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

2. Axel Drees “hard” probes J/ ,  (->e + e ,     ) and jets very rare, created “early” before QGP formation, penetrate hot and dense matter, sensitive to deconfinement color screening in partonic phase  J/  suppression energy loss in dense colored matter  jet quenching, absorption electro-magnetic radiation , e + e ,     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 hadrons , K, p frequent, produced “late” when particles stop to interact energy density thermal equilibrium and collective behavior strangeness equilibration Schematic View of a Heavy Ion Collision several 1000 particles produced in central collision b ~ 0 projectile target    p     p   cc JJ       q q ee ee 

3. Axel Drees Space-time Evolution of Collisions e  space time Hard Scattering Au  Expansion  Hadronization  Freeze-out jet J/  QGP Thermaliztion  e+e-e+e- p K   

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

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

6. Axel Drees Experimental Program l AGS at BNL l Si- and Au-beams 2 to 14.6 AGeV l ~ 10 large experiments hadronic observablesall experiments l SPS at CERN l S- and Pb-beams 40 to 200 AGeV l 15 large experiments charmoniumNA30-NA50, NA60 (3 rd generation experiment) electromagnetic probesWA80-98, HELIOS, CERES, NA60 hadronic observablesall other experiments Fixed target experiments with ion beams at two accelerators during past 20 years experimental programs basically completed Latest results (in particular NA60) presented at Quark Matter 2008!

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

8. Axel Drees l Center of Mass energy measured as nucleon-nucleon equivalent l 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 l Collider ExamplesRHIC Au beam of E = 100 GeV  s = 200 GeV LHC Pb beam of E= 2750 GeV  s = 5.5 TeV Center of Mass Energy i.e. use nucleon mass m u ~ 939 MeV/c 2 E, m u mumu E,m Highest energy densities created at colliders Center of mass energy closely related to achievable energy density

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

10. Axel Drees 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

11. Axel Drees RHIC Universal QCD Laboratory Design PerformanceAu + Aup + p (polarized) Max  s nn 200 GeV500 GeV L [cm -2 s -1 ]8 x 10 26 1.4 x 10 31 Interaction rates1.4 x 10 3 s -1 3 x 10 5 s -1 Accelerate and collide ions from A = 1 to ~ 200 (protons polarized) pp, pA, AA, AB

12. Axel Drees > 600 members 52 institutions:

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

14. Axel Drees PHENIX Physics Capabilities l 2 central arms: electrons, photons, hadrons charmonium J/ ,  ’  e  e  vector meson   e  e  high p T       l direct photons l open charm l hadron physics l 2 muon arms: muons “onium” J/ ,  ’,      vector meson      l open charm l combined central and muon arms: charm production DD  e  l global detectors forward energy and multiplicity l event characterization designed to measure rare probes: + high rate capability & granularity + good mass resolution and particle ID - limited acceptance Au-Au & p-p spin

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

16. Axel Drees 23 USA11 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 ~ 500 members from 64 institutions:

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

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

19. Axel Drees Initial Energy Density at RHIC “Bjorken estimate” relates E T to energy density: central 2% PHENIX 130 GeV Phys. Rev. Lett. 87, 52301 (2001) initial energy density (formation time  0 =1 fm): RHICAu-Au  i ~ 4.6 GeV/fm 3  15 GeV/fm 3 SPSPb-Pb  i ~ 3.0 GeV/fm 3 Increase by ~1.15 from 130 GeV to 200 GeV 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)

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

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

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

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

24. Axel Drees mTmT 1/m T dN/dm T light heavy T purely thermal source explosive source T,  mTmT 1/m T dN/dm T light heavy m T = (p T 2 + m 2 ) ½ l different spectral shapes for particles of different mass  strong collective radial flow l reasonable agreement with hydrodynamic prediction at RHIC l T fo ~ 100 MeV ~ 0.55 c Full hydro calculation: Initial condition:  eq ~ 0.6 fm, T i ~ 350 MeV,  ~ 20 GeV/fm 3 RHIC Spectra - an Explosive Source

25. Axel Drees l translates into l momentum anisotropy in final state l Fourier expansion l elliptic flow strength Elliptic Flow → Early Thermalization l initial state of non-central Au+Au collision l spatial asymmetry l asymmetric pressure gradients x z Non-central Collisions in-plane out-of-plane y Au nucleus l shape “washes out” during expansion, i.e. elliptic flow is “self quenching” l v 2 reflects early interactions and pressure gradients

26. Axel Drees Hadron v 2 and more Hydrodynamics l observations at RHIC l v 2 is large and for soft hadrons in reasonable agreement with ideal hydrodynamics (not true at lower energies) mesons baryons Early thermalization in partonic phase Hadronization (confinement) of constituent quarks! PHENIX: nucl-ex/0608033

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

28. Axel Drees Hard Probes: Light quark/gluon jets l Status l Calibrated probe l Strongly modified in opaque medium Jet quenching Reaction of medium to probe (2 particle corr.  Mach cones, etc) hydro vacuum fragmentation reaction of medium 0-12% STAR trigger 2.5-4 GeV, partner 1.0-2.5 GeV peripheral or pp central AuAu Matter opaque to color charges Nothing comes out  black hole  extreme density  e ~ 20 GeV/fm 3 Many open questions though!

29. Axel Drees I. Transverse Energy central 2% PHENIX 130 GeV Bjorken estimate:   ~ 0.3 fm Quark Matter Produced at RHIC  initial ~ 10-20 GeV/fm 3 Initial conditions:  therm ~ 0.6 -1.0 fm/c  ~15-25 GeV/fm 3 II. Flow → Hydrodynamics Heavy ion collisions provide the laboratory to study high T QCD! III. Jet Quenching dN g /dy ~ 1100

30. Axel Drees Strongly coupled plasma  < 1 fm T i ~300 MeV at energy density 5-25 GeV/fm 3 “opaque black hole” thermal radiation jet quenching J/  suppression system evolution expectations/observations collisionhard scattering jets, heavy flavor, photons confinement at phase boundary T C ~ 170 MeV in chemical equilibrium relative hadron abundance break down of chiral symmetry modification of meson  properties collective expansion of memory effect in hadron spectra fireball under pressure transverse flow ~ 0.5 collective expansion of fireball under pressure memory effect in hadron spectra elliptic flow Quark Matter Formation in Heavy Ion Collisions thermal freeze-out  > 10 fm T f = 100 MeV end of strong interaction  two and one particle spectra QGP