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Introduction to RHIC Science

Introduction to RHIC Science. W.A. Zajc Columbia University. Conclusions. RHIC is a hadron collider of unprecedented versatility. The four RHIC experiments have a broad coverage ideally suited to exploit RHIC’s potential.

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Introduction to RHIC Science

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  1. Introduction toRHIC Science W.A. ZajcColumbia University W.A. Zajc

  2. Conclusions • RHIC is a hadron collider of unprecedented versatility. • The four RHIC experiments have a broad coverage ideally suited to exploit RHIC’s potential. • RHIC and its experiments provide a superb environment for the study of QCD as a fundamental theory: • Phase transition(s) associated with • Confinement • Chiral symmetry breaking • Origin of proton spin W.A. Zajc

  3. Why is RHIC? • To understand fundamental features of the strong interaction: • We have a theory of the strong interaction: • Where does the proton get its spin? • How does nuclear matter “melt”? (This works well except when the interaction is strong…) W.A. Zajc

  4. Phase Diagrams Nuclear Matter Water W.A. Zajc

  5. The Early Universe, Kolb and Turner Previous Attempts First attempt at QGP formation was successful (~1010 years ago) ( Effective number of degrees-of-freedom per relativistic particle ) W.A. Zajc

  6. 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

  7. RHIC Specifications • 3.83 km circumference • Two independent rings • 120 bunches/ring • 106 ns crossing time • Capable of colliding ~any nuclear species on ~any other species • Energy: • 500 GeV for p-p • 200 GeV for Au-Au(per N-N collision) • Luminosity • Au-Au: 2 x 1026 cm-2 s-1 • p-p : 2 x 1032 cm-2 s-1(polarized) 6 3 5 1’ 4 1 2 W.A. Zajc

  8. 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

  9. How is RHIC Different? • It’s a collider • Detector systematics independent of ECM • (No thick targets!) • It’s dedicated • Heavy ions will run 20-30 weeks/year • It’s high energy • Access to perturbative phenomena • Jets • Non-linear dE/dx • Its detectors are comprehensive • ~All final state species measured with a suite of detectors that nonetheless have significant overlap for comparisons W.A. Zajc

  10. 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

  11. 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

  12. Njets pT > 2 GeV/c Uniqueness of RHIC Substantial increase in ECM • Access to high Q2 probes • Dominance of mini-jets • Dominance of gluon collisions To what extent do gluons • Affect particle production (saturation)? • Determine initial entropy production? • Control particle ratios? W.A. Zajc

  13. Gluon saturation at RHIC / xpz 2R dT =  /pT 2R m/pz Longitudinal Transverse When do the gluons overlap significantly? 1 J.P Blaizot, A.H. Mueller, Nucl. Phys. B289, 847 (1987) So for x <  /2Rm Transverse gluon area x A G(x,pT2) • 2 /pT2 > R2with a saturation scale in pT2 ~ A1/3 W.A. Zajc

  14. STAR RHIC’s Experiments W.A. Zajc

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

  16. 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

  17. 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

  18. PHOBOS Result on dNch/dh • 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

  19. 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

  20. BRAHMS Results • First paper to be submitted this week to PRL • Anti-proton to proton yields as a function of rapidity : (Two points are reflected about y=0) • Clear evidence for development of (nearly) baryon-free central region W.A. Zajc

  21. √s [GeV] Approaching the Early Universe • Early Universe: • Anti-proton/proton = 0.999999999 • We’ve created “pure” matterapproaching this value pbar/p • For the first timein heavy ion collisions, more baryons are pair-produced than brought in from initial state NA44 Pb+Pb E866 Au+Au W.A. Zajc

  22. PID Overlaps W.A. Zajc

  23. Agreement between experiments W.A. Zajc

  24. STAR W.A. Zajc

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

  26. (scaled) spatial asymmetry STAR Centrality Dependence of Elliptic Flow Parameterize azimuthal asymmetry of charged particlesas 1 + 2 v2cos (2 f) Evidence that initial spatial asymmetry is efficiently translated to momentum space ( as per a hydrodynamic description) W.A. Zajc

  27. PHENIX W.A. Zajc

  28. PHENIX Results • Excellent consistency between two analyses • Yields grow significantly faster than Nparticipants • Evidence for term ~ Ncollisions • Qualitatively consistent with HIJING • Inconsistent with some saturation models Evidence for highest energy densities yet achieved (~ 5 GeV/fm3) W.A. Zajc

  29. dN/dh / .5Npart Npart Physics, Consistency between Experiments • Trend • incompatible with final-state gluon saturation model • Good agreement with model based on initial-state saturation (Kharzeev and Nardi, nucl-th/0012025) • Excellent agreement between (non-trivial) PHENIX and PHOBOS analyses of this systematic variation with nuclear overlap. W.A. Zajc

  30. pT (GeV/c) pT (GeV/c) Identified Particle Spectra • To what extent do gluons (aka pions) dominate particle production at y=0? • Completely, at least for pT < 2 GeV/c W.A. Zajc

  31. What’s left? The all-important spin program W.A. Zajc

  32. A polarized hadron collider is uniquely suited to some spin measurements: DG via Direct photons Hign pT pions J/Y production via W+/W- production Polarized Drell-Yan RHIC has been equipped To provide polarized beams of protons To make spin measurementsof same in (at least)PHENIX and STAR RHIC Spin Physics W.A. Zajc

  33. This is a world-class program RHIC Spin Potential • Wide range of measurements in many channels to address • DG • Sea quark polarization W.A. Zajc

  34. 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 • Also are subtle connections between • Chiral symmetry of QCD • 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

  35. An Interesting Technical Connection • RHIC experiments are coping with data volumes at the leading edge of current HEP experience: • Run-1 • ~1 Tb per day (recording rate per experiment) • Data volumes ~ 10 Tb (per experiment, from last year) • Run-2 and beyond • Roughly same recording rate (up to x2 higher?) • Greatly increased volumes (multi-100 Tb) • RHIC Computing Facility is a real-world existence proof for data analysis on this scale: • HPSS capacity of ~1.5 petabytes • HPSS optimized file mover • Port of Objectivity to Linux • “Grand Challenge” query processor • ROOT • Key members of development team (Brun, Rademakers, Buncic, Fine) have been supported by NP funds • NP supported contributions to ROOT • Multithreading • Port to SOLARIS • Objectivity encapsulation • StEvent W.A. Zajc

  36. 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

  37. 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

  38. - 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

  39. 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

  40. 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

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

  42. Screening by the QGP In first-order finger physics: • Follow usual derivation of Debye screening • Now put in QGP scales and assumptions: • Hadrons with radii greater than ~ lD will be dissolved • Study “onium” bound states W.A. Zajc

  43. 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

  44. 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

  45. 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

  46. “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

  47. “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

  48. 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

  49. Publication Summary (to date) • BRAHMS • Anti-proton/proton ratio versus rapidity • PHENIX • Charged multiplicity versus participants • Transverse energy production (also versus participants) • PHOBOS • Charged multiplicity in central collisions • Anti-proton/proton ration at y=0 • STAR • Elliptic flow • Anti-proton/proton ration at y=0 • All submissions to PRL • 4 accepted • 3 submitted this week W.A. Zajc

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

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