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Columbia University

Flying High with Surveying the Landscape for Quark-Gluon Plasma and the Secrets of the Proton’s Spin. Columbia University. Christine Aidala. Vassar College. December 8, 2003. Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) at the Relativistic Heavy Ion Collider (RHIC).

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Columbia University

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  1. Flying High with Surveying the Landscape for Quark-Gluon Plasma and the Secrets of the Proton’s Spin Columbia University Christine Aidala Vassar College December 8, 2003

  2. Pioneering High Energy Nuclear Interaction eXperiment (PHENIX) at the Relativistic Heavy Ion Collider (RHIC) C. Aidala, Vassar College, 12/8/03

  3. RHIC at Brookhaven National Laboratory C. Aidala, Vassar College, 12/8/03

  4. STAR RHIC’s Experiments C. Aidala, Vassar College, 12/8/03

  5. What Are We Investigating at RHIC? Connecting Quarks with the Cosmos Eleven Science Questions for the New Century • Report from the Committee on the Physics of the Universe for the National Research Council of the National Academies • 8th question: What are the new states of matter at exceedingly high density and temperature? C. Aidala, Vassar College, 12/8/03

  6. The Beginning of Time • Time began with the Big Bang: • All energy and matter of the universe was in a state of intense heat and compression. • Since then the Universe has cooled • While cooling, the material of the universe underwent several phase changes. • 2.7 Kelvin is the temperature of most of the universe today. • However, there exist a few “hot spots” where the expanding matter has collapsed back in upon itself. • What can we learn from laboratory experiments about this early evolution of the Universe? C. Aidala, Vassar College, 12/8/03

  7. ~ 10 ms after Big Bang Hadron Synthesis strong force binds quarks and gluons in massive objects: protons, neutrons mass ~ 1 GeV Theory of Strong Force: QCD: Quantum Chromo Dynamics two fundamental puzzles occur at the hadron synthesis confinement of quarks  quarks form hadrons broken chiral symmetry  hadrons become massive ~ 100 s after Big Bang Nucleon Synthesis protons and neutrons bind in nuclei C. Aidala, Vassar College, 12/8/03

  8. • Quarks are held together by exchanging colored gluons V~1/r at short distance V~kr at long distances • We say that quarks and gluons are confinedin hadrons – mesons & baryons Hadrons are made of confined quarks and gluons with net zero color Hadrons interact by exchanging other hadrons pion proton proton The Strong Force and Quantum Chromodynamics (QCD) C. Aidala, Vassar College, 12/8/03

  9. Exploring QCD at RHIC • The strong coupling in QCD presents challenges for performing theoretical calculations and making fundamental experimental measurements • The heavy ion program at RHIC seeks to create strongly interacting matter at unprecedented temperatures and densities • The quark-gluon plasma (QGP) (if it exists!) is a deconfined state of QCD matter, in which quarks and gluons are asymptotically free • A new regime in which to study strongly interacting matter! • The polarized proton program at RHIC seeks to understand the spin of the proton in terms of the angular momenta of the (confined) quarks and gluons which constitute it C. Aidala, Vassar College, 12/8/03

  10. The Relativistic Heavy Ion Collider • Primarily designed to collide heavy ions • Main design purpose: search and discovery mission for quark-gluon plasma • Most versatile collider in the world! Nearly any species can be collided with any other. • asymmetric species possible due to independent rings with separate steering magnets • First polarized proton collider in world! Special magnets and other equipment installed to measure and maintain polarization. C. Aidala, Vassar College, 12/8/03

  11. RHIC Specifications • 3.83 km circumference • Two independent rings • 120 bunches/ring • 106 ns crossing time • 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) C. Aidala, Vassar College, 12/8/03

  12. How is RHIC Different? • Different from p-p, e-p colliders • Atomic weight A introduces new scale Q2 ~ A1/3 Q02 • Different from previous (fixed target) heavy ion facilities • ECM increased by order-of-magnitude • Accessible x (parton momentum fraction) decreases by ~ same factor • Access to perturbative phenomena • Its detectors are comprehensive • Four RHIC detectors designed to have some unique capabilities yet significant overlap for comparisons s = Center-of-mass energy (per nucleon collision) pT = transverse momentum = |p| sin q Q2 = (momentum transfer)2 C. Aidala, Vassar College, 12/8/03

