RHIC Experimental Review

1. RHIC Experimental Review W.A. ZajcColumbia University • Thanks to: • M. Baker, W. Busza, J. Harris, M. Lisa, J. Nagle F.Videbaek, S. White W.A. Zajc

2. To understand fundamental aspects of the strong interaction: Where does the proton get its spin? Why is RHIC? • How does nuclear matter “melt”? • We have a theory of the strong interaction: It works well except when the interaction is strong! W.A. Zajc

3. Connections • QCD is a fundamental theory valid in both the weak and the strong coupling limit • Both aspects are important at RHIC: • Initial state in ion-ion collisions determined by low-x gluons • Thermalization determined by interplay between • (Relatively) few hard gluons carrying most of the energy • “Bath” of numerous but very soft gluons (Baier, Mueller, Schiff and Son) • Final state multiplicities very sensitive to saturation in gluon distributions • Subtle connections between • Chiral symmetry of QCD • Effective field theories of pion-nucleon interaction • Spin structure of the nucleon • Chiral symmetry restoration in heavy ion collisions • “To know the inside of the proton, you must know the outside of the proton” (R. Mawhinney) • “Deconfinement is chirality by other means” (with apologies to Clauswitz) W.A. Zajc

4. Making Something from Nothing • Explore non-perturbative “vacuum” by melting it • Temperature scale • Particle production • Our ‘perturbative’ region is filled with • gluons • quark-antiquark pairs • A Quark-Gluon Plasma (QGP) • Experimental method: Energetic collisions of heavy nuclei • Experimental measurements:Use probes that are • Auto-generated • Sensitive to all time/length scales W.A. Zajc

5. Previous Attempts • First attempt at QGP formation was successful (~1010 years ago) • Since then: Much of physics has been devoted to exploration of “Matter in unusual conditions” The Early Universe, Kolb and Turner From Fermi notes on Thermodynamics W.A. Zajc

6. RHIC’s Experiments STAR W.A. Zajc

7. What’s Different from “Ordinary” Colliders? • Obviously: • Multiplicities • (Cross sections) • But also: • Hermeticity requirements • Rates • Low pT physics • High pT physics • Signals W.A. Zajc

8. Hermeticity • A key factor in “most” collider detectors • Goal of essentially complete event reconstruction • Discovery potential of missing momentum/energy now well established • In heavy ion physics • dNch/dy ~ 1000 • exclusive event reconstruction “unfeasible” • But • Seeking to characterize a state of matter • Large numbers  statistical sampling of phase space a valid approach W.A. Zajc

9. Low pT matters • Heavy ion physics takes place in phase space • Coordinate space as important as momentum space • Measure via identical particle correlations(aka HBT ) • Search for a phase transition in hadronic matter • Characteristic scale LQCD ~ 200 MeV • Flavor dynamics crucial both to transition and to its signatures Low pT Particle Identification (PID) is crucial to QGP Physics W.A. Zajc

10. BRAHMS Acceptance (PID) Acceptances PHOBOS Acceptance STAR Acceptance W.A. Zajc

11. PID Overlaps W.A. Zajc

12. Other Differences • Event characterization • Impact parameter b is well-defined in heavy ion collisions • Event multiplicity predominantly determined by collision geometry • Characterize this by global measures of multiplicity and/or transverse energy • Models • HEP has SM • Reliable predictions of baseline phenomena • HI has only Sub-SM’s… • Even the baseline physics at RHIC and beyond is intrinsically unknown b W.A. Zajc

13. BRAHMS An experiment with an emphasis: • Quality PID spectra over a broad range of rapidity and pT • Special emphasis: • Where do the baryons go? • How is directed energy transferred to the reaction products? • Two magnetic dipole spectrometers in “classic” fixed-target configuration W.A. Zajc

14. BRAHMS Details Forward Spectrometer (rotates 2.5o-30o) • TPC’s: T1 and T2 • DC’s: T3,T4,T5 (not connected) • Magnets: D1,D2,D3,D4 • ToF Hodoscopes: H1, H2 • Cerenkov Counter: C1 • RICH: W.A. Zajc

15. Year 1: Magnet, TPC, CTB, ZDC, RICH Magnet Time Projection Chamber Coils SiliconVertexTracker TPC Endcap & MWPC FTPCs ZDC ZDC VertexPositionDetectors Endcap Calorimeter Central Trigger Barrel or TOF BarrelEMCalorimeter RICH STAR W.A. Zajc

16. STAR Event Data Taken June 25, 2000. Pictures from Level 3 online display. W.A. Zajc

17. Elliptic Flow • Spatial anisotropy in non-central collisions & response of the system to early pressure  emission anisotropy • Elliptic flow predictions from hydro/transport models sensitive to underlying dynamics of initial system • A natural measurement for STAR P.F. Kolb, et al, (QM99) W.A. Zajc

18. centrality STAR Centrality Dependence of Elliptic Flow Differential measure of response to initial geometry PRELIMINARY (scaled) spatial asymmetry W.A. Zajc

19. PHENIX GlobalMVD/BB/ZDC • An experiment with something for everybody • A complex apparatus to measure • Hadrons • Muons • Electrons • Photons Executive summary: • High resolution • High granularity Muon Arms Coverage (N&S) -1.2< |y| <2.3 -p < f < p DM(J/y )=105MeV DM(g) =180MeV 3 station CSC 5 layer MuID (10X0) p(m)>3GeV/c WestArm East Arm South muon Arm North muon Arm Central Arms Coverage (E&W) -0.35< y < 0.35 30o <|f |< 120o DM(J/y )= 20MeV DM(g) =160MeV W.A. Zajc

20. Approaches to QGP Detection 1. Deconfinement R(U) ~ 0.13 fm < R(J/Y) ~ 0.3 fm < R(Y ’ ) ~ 0.6 fm • Electrons, Muons 2. Chiral Symmetry Restoration Mass, width, branching ratio of F to e+e-, K+K- with dM < 5 Mev: • Electrons, Muons, Charged Hadrons Baryon susceptibility, color fluctuations, anti-baryon production: • Charged hadrons DCC’s, Isospin fluctuations: • Photons, Charged Hadrons 3. Thermal Radiation of Hot Gas Prompt g, Prompt g * toe+e-, m+m - : • Photons, Electrons, Muons 4. Strangeness and Charm Production Production of K+, K- mesons: • Hadrons Production of F, J/Y, D mesons: • Electrons, Muons 5. Jet Quenching High pT jet via leading particle spectra: • Hadrons, Photons 6. Space-Time Evolution HBT Correlations of p±p±, K± K± : • Hadrons Summary: Electrons, Muons, Photons, Charged Hadrons W.A. Zajc

21. PHENIX Design W.A. Zajc

22. PHENIX Results ( A sampler ) • Transverse energy spectrum • Charged multiplicity distribution • p0 peak (towards a pT spectrum) pT > 2.5 GeV W.A. Zajc

23. PHOBOS An experiment with a philosophy: • Global phenomena • large spatial sizes • small momenta • Minimize the number of technologies: • All Si-strip tracking • Si multiplicity detection • PMT-based TOF • Unbiased global look at very large number of collisions (~109) W.A. Zajc

24. Hits in SPEC Tracks in SPEC Hits in VTX 130 AGeV PHOBOS Results First results on dNch/dh • for central events • At ECM energies of • 56 Gev • 130 GeV (per nucleon pair) To appear in PRL (hep-ex/0007036) X.N.Wang et al. W.A. Zajc

25. Implications of PHOBOS Results • Constrains (determines!) maximum multiplicities at RHIC energies • Does not constrain centrality dependence of same • Does not (quite) distinguish between • “Saturation” models, dominated by gg g • “Cascade” models, dominated by gg gg, gg ggq ( X.N. Wang and M. Gyulassy, nucl-th/0008014 ) W.A. Zajc

26. ET EZDC ET Determining NPART Best approach (for fixed target!): • Directly measure in a “zero degree calorimeter” • (for A+A collisions) • Strongly (anti)-correlated with produced transverse energy: NA50 W.A. Zajc

27. RHIC ZDC’s • ZDC  Zero Degree Calorimeter • Goals: • Uniform luminosity monitoring at all 4 intersections • Uniform event characterization by all 4 experiments • Process: • Correlated Forward-Backward Dissociation • stot = 11.0 Barns (+/- few %) W.A. Zajc

28. Summary • The initial physics run of RHIC: • Validated the various approaches of each experiment • Has provided all four experiments with quality data sets • Has led to new physics results • Will lead to many more results • DNP: October 4-7, 2000 • Quark Matter (January, 2001) • PRL • Prospects for Year-2 promise even more: • Increased luminosity • New detection channels • And beyond: • P-A • Polarized p-A • Tagged p-p, for example: p+p  n + (p+ + p) D-Y + X W.A. Zajc

29. RIKEN/RHIC/BNL Physics DIS QCD Spin Dynamics Weakmatrixelements LatticeStudies Heavy IonCollisions Astro-physics W.A. Zajc

30. RHIC Luminosity • It’s high! • It’s an equal opportunity parton collider: • Can accelerate essentially all species • Designed for p-p to Au-Au • Asymmetric collisions (esp. p-A) allowed • Good news / bad news: • Permits many handles on systematics • Permits in situmeasurements of “background” p-p and p-A physics • Detectors must handle unparalleled dynamic range in rates and track densities W.A. Zajc

31. Jet Physics at RHIC • Tremendous interest in hard scattering(and subsequent energy loss in QGP) at RHIC • Predictions that dE/dx ~ (amount of matter to be traversed) • Due to non-Abelian nature of medium • But: • “Traditional” jet methodology fails at RHIC • Dominated by the soft background: • For a typical jet cone R = 0.33 (R2 = DF2 + Dh2) have <nSOFT> ~ 64 <ET> ~ 25 GeV • Fluctuations in this soft background swamp any jet signal for pT < ~ 40 GeV: • Solution: • Let R ~0 (PHENIX Dh x Df = 0.01 x 0.01) • Then use high pT leading particles • Investigate by (systematics of) high-pT single particles W.A. Zajc

32. Screening by the QGP In pictures: W.A. Zajc

33. PHOBOS Details • Si tracking elements • 15 planes/arm • Front: “Pixels” (1mm x 1mm) • Rear: “Strips”(0.67mm x 19mm) • 56K channels/arm • Si multiplicity detector • 22K channels • |h| < 5.3 W.A. Zajc

34. Placeholder W.A. Zajc