1. First PHENIX Results from the Relativistic Heavy Ion Collider Seminar at University of Rochester February 13, 2001 Asst. Prof. James Nagle

2. OutlineOutline Physics goals of the field Physics goals of the field PHENIX experiment at RHIC PHENIX experiment at RHIC Highlight two early physics results Highlight two early physics results Gluon phase space saturation (or not) Gluon phase space saturation (or not) Suppression of high P t hadrons Suppression of high P t hadrons Preview of Year II at RHIC Preview of Year II at RHIC

3. Structure of the Proton Q 2 = 0.1 GeV 2 Q 2 = 1.0 GeV 2 Q 2 = 50.0 GeV 2 x = momentum fraction carried by parton (quark or gluon) What happens when you probe the proton? Deep Inelastic Lepton Scattering

4. Gluon Structure of the Proton When one looks at reasonably high Q 2, the gluons carry about half the proton momentum, but as a large number of low x gluons.

5. Nuclei collide at near the speed of light and a parton cascade results…. Heavy Ion Collider or Gluon Collider

6. QCD Phase Transition QCD potential: in vacuum: linear increase with distance from color charge strong attractive force confinement of quarks to hadrons baryons (qqq) and mesons (qq) in dense and hot matter screening of color charges potential vanishes for large distance scales deconfinement of quarks !

7. Lattice QCD 400 Gflops machine on the 11th floor in Pupin at Columbia The nature of this bath of low relative momentum quarks and gluons cannot be calculated with perturbative QCD. Thus we must rely on lattice QCD calculations. These predict a phase transition to a quark-gluon plasma where the long range confining force is screened.

8. Relativistic Heavy Ion Collisions hadronization initial state pre-equilibrium QGP and hydrodynamic expansion hadronic phase and freeze-out

9. Phase Diagram of Nuclear Matter Color superconducting QCD matter at high density. Relativistic Heavy Ion Collider Large Hadron Collider Early Universe Deconfined Quark-Gluon Plasma Lower energy heavy ion programs at Brookhaven AGS and CERN SPS

10. The universe would have existed in the quark-gluon plasma phase of matter just after the Big Bang. As it expanded and cooled it would have crossed over the phase transition boundary and formed mesons and baryons (hadronization). But it is not easy to reproduce the universe in the laboratory. So instead we collide relativistic speed heavy nuclei. Though some in the press would like to believe otherwise….. “On the Verge of Re-Creating Creation. Then What?” by James Glanz by James Glanz January 28, 2001

11. Relativistic Heavy Ion Collider Au + Au collisions at 200 GeV per nucleon p + p collisions at 500 GeV spin polarized protons lots of combinations in between A little over an hour drive out on the island from Columbia

12. Four Major Experiments STAR

14. PHENIX Experiment Two central arms for measuring hadrons, photons and electrons Two forward arms for measuring muons Event characterization detectors in middle

15. Global Detectors: Event Characterization and Vertex Measure: Beam-Beam Counter Zero Degree Calorimeters Multiplicity and Vertex Detector Central Detectors: Electrons, Photons and Hadrons: Drift Chamber Pixel Pad Chambers Time Expansion Chamber Time-of-Flight Detector Ring Imaging Cherenkov Counter Electromagnetic Calorimeter Forward Detectors: Muons: Cathode Strip Muon Tracker Muon Identifier

16. Data Acquisition

17. First Collisions: June 15, 2000 Technically: 1. STAR 2. PHOBOS 3. PHENIX 4. BRAHMS

18. Exciting Data Taking RHIC machine studies and experiment commissioning: March thru June First collisions: June 15, 2000 at about half beam energy Initial operation (June) with 6+6 bunches yielded 500,000 PHENIX collisions. Final operation at  s NN = 130 GeV (July-September) with 55+55 bunches yielded nearly 45,000,000 PHENIX collisions ! About five million events were put on tape, ~ 3TB of data !

19. (1) Charged Particle Multiplicity Scaling behaviour : binary collisions vs participants 0.2%0.3% qqbar  qqbar 2.0%3.2% qq  qq 26.7%29.8% qg  qg 27.0%24.0% gg  g* 43.0%41.4% gg  gg Au+Aup+p process

20. (1) Collision Characterization “Spectators” “Participants” Many models of particle production identify two components. (A) Soft interactions where production scales with N participants (B) Hard interactions where production scales with N binary Wang, Gyulassy: nucl-th/0008014 Kharzeev, Nandi: nucl-th/0012025 The impact parameter determines the number of nucleons that participate in the collision.

21. Gluon Saturation Eskola, Kajantie, and Tuominen: hep-ph/0009246 However, if you produce too many gluons, the gluons begin to fuse which then limits the produced partons and thus the final hadrons. HIJING is a model with both hard and soft production, but without gluon saturation.

22. Pixel Pad Chambers Project all combinations of hits in Pad Chambers 1 and 3 to Project all combinations of hits in Pad Chambers 1 and 3 to the interaction vertex as determined by the Beam-Beam counters. the interaction vertex as determined by the Beam-Beam counters. Combinatorial background subtraction. Combinatorial background subtraction. B=0

23. Centrality Selection Charged particle track distribution representing 92% (+/- 2% systematic) of the 7.2 barn total Au+Au cross section. We then select event classes based on geometry (number of participating nucleons) using the Zero Degree Calorimeter and Beam-Beam Counter.