  13. Heavy Ion Collisions at RHIC • We’re interested in whether the most head-on Au-Au collisions are simply like 197 superimposed p-p collisions, or whether there are new effects • Proton-proton collisions serve as a “baseline” comparison • Also compare proton-Au (actually deuteron-Au) collisions to look for possible effects of “cold” nuclear matter • Same energy at same accelerator and detector help cancel systematic uncertainties in comparisons C. Aidala, Vassar College, 12/8/03

  14. Predicting pT Distributions at RHIC • Focus on some slice of the collision: • Assume 3 nucleons struck in A, and 5 in B • Do we weight this contribution as • Npart ( = 3 + 5) ? • Ncoll ( = 3 x 5 ) ? • Answer is a function of pT : • Low pT  large cross sections  yield ~Npart • Soft, non-perturbative, ... • High pT small cross sectionsyield ~Ncoll • Hard, perturbative, “binary scaling”, ... C. Aidala, Vassar College, 12/8/03

  15. Binary collisions Participants Spectators Spectators Participants Spectators Impact Parameter (fm) Systematizing our Knowledge • Determine • the number of participating nucleons NPARTin each collision(and thus the impact parameter) • The number of binary nucleon-nucleon collisions NCOLL as a function of impact parameter • Often express impact parameter b in terms of “centrality” e.g. 10-20% most central C. Aidala, Vassar College, 12/8/03

  16. PHENIX • Pioneering High Energy Nuclear Interaction eXperiment • Goals: • Broadest possible study of A-A, p-A, p-p collisions to • Investigate nuclear matter under extreme conditions • Using a wide variety of probes sensitive to all timescales • Examine systematic variations with species and energy • Explore the spin of the proton • A collaboration, a detector, an experiment C. Aidala, Vassar College, 12/8/03

  17. PHENIX the Collaboration 12 Countries; 57 Institutions; 460 Participants C. Aidala, Vassar College, 12/8/03

  18. PHENIX the Detector • Philosophy: • High rate capability & granularity • Good mass resolution and particle ID • Sacrifice acceptance • 2 central spectrometers • - Track charged particles and detect electromagnetic processes • 2 forward spectrometers • - Identify and track muons • 3 global detectors • - Determine when there’s a collision C. Aidala, Vassar College, 12/8/03

  19. Run Year Species s1/2 [GeV ] Ldt Ntot P 01 2000 Au-Au 130 1.0 mb-1 10M 02 2001/2002 Au-Au 200 24 mb-1 170M p-p 200 0.15 pb-1 3.7G ~15% 03 2002/2003 d-Au 200 2.74 nb-1 5.5G p-p 200 0.35 pb-1 6.6G ~27% PHENIX Run History 2000 2002/2003 2001/2002 C. Aidala, Vassar College, 12/8/03

  20. Au-Au and d-Au collisions in the central arms 2001/2002 Au-Au 2002/2003 d-Au C. Aidala, Vassar College, 12/8/03

  21. How do we compare heavy ion collisions to proton-proton collisions? • Recall: Npart ( = 3 + 5) • Ncoll ( = 3 x 5 ) We measure particle yields: Then we define ratios: “Central” collisions: head on “Peripheral” collisions: grazing These ratios indicate the effect of the nuclear medium on the yields C. Aidala, Vassar College, 12/8/03

  22. Systematizing Our Expectations = 1 for “baseline expectations”> 1 “Cronin” enhancements (seen previously in proton-nucleus collisions)< 1 (at high pT) “anomalous” suppression no effect  C. Aidala, Vassar College, 12/8/03

  23. New Effect Seen at RHIC! • Results from first RHIC run showed that production of hadrons at high transverse momentum in central collisions is suppressed Brookhaven Science AssociatesU.S. Department of Energy C. Aidala, Vassar College, 12/8/03

  24. An Example of Ncoll Scaling • PHENIX (Run-2) data on p0 production in peripheral collisions: • Excellent agreement between PHENIX measured p0’s in p-p and PHENIX measured p0’s in Au-Au peripheral collisions scaled by the number of collisionsover ~ 5 decades PHENIX Preliminary C. Aidala, Vassar College, 12/8/03

