Introduction to RHIC Physics Upgrades

1. Introduction toRHIC Physics Upgrades W.A. ZajcColumbia University W.A. Zajc

2. Relevant Recommendations • Recommendation 1: The RHIC Program • We recommend full operation of RHIC with the experimental and theoretical tools needed to exploit wholly these novel and unique capabilities in a timely fashion. • Full exploration of the physics program requires operation of RHIC for 37 weeks per year. • Adequate support of experimental and theoretical researchers is essential to realizing the physics promise of this new facility to address fundamental questions of strong interactions. • It is important to pursue targeted opportunities for near-term upgrades to the RHIC detectors,thus extending the kinematic and physics reach of the present program. • Recommendation 2: • A vigorous R&D program to pursue the next generation of accelerator and detector developments needed to elucidate the QCD structure of matter.Two initiatives of primary interest are: a) luminosity upgrade at RHIC to study rare probes of the quark-gluon plasma b) a high-luminosity electron-ion collider to characterize matter at high parton density and measure new spin-dependent features of nucleon structure. • Both initiatives require development of high intensity electron linacs with energy recovery,as well as innovative detection techniques. W.A. Zajc

3. STAR RHIC’s Experiments W.A. Zajc

4. Run-1 Results • RHIC worked (i.e, achieved its Year-1 goals): • Stable operation at 130 GeV • Delivery of 10% of design luminosity • All four experiments worked • All four experiments produced quality data within a few months of initial RHIC operation • Particle yields • Rapidity and pT spectra • Flow • Source sizes (Etc.) • This from a data set equivalent to 1-3 days running of RHIC at design luminosity W.A. Zajc

5. Run-2 Goals • Au-Au running • Achieve design values for • Energy (200 GeV) • Luminosity (2 x 1026 cm-2 s-1) • Interaction region (20 cm) • ~ 10 week physics run • ~ 100 x existing data sets from Run-1 • p-p running • Commission • proton collisions at 200 GeV(5 x 1030 cm-2 s-1) • Polarization for same (  50%) • ~ 5 weeks physics run • (Additional heavy ion running to be determined) W.A. Zajc

6. - Run-2 (A-A) Results • Significantly enhanced detectors  • Much greater integrated luminosity • Greatly extended reach in observables • pT to 20 GeV/c (currently 5 GeV/c) • Spectra of ’s and ’s (currently mass peaks only) • J/Y (no current data) • Extended understanding of RHIC physics • Access truly perturbative regime • Understand detailed hadro-chemistry • Understand (Debye?) screening in hot system W.A. Zajc

7. What’s Left? • Most of the program: • Energy scans • Species scans • All the systematic studies required before laying claim to new physics • Vital spin program • Example (A-A) program to do this: • Run-2: • Au+Au, crude p-p comparison run • First look at J/Y production, high pT • Run-3: • High luminosity Au+Au (60%) of HI time • High luminosity light ions (40%) of HI time • Detailed examination of A*B scaling of J/Y yield • Run-4: • p-d/p-p comparisons • Baseline data for rare processes • Run-5: • “Complete” p-A program with p-Au • Energy scans • Systematic mapping of parameter space W.A. Zajc

8. Physics Upgrades • Significant portions of RHIC physics are luminosity limited • New physics opportunities have appeared since initial design of RHIC experiments • Initial survey of RHIC terrain now provides crucial information for pursuit of background-limited signals • New technologies have emerged since initial design of RHIC experiments W.A. Zajc

9. Running RHIC • It’s dedicated • It’s flexible • Collide ~ any species on ~ any species • Nearly order-of-magnitude range in collision energy • It’s a collider • Detector systematics independent of ECM • Detectors share common fate • Design luminosity modest relative to (thick) fixed-target • Unparalleled control of systematics • With most efficient usage • running at highest possible luminosity • With detectors optimized for • Rare processes • Complementarity W.A. Zajc

10. jet Collision axis g Control (1) Q. How to establish the observed suppression at high pT as a plasma effect? • Answers: • Study it out to highest possible transverse momenta • Study it as a function of flavor and/or color charge of probe • Control initial state geometry • Control initial state parton kinematics  photon-tagged jets • RHIC: one 15 GeV photon / hour (Central Au-Au into Dy = 1) W.A. Zajc

11. RHIC Control (2) • A plasma should exhibit a thermal (Debye) screening length l ~ 1 /gT Q. How to establish that the (to be observed) charmonium suppression pattern results from this mechanism? • Answers: • Study vs. pT • Study vs. centrality • Study in lighter systems • Study vs. a control (a vector meson that should not be suppressed, the Upsilon) W.A. Zajc

12. Vector Meson Rates • 10 weeks of Au-Au running at design luminosity: • 30K J/Y ‘s • Enough for rough • centrality dependence • pT spectra • But very modest with respect to 500K J/Y ‘s in CERN Pb-Pbdata set • x 4 luminosity growth produces ‘CERN-like’ production rate • Major luminosity upgrade required to access this important physics • Upsilon rate ~ 10-3 J/Y W.A. Zajc

13. D0 K-p+ Dalitz and conversions e- D0 K- e+ ne D0 K-m+ nm charm e- beauty e- B0 D-p+ Drell-Yan e- B0 D- e+ ne B0 D-m+ nm D0D0m+m- K+ K-nmnm D0D0 e+e- K+ K-nene D0D0m+e- K+ K-nenm Study by Mickey Chiu, J. Nagle “New” Physics (1) • Increased understanding of open charm significance • Saturation of u,d,s abundances important in establishing thermal properties of system • Chemical equilibrium  no further information on dynamics • Charm (probably) does not chemically equilibrate • Important probe of early dynamics • Important complement to charmonium measurements • Major interest in pursuit of “open charm” as a plasma diagnostic • Currently only very modest capabilities via measurement of high pT leptons • Important to extend with direct detection via displaced vertices W.A. Zajc

14. “New” Physics (2) • Increased appreciation for role of proton-nucleus studies in calibrating plasma signals Example: Strangeness enhancement in p-A, studied versus “centrality” • Increased appreciation for versatility of RHIC as hadron dynamics laboratory Example: Study of Drell-Yan production in p-d vs. p-p (15 weeks each) FNAL E866 PHENIX Central MMS  MMS+MMN W.A. Zajc

15. “Old” Physics • Example: Detection of low mass di-lepton pairs as probes of • Thermal radiation: g *  e+e- • Chiral restoration: r, w  e+e- • Deferred in initial design of RHIC experiments • Unknown backgrounds from mundane sources (Conversion and Dalitz pairs) • Uncertain technical capabilities for “hadron blind” detectors • Now feasible (and remains compelling) W.A. Zajc

16. New Technologies • Si pixel detectors Open charm via displaced vertices • MRPC’s (Multi-gap Resistive Plate Counters) Economical hadron ID over large aperture • (Hydrophobic) Aerogel Flavor tagging at high pT • GEM’s: (Gaseous Electron Multipliers) Economical readout of hadron-blind detectors W.A. Zajc

17. Strengthening the Program Upgrades • Extend physics reach of RHIC • Apply lessons of (recent) past • Access new observables • Increase (already beneficial) overlap and complementarity of the RHIC experiments W.A. Zajc