24. Some Answers First PHENIX paper submitted! “Centrality Dependence of Charged Particle Multiplicity in Au-Au Collisions at  s NN = 130 GeV” nucl-ex/0012008 Saturation does not appear to set in for peripheral collisions N p ~50 Simple approach implies increasing contribution from hard processes (30% at mid-central and 50% for most central) HIJING model disagrees with overall trend Wang, Gyulassy: nucl-th/0008014 Kharzeev, Nandi: nucl-th/0012025

25. Inter-Experiment Comparison dN/d  /.5N part N part Many more constraints available soon. More phase space More phase space coverage by PHOBOS coverage by PHOBOS Transverse energy Transverse energy scaling by PHENIX scaling by PHENIX Excellent agreement !

26. (2) Jet Physics What is a jet ? Fragmentation of a high-pt quark or gluon Many hadrons produced in a cone hadrons q q leading particle leading particle schematic view of jet production

27. Parton Energy Loss dE/dx  L  E  L 2 Partons are expected to lose energy via gluon radiation in quark-gluon plasma Radiated gluons also hadronize, but the leading particle energy is lower (called jet quenching). Thus, we should look at high P t hadron production.

28. Electromagnetic Calorimeter PHENIX has excellent measurement of high P t  0 using the electromagnetic calorimeter. MIP energy shows excellent agreement with 1995 test beam data Shoulder consistent with antibaryon contribution TOF - (  -flash) < 2.5 nsTOF - (  -flash) > 2.5 ns MIP at 0.271 GeV RMS (MIP peak) = 38 MeV

29.  0 peak   00 p T >2 GeV, asym<0.8

30. PHENIX Spectra Data are preliminary Represent about 1 million minimum bias Au Au events Estimate of number of binary collisions Central = 857 Peripheral = 5.5 Minimum Bias = 220 * 60% systematic error on peripheral estimate

31. What does theory say?

32. Compare to UA1fit(130)

33. Real Questions? Cronin Effect and Pt broadening Cronin Effect and Pt broadening Nuclear shadowing of gluon structure functions Nuclear shadowing of gluon structure functions Nuclear modification of fragmentation functions Nuclear modification of fragmentation functions Other questions ? Other questions ?

34. Nuclear Shadowing 0.2%0.3% qqbar  qqbar 2.0%3.2% qq  qq 26.7%29.8% qg  qg 27.0%24.0% gg  g* 43.0%41.4% gg  gg Au+Aup+p process Nucleon structure functions are known to be modified in nuclei. Gluon shadowing is not measured, but will clearly play a large role.

35. Other Hadrons p T (GeV/c) With a precision Time-of-Flight Wall, PHENIX can identify charged hadrons. Limited initial statistics. Substantial contribution by protons and antiprotons for P t > 2 GeV.

36. Particle Production QED Example: Schwinger mechanism of particle pair production E e + / e - QCD Example: Color electric flux tube (string model) Quantum tunneling from the negative energy continuum

37. FragmentationFragmentation q q q Pair production of qq pairs allows for meson formation. q qq qq Production of qq qq pairs allows for baryon/antibaryon formation. Since the tunneling probability exp[-  (p t 2 +m 2 )/k], there is more meson production. This is observed in jet fragmentation.

38. Preview of Year II at PHENIX Vector mesons J/  ’,  Produced heavy quark anti-quark pairs feel an attractive force and can form these states. However, in the middle of a quark-gluon plasma the attractive force is screened and the heavy vector mesons are expected to be suppressed.

39. System has its own Thermometer Depending on the binding energy of the various states, the state is screened at different temperature scales.

40. J/  and  Trigger OJI Grant for building a Level-2 Trigger to take advantage of upgrades in RHIC luminosity.

41. Exciting physics right now First RHIC run is a success ! Charged Particle Multiplicity results constrain models. Charged Particle Multiplicity results constrain models. Exciting high transverse momentum  0 measurement. Exciting high transverse momentum  0 measurement. And much more…. And much more…. PHENIX is preparing for a second data taking PHENIX is preparing for a second data taking run in April, 2001. RHIC expected to achieve design run in April, 2001. RHIC expected to achieve design luminosity. Also first polarized proton run. luminosity. Also first polarized proton run. Jet quenching measurements beyond P t > 10 GeV ! Jet quenching measurements beyond P t > 10 GeV ! J/  and Y measurement at RHIC ! J/  and Y measurement at RHIC !

43. PHENIX preliminary

44. Calculation of N part and N coll C C Use simulated BBC – ZDC response to define centrality cuts. C C Relate them to N part and N coll using Glauber model. – – Straight-line nucleon trajectories   Constant  NN =(40 ± 5)mb. – – Woods-Saxon nuclear density:

46. PYTHIA calculation for p+p At all transverse momenta the pion yield is greater than the baryon/ antibaryon yield.