  25. Where Ncoll Scaling Doesn’t Work: Central Collisions • Central collisions are different.(Huge deficit at high pT) • This is a clear discoveryof new behavior at RHIC • It is presumably a result due to formation of unusually dense and opaque matter early in the collision PHENIX Preliminary C. Aidala, Vassar College, 12/8/03

  26. Proton/deuteron nucleus collision Nucleus- nucleus collision d+Au Control Experiment • Collisions of small with large nuclei were always foreseen as necessary to quantify cold nuclear matter effects. C. Aidala, Vassar College, 12/8/03

  27. RAA vs. RdAu for Identified p0 Initial State Effects Only d+Au Initial + Final State Effects Au+Au d-Au results rule out initial state effects as the cause of the suppression C. Aidala, Vassar College, 12/8/03

  28. d+Au results from presented at a press conference at BNL on June 18th, 2003 Some Excitement this June C. Aidala, Vassar College, 12/8/03

  29. Conclusions Thus Far • The combined data from Runs 1-3 at RHIC on p-p, Au-Au and d-Au collisions establish that a new effect (a new state of matter?) is produced in central Au-Au collisions Au + Au Experiment d + Au Control Experiment Final Data Preliminary Data C. Aidala, Vassar College, 12/8/03

  30. Polarized Proton Collisions and Spin Physics at RHIC • World’s first polarized proton collider! • RHIC has been equipped with devices to maintain the protons’ polarization through acceleration and storage in the rings • Also equipped to measure the degree of polarization C. Aidala, Vassar College, 12/8/03

  31. Proton Structure and the Quark-Parton Model • Simplest model: a proton is made of three valence quarks—2 up quarks and 1 down • Confinement: these quarks are not free in the nucleon! • As you hit the proton harder, you resolve shorter-lived fluctuations: gluons and sea quarks. Quarks are fermions with spin 1/2. C. Aidala, Vassar College, 12/8/03

  32. Proton Quark Spin Gluon Spin Spin Orbital Angular Momentum The Proton Spin Crisis Suppose have a proton with total spin +1/2 along some axis. Would naively expect it to contain two quarks with spin +1/2 and one with spin -1/2. 1/2 + 1/2 - 1/2 = +1/2 Surprising data from polarized muon-nucleon scattering in late 1980s! 1987: Only 12% +- 16% of proton’s spin carried by quarks! The proton spin crisis begins!! The rest now expected to be from gluon spin and orbital angular momentum of quarks and gluons, but this hasn’t been easy to measure! C. Aidala, Vassar College, 12/8/03

  33. Experimental data on proton structure polarized unpolarized g1 F2 Data points on polarized structure function much sparser! C. Aidala, Vassar College, 12/8/03

  34. Polarized quark and gluon distributions M. Hirai et al (AAC collab) up quarks sea quarks down quarks gluon C. Aidala, Vassar College, 12/8/03

  35. Goals of the Spin Program • Determine the complete spin structure of the nucleon • In particular, contributions from • Gluon polarization (DG) • Sea-quark polarization (Du , Dd) • Why RHIC? • High energy  factorization • Polarized hadrons  gq, gg collisions • High energy  new probes (W’s) C. Aidala, Vassar College, 12/8/03

  36. Production Heavy Flavors Prompt Photon Proton Spin Structure at PHENIX C. Aidala, Vassar College, 12/8/03

  37. RHIC pC Polarimeters BRAHMS & PP2PP PHOBOS PHENIX STAR Spin Rotators Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 500 mA, 300 ms AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles RHIC as a Polarized Proton Collider “Blue” and “yellow” rings Run-2 configuration installed for Run-3 Siberian Snakes C. Aidala, Vassar College, 12/8/03

  38. First Two Spin Runs at RHIC • 2001-2 • Transversely polarized p+p collisions • Average polarization of ~15% • 2003 • Longitudinally polarized p+p collisions achieved • Average polarization of ~26% Different spin combinations for different crossings aid in canceling systematic uncertainties. C. Aidala, Vassar College, 12/8/03

  39. Spin Rotators OFF Spin Rotators ON, Current Reversed Yellow Blue Blue Yellow Spin Rotators ON, Correct! Spin Rotators ON, Almost… PB=35.5% PY=37% |P|=30%, PT=0%  PL=30% |P|=37%, PT=24% PL=28% Blue Yellow Yellow Blue Local Polarimeter at PHENIX Run-03 Local polarimeter allowed us to determine the direction of the protons’ spin at our experimental area. Spin rotators were effective in taking the polarization vector from transverse to longitudinal! C. Aidala, Vassar College, 12/8/03

  40. p0 Cross Section from 2001-2 Run accepted by PRL, hep-ex/0304038 • Statistics cover eight orders of magnitude • Next-to-leading-order perturbative QCD applies above transverse momentum of 2 GeV/c at RHIC • Will be able to use in interpretation of spin-dependent results 9.6% normalization error not shown C. Aidala, Vassar College, 12/8/03

  41. Versus Spin Measurements: Looking at Asymmetries Collide polarized protons in different configurations and see what we observe in our detector. Double longitudinal spin asymmetries: Single transverse spin asymmetries: C. Aidala, Vassar College, 12/8/03

  42. Production Leading hadrons as jet tags Hard Scattering Process qg+gq qq gg C. Aidala, Vassar College, 12/8/03

  43. Some First Spin Results B.Jaeger et al., PRD67, 054005 (2003) • Double longitudinal asymmetry for neutral pions has been measured • Preliminary results released September 2003 • Gives a handle on gluon polarization • Food for thought for theorists! C. Aidala, Vassar College, 12/8/03

  44. What’s Next Heavy ion program • Investigate other probes that look deeply into the medium to characterize it. • The rare processes probe the medium: • Heavy Quark States • Dissolution of J/Y & Y’: the bound states of charm-anticharm quarks probe quark deconfinement. • Electromagnetic Probes (no strong interaction) • Direct photons, e+e-, m+m-: lack of strong interaction allows them to penetrate the dense QCD medium • Long Au+Au run starting later this month! Spin program • Cleaner measurement of gluon polarization via direct photon double longitudinal asymmetry • Probe polarization of sea quarks via W boson measurements • Long spin run planned for 2005 C. Aidala, Vassar College, 12/8/03

  45. Summary • Successful first three years at RHIC and PHENIX! • Have shown that medium produced in 200 GeV heavy ion collisions is fundamentally different through comparison to both p-p and d-Au collisions • Further exploration of this medium and potential identification as QGP from upcoming Run-04 data and beyond • Many open questions remain! • Will need high luminosity to access a variety of rare processes and answer these questions • RHIC has been successful as the world’s first polarized proton collider, opening up new kinematic regions for investigating the spin of the proton • The first spin results from PHENIX are out and stimulating discussion within the theoretical community Many more years of exciting data and results to look forward to! C. Aidala, Vassar College, 12/8/03

  46. Extra Slides C. Aidala, Vassar College, 12/8/03

  47. Making Something from Nothing • Explore non-perturbative “vacuum” that confines color flux by melting it • Experimental method: Energetic collisions of heavy nuclei • Experimental measurements:Use probes that are • Auto-generated • Sensitive to all time/length scales • Particle production • Our ‘perturbative’ region is filled with • gluons • quark-antiquark pairs which screen the “bare” interaction • A Quark-Gluon Plasma (QGP) C. Aidala, Vassar College, 12/8/03

  48. Kinematics Dynamics Basic Kinematics Fundamental single-particle observable: Momentum Spectrum C. Aidala, Vassar College, 12/8/03

  49. Collision Geometry -- “Centrality” Spectators Participants For a given b, Glauber model predicts Npart (No. participants) and Nbinary(No. binary collisions) C. Aidala, Vassar College, 12/8/03

  50. The PHENIX Detector • Philosophy: • High rate capability & granularity • Good mass resolution and particle ID • Sacrifice acceptance Central Arm Tracking Drift Chamber, Pad Chambers, Time Expansion Chamber Muon Arm Tracking Muon Tracker Calorimetry PbGl and PbSc Particle Id Muon Identifier, RICH, TOF, TEC Luminosity Counters/Vertex Detectors BBC, ZDC/SMD, Local Polarimeter, forward hadron calorimeters, NTC, MVD DAQ High bandwidth Trigger Level 2 Level 1 (GL1P, muId, EMC/RICH) Online Calibration and production C. Aidala, Vassar College, 12/8/03

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