2. PHENIX OVERVIEW W.A. Zajc Columbia University for the PHENIX Collaboration Special thanks to J. Mitchell (BNL) for animationsanimations

3. 2 Outline l Why Nuclear Physics? l Why RHIC? l Why PHENIX? l Where do we go from here?

4. 3 Central Truths of Nuclear Physics l We are nothing l We are dust l We don’t matter

5. 4 We are nothing (c. 1900) Most of “us” is (nearly) empty space o 99.9% of the mass of atoms is contained in the nucleus o The nucleus is about one-trillionth ( 1/1,000,000,000,000 ) the size of the atom Proton Neutron Quarks Held together by gluons (not shown) Nucleus (“ion” when alone) Atom Key

6. 5 We are dust (c. 1950) l Only the lightest elements (Hydrogen and Helium) were created in the Big Bang l The rest of “us” is stardust o All heavy elements (like the Carbon and Nitrogen we’re made of) were “cooked” together inside stars o Explosions of those (early) stars spread the heavier elements throughout the universe.

7. 6 We don’t matter (c. 2000) l More accurately: We’re not matter l Recall nearly all the mass of each atom is concentrated in the nucleus: o Each nucleus consists of neutrons and protons o Each neutron and proton consists of 3 quarks o Each quark has the mass of about 1% of a proton or neutron(!) o The rest of the mass of protons and neutrons (and hence our mass) is “frozen energy” from the Big Bang

8. 7 Phase Transitions l The “great freeze” took place about 10 millionths of a second after the Big Bang l General name for such phenomena: Phase transition Examples: uSteam to water to ice u(Free quarks and gluons) to (protons and neutrons) to (??)

9. 8 The Big Bang Slowed Down 10,000,000 times

10. 9 Phase Diagrams Water Nuclear Matter

11. 10 A Silly Analogy l Suppose… o You lived in a frozen world where water existed only as ice o and ice comes in only quantized sizes ~ ice cubes o and theoretical friends tell you there should be a liquid phase o and your only way to heat the ice is by colliding two ice cubes o So you form a “bunch” containing a billion ice cubes o which you collide with another such bunch o 10 million times per second o which produces about 1000 IceCube-IceCube collisions per second o which you observe from the vicinity of Mars l Change the length scale by about 10 trillion èYou’re doing physics at RHIC!

12. 11 Boiling Neutrons and Protons l Fundamental Method: Collide heavy nuclei at the highest possible energies: l Fundamental Goals: o Create (new) dense forms of matter o Re-create the quark-gluon phase transition

13. 12 In Pictures

14. 13 l RHIC = Relativistic Heavy Ion Collider l Located at Brookhaven National Laboratory RHIC

15. 14 RHIC’s Experiments STAR

16. 15 How is RHIC Different? l It’s a collider èDetector systematics independent of ECM è(No thick targets!) l It’s dedicated èHeavy ions will run 20-30 weeks/year l It’s high energy èAccess to non-perturbative phenomena uJets uNon-linear dE/dx l Its detectors are comprehensive è~All final state species measured with a suite of detectors that nonetheless have significant overlap for comparisons

17. 16 What is PHENIX? l Pioneering High Energy Nuclear Interaction eXperiment l Goals: o Broadest possible study of A-A, p-A, p-p collisions to uStudy nuclear matter under extreme conditions uUsing a wide variety of probes sensitive to all timescales uStudy systematic variations with species and energy o Measure spin structure of the nucleon èThese two programs have produced a detector with unparalleled capabilities

18. 17 The Collaboration A strongly international venture: è 11 nations Brazil, China, France, Germany, India, Israel, Japan, South Korea, Russia, Sweden, United States è 51 institutions

19. 18 PHENIX at RHIC o 2 central spectrometers o 2 forward spectrometers o 3 global detectors West East South North

20. 19 Schedule o 2 central spectrometers o 2 forward spectrometers o 3 global detectors 1999 2000 2001 2002

21. 20 24-Jul-97

22. 21 10-Jan-98

23. 22 12-Jan-99

24. 23 23-Dec-99

25. 24 Run-1 Configuration l Two central arms o Mechanically ~complete o Roughly half of aperture instrumented l Global detectors o Zero-degree Calorimeters (ZDCs) o Beam-Beam Counters (BBCs) o Multiplicity and Vertex Detector (MVD, engineering run)

26. 25 Tour

27. 26 Tour (Particle View)

28. 27 Run-1 Accomplishments l First collisions:15-Jun-00 l Last collisions: 04-Sep-00 l During this period : o Commissioned uZero-Degree Calorimeters uBeam-Beam Counters uMultiplicity and Vertex Counter uDrift Chambers uPad Chambers uRing Imaging Cerenkov Counter uTime Expansion Chamber uTime-of-Flight Counters uElectromagnetic Calorimeter uMuon Identifier uMinimum Bias Triggers uData Acquisition System o Recorded ~5M minimum bias events

29. 28 Run-1 Results This is a partial compilation

30. 29 Measuring Initial Collision Geometry  Zero Degree Calorimeters (ZDC)  Sensitive to spectator neutrons  common to all four RHIC experiments  Using a combination of the ZDC’s and BBC’s we can define Centrality Classes Zero Degree Calorimeter 5-10% 10-15% 15-20% 0-5 % “Spectators” “Participants”. n n n p p p Beam-Beam Counter (BBC) Impact Parameter ZDC BBC

31. 30 R2R2 Determining Energy Density   Bjorken  ~ 5.0 GeV/fm 3 Roughly 1.5 to 2 times higher than any previous experiments Bjorken formula for thermalized energy density time to thermalize the system (  0 ~ 1 fm/c) ~6.5 fm For the most central events: PHENIX preliminary EMCAL  What is the energy density achieved?  How does it compare to the expect phase transition value ?  Is this energy density thermalized?

32. 31 l Have studied growth of o Number of particles o Energy versus “centrality” l Excellent consistency between two analyses l First evidence for new term in growth ~ number of collisions PHENIX preliminary First Publications

33. 32 Fingerprinting Particles Combined o Tracking o Beam-Beam Counter o Time-of-Flight array provides excellent hadron identification over broad momentum band:

34. 33 Anti-proton/proton ratio

35. 34 Approaching the Early Universe l Early Universe: o Anti-proton/proton = 0.999999999 √s [GeV] PHENIX preliminary E866 Au+Au NA44 Pb+Pb pbar/p l We’ve created “pure” matter approaching this value

36. 35  0 spectra   00 p T >2 GeV,asym<0.8 Systematic errors included Main sources:  peak extraction  PID loss  efficiency calculations  non-vertex pions  pT scale Centrality ~N bin ~N part 10% 800 300 M.B. 125 75 75-92% 10 10 ~ 1M Min Bias AuAU events  s = 130 GeV Peripheral Min bias Central

37. 36 Charged p T Spectra l Systematic trends in high momentum production also studied with charged particles o Much greater statistics o Different systematics

38. 37 Comparison to charged spectra l  0 spectra matches identified charged pion spectra – l A very good internal test of our results (  + +  -) /2 00 All charged

39. 38 Comparison to Theory l Good agreement with “grazing” collisions l For head-on collisions, clear deficit with respect to “no new physics” calculations

40. 39 Central Events – What’s Going On? l “Standard” predictions overestimate the cross-section for  0 by at least  5 dE/dx=0.25 GeV/fm dE/dx = 0 (pQCD) l Predictions including (plasma-like!) energy loss consistent with  0

41. 40 Physics Implications (??) Slide from seminar given last month by M. Gyulassy

42. 41 Physics Impact

43. 42 Composition at high p T Possible complication in comparisons of charged yields to theory: Particle composition is observed to be a strong function of p T

44. 43 Time to Physics Again, learn from the past: First CDF publication: Transverse-Momentum Distributions of Charged Particles Produced in p- pbar Interactions at 630 and 1800 GeV, F. Abe et al., Phys. Rev. Lett. 61, 1819 (1988). l ~One year from data- taking. l Much simpler final state! 6 We will be hard-pressed to reach this goal 5And much harder- pressed to maintain “CDF-like” rate  WRONG!(?)

45. 44 One Year Ago For years we’d been showing pictures of one “central” arm: 21-Jan-00: The real thing moves into place

46. 45 Shape of Things to Come l Completion of Central Arms è Significantly increased aperture l Addition of new capabilities o South Muon Arm o Di-muon physics l Upgraded o Triggers o Data Acquisition èThe ~5M events recorded in Run-1 represent ~1 day of data-taking for RHIC+PHENIX in Run-2 Insert here

47. 46 Shape of Things Now

48. 47 Summary l PHENIX detector has provided outstanding data in first year of RHIC operations o Measured uCharged multiplicity uTransverse energy uElliptic flow uIdentified particle spectra uHBT parameters uHigh p T spectra uInclusive electron spectrum u(much more) o Observed uNew trends in particle production uNew behavior in particle yields at high momentum l Ideally positioned to dramatically extend these results in second year of RHIC running