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Results from the PHOBOS Experiment at RHIC - A Perspective Russell Betts – UIC for

Results from the PHOBOS Experiment at RHIC - A Perspective Russell Betts – UIC for The PHOBOS Collaboration. The PHOBOS Perspective on Discoveries at RHIC The PHOBOS White Paper nucl-ex/0410022. Outline of the Talk. The PHOBOS Experiment The Data and Analysis

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Results from the PHOBOS Experiment at RHIC - A Perspective Russell Betts – UIC for

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  1. Results from the PHOBOS Experiment at RHIC - A Perspective Russell Betts – UIC for The PHOBOS Collaboration

  2. The PHOBOS Perspective on Discoveries at RHIC The PHOBOS White Paper nucl-ex/0410022 Outline of the Talk • The PHOBOS Experiment • The Data and Analysis • The Nature of the Matter formed in AA Collisions • Discovery of Simple Scaling Rules

  3. The PHOBOS Experiment (2004) • 44-p Multiplicity Detector • MMagnetic Spectrometer + TOF T0 counter SpecTrig TOF Paddle Trigger Counter Octagon Spectrometer NIM A 499 (2003) 603

  4. Multiplicity and Trigger Detectors Octagon Paddle Trigger Counter ZDC Ring Counter

  5. Counting Particles Bulk of Particles pT<1GeV

  6. Vertex Tracklets (I) Tracklets are two point tracks that are constrained by the event vertex. dh = h1 – h2 df = f1 – f2 Vertex Detector Event Display |dh| < 0.04 |df| < 0.3

  7. Vertex Tracklets (II) All Pairs of Hits

  8. f -3 0 +3 -5.5 h +5.5 Hit Counting (I) Octagon, Ring and Vertex Detectors (unrolled) Count Hits or Deposited Energy

  9. 12 12 DE (“MIP”) 8 8 4 4 0 0 6 6 0 0 -6 2 4 -6 -4 2 4 -4 -2 -2 Discriminating Background DE vs. h in the Octagon Monte Carlo Data DE (“MIP”) h h Not from Vertex Si From Vertex

  10. 0-3% Octagon (central) Rings Ntracks/hit pad 50-55% (peripheral) h Measure the Occupancy Method: Assume Poisson statistics N=number of tracks/pad m =mean number of tracks/pad The numbers of empty and occupied pads determine the occupancy as a function of h,b

  11. Energy Loss  Multiplicity 300 mm Si Energy deposited in ith pad (truncated) corrected for angle of incidence Mean energy loss for one particle traversing pad RATIO OF TOTAL TRACKS TO PRIMARY TRACKS 0.30 - 0.40 • Measured S/N = 10 - 20 << Landau Width • Use Non-Hit pads - for • Common-Mode Noise Suppression • M = 240 ± 15 ± 5 ± CMN for one sensor (120 channels) at h = 0

  12. Best estimate  event plane Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Elliptic Flow Fourier decomposition of the Azimuthal Multiplicity Distribution: dN/d(f -YR ) = N0 (1 + 2V1cos (f-YR) + 2V2cos (2(f-YR) + ... ) Directed flow Elliptic flow (reaction plane: YR) View along beamline • V2 = < cos (2(f-Y2)) > / ( <cos(2(Y2a- Y2b))> )1/2

  13. Centrality Determination

  14. NPart and NColl (Au+Au) Paddle Mean NPart

  15. NPart and Ncoll (d+Au) HIJING Simulation Counts dN/dh Pseudorapidity Multiplicity Distribution • Glauber Calculation • Hijing 1.383 • Hulthen w.f. • 41mb inelastic cross