au Au Space-time Evolution of Collisions r time g e  Expansion  space Axel Drees

  4. Spectators Participants Spectators Collisions are not all the same Impact parameter b • Small impact parameter (b~0) • High energy density • Large volume • Large number of produced particles • Measured as: • Fraction of cross section “centrality” • Number of participants • Number of nucleon-nucleon collisions 100% 0 % Axel Drees

  5. Paddles/BBC ZDC ZDC Au Au Paddles/BBC Central Multiplicity Detectors 5% Central Paddle signal (a.u.) STAR Experimental Determination of Geometry Axel Drees

  6. Experimental Program Fixed target experiments with ion beams at two accelerators during past 20 years • AGS at BNL • Si- and Au-beams 2 to 14.6 AGeV • ~ 10 large experiments • hadronic observables all experiments • SPS at CERN • S- and Pb-beams 40 to 200 AGeV • 15 large experiments • charmonium NA30-NA50, NA60 (3rd generation experiment) • electromagnetic probes WA80-98, HELIOS, CERES, NA60 • hadronic observables all other experiments experimental programs basically completed Latest results (in particular NA60) presented at Quark Matter 2008! Axel Drees

  7. Experimental Program New generation of experiments at Ion Colliders • Relativistic Heavy Ion Collider at BNL • Started operation in with 100 GeV beams in 2000 now in 8th year of operation • Au-Au, Cu-Cu, at different energies • p-p (polarized beams) • d-Au • 2 large experiments • PHENIX • STAR • 2 experiments completed • Brahms • PHOBOS • Large Hadron Collider at CERN • begins operation in 2008, first physics in 2009 • One dedicated heavy ion experiment ALICE • HEP experiments ATLAS & CMS with heavy ion programs focus on PHENIX results Axel Drees

  8. E, mu mu E,m E,m Center of Mass Energy • Center of Mass energy measured as nucleon-nucleon equivalent • Fixed target • Examples AGS Au beam of E = 11 GeV s = 4.7 GeV • SPS Pb beam of E = 160 GeV s = 17.4 GeV • Collider • Examples RHIC Au beam of E = 100 GeV s = 200 GeV • LHC Pb beam of E= 2750 GeV s = 5.5 TeV i.e. use nucleon mass mu ~ 939 MeV/c2 Center of mass energy closely related to achievable energy density Highest energy densities created at colliders Axel Drees

  9. BRAHMS PHOBOS RHIC STAR PHENIX Relativistic Heavy Ion Collider Axel Drees

  10. Tandem Accelerator Complex at BNL • Two concentric rings • 6 interaction regions • 3.8 km long • 1740 super conducting magnets RHIC blue and yellow rings booster injector Axel Drees

  11. RHIC Universal QCD Laboratory Accelerate and collide ions from A = 1 to ~ 200 (protons polarized) pp, pA, AA, AB Design PerformanceAu + Aup + p (polarized) Max snn 200 GeV 500 GeV L [cm-2 s -1 ] 8 x 10261.4 x 1031 Interaction rates 1.4 x 103 s -1 3 x 105 s -1 Axel Drees

  12. > 600 members 52 institutions: Axel Drees

  13. Time Projection Chamber Magnet Silicon Vertex Tracker FTPC Vertex Position Detectors STAR Coils TPC Endcap & MWPC FTPC Endcap Calorimeter Barrel EM Calorimeter Central Trigger Barrel / TOF RICH Axel Drees

  14. PHENIX Physics Capabilities designed to measure rare probes:+ high rate capability & granularity + good mass resolution and particle ID - limited acceptance Au-Au & p-p spin • 2 central arms: electrons, photons, hadrons • charmonium J/, ’ -> e+e- • vector mesonr, w,  -> e+e- • high pTpo, p+, p- • direct photons • open charm • hadron physics • 2 muon arms: muons • “onium” J/, ’,  -> m+m- • vector meson -> m+m- • open charm • combined central and muon arms: charm production DD -> em • global detectors forward energy and multiplicity • event characterization Axel Drees

  15. PHENIX Central East Carriage Ring Imaging Cerenkov Drift Chamber Central Magnet West Carriage Axel Drees

  16. ~ 500 members from 64 institutions: 23 USA 11 Japan 6 Korea 5 France 3 China 3 Czech R. 6 Russia 3 Hungary 1 Brazil 2 India 1 Germany 1 Sweden 1 Israel 1 Finland Axel Drees

  17. West Arm tracking: DC,PC1, PC2, PC3 electron ID: RICH, EMCal TOF, Aerogel photons: EMCal East Arm tracking: DC, PC1, TEC, PC3 electron & hadron ID: RICH,TEC/TRD, TOF, EMC photons: EMCal PHENIX Setup as used in 2008 • South & North Arm • tracking: • MuTr • muon ID: • MuID • Other Detectors • Vertex & centrality: • ZDC, BBC, • RxNP, MPC Axel Drees

  18. Estimating the Initial Energy Density Use transverse energy production: • “Highly relativistic nucleus-nucleus collisions: The central rapidity region”, J.D. Bjorken, Phys. Rev. D27, 140 (1983). • Assumes • ~ longitudinal expansion • ~ boost invariance “central rapidity plateau” • Then Element of longitudinally expanding reaction volume: Radius of nucleus R~ 6.5 fm t is formation time ~ 1fm Axel Drees

  19. PHENIX 130 GeV central 2% Initial Energy Density at RHIC Phys. Rev. Lett. 87, 52301 (2001) “Bjorken estimate” relates ET to energy density: Increase by ~1.15 from 130 GeV to 200 GeV initial energy density (formation time t0=1 fm): RHIC Au-Au  i ~ 4.6 GeV/fm3 15 GeV/fm3 SPS Pb-Pb  i ~ 3.0 GeV/fm3 more realistic formation time ~0.3 fm at RHIC ~30 times normal nuclear density~1.5 to 2 times higher than at SPS (s = 17 GeV) Axel Drees

  20. spin isospin degeneracy baryochemical potential temperature at chemical freezeout Final State Hadrochemistry • Thermal yields hadron species • abundances in hadrochemical equilibrium • one particle ratio (e.g. p/p) determines mB/T • a second ratio (e.g. p/p) then determines T • predict all other hadron abundances and ratios final state: hadron gas close to phase boundary Axel Drees

  21. mass m (or velocity) momentum p azimuth f polar angle q beam axis Kinematic Variables for Particle Production measure: • 4-vector of particle • More practical variables: • transverse momentum Lorentz invariant related transverse mass • Rapidity Lorentz transformation: related pseudo rapidity p and q not Lorentz invariant!! Axel Drees

  22. Basic Cross Sections • Inclusive particle production of particle species a (e.g. p,K,p etc.) • Invariant cross section • Typically measured as yield per event differentially in kinematic variable • And studied as function of centrality Axel Drees

  23. Particle Spectra • Chemical equilibrium may imply kinetic equilibrium • first guess: a thermal Boltzmann source: • However, system of interacting particles expands into vacuum • System reasonably well described by hydrodynamic evolution • Collective behavior, radial and “elliptic” flow • Use comparison of hydrodynamic calculation with data to infer input parameters Axel Drees

  24. light 1/mT dN/dmT heavy mT RHIC Spectra - an Explosive Source • different spectral shapes for particles of different mass  strong collective radial flow purely thermal source T explosive source light • reasonable agreement with hydrodynamic prediction at RHIC • Tfo ~ 100 MeV • <br> ~ 0.55 c 1/mT dN/dmT T,b heavy mT mT = (pT2 + m2)½ Full hydro calculation: Initial condition:teq ~ 0.6 fm, Ti ~ 350 MeV, e ~ 20 GeV/fm3 Axel Drees

  25. out-of-plane y Au nucleus in-plane x Au nucleus z Non-central Collisions Elliptic Flow → Early Thermalization • initial state of non-central Au+Au collision • spatial asymmetry • asymmetric pressure gradients • translates into • momentum anisotropy in final state • Fourier expansion • elliptic flow strength • shape “washes out” during expansion, i.e. elliptic flow is “self quenching” • v2 reflects early interactions and pressure gradients Axel Drees

  26. baryons mesons Hadron v2 and more Hydrodynamics • observations at RHIC • v2 is large and for soft hadrons in reasonable agreement with ideal hydrodynamics (not true at lower energies) PHENIX: nucl-ex/0608033 Early thermalization in partonic phase Hadronization (confinement) of constituent quarks! Axel Drees

  27. Key Experimental Probes of Quark Matter • Rutherford experiment a atom discovery of nucleus SLAC electron scattering e  proton discovery of quarks QGP penetrating beam (jets or heavy particles) absorption or scattering pattern Nature provides penetrating beams or “hard probes” and the QGP in A-A collisions • Penetrating beams created by parton scattering before QGP is formed • High transverse momentum particles  jets • Heavy particles  open and hidden charm or bottom • Calibrated probes calculable in pQCD • Probe QGP created in A-A collisions as transient state after ~ 1 fm Axel Drees

  28. 0-12% STAR trigger 2.5-4 GeV, partner 1.0-2.5 GeV hydro vacuum fragmentation reaction of medium peripheral or pp central AuAu Hard Probes: Light quark/gluon jets • Status • Calibrated probe • Strongly modified in opaque medium • Jet quenching • Reaction of medium to probe • (2 particle corr.  Mach cones, etc) • Matter opaque to color charges • Nothing comes out  black hole • extreme density  e ~ 20 GeV/fm3 Many open questions though! Axel Drees

  29. Quark Matter Produced at RHIC III. Jet Quenching I. Transverse Energy Bjorken estimate: t0~ 0.3 fm PHENIX 130 GeV central 2% dNg/dy ~ 1100 initial ~ 10-20 GeV/fm3 II. Flow → Hydrodynamics Initial conditions: therm ~ 0.6 -1.0 fm/c ~15-25 GeV/fm3 Heavy ion collisions provide the laboratory to study high T QCD! Axel Drees

  30. Strongly coupled plasma < 1 fmTi~300 MeV atenergy density 5-25 GeV/fm3 “opaque black hole” thermal radiation jet quenching J/ suppression collective expansion of fireball under pressure memory effect in hadron spectra elliptic flow confinement at phaseboundaryTC ~ 170 MeV in chemical equilibrium relative hadron abundance break down of chiral symmetry modification of meson (r) properties collective expansion ofmemory effect in hadron spectra fireball under pressure transverse flow <v/c> ~ 0.5 thermal freeze-out  > 10 fmTf = 100 MeV end of strong interactiontwo and one particle spectra Quark Matter Formation in Heavy Ion Collisions system evolutionexpectations/observations collisionhard scattering jets, heavy flavor, photons QGP Axel Drees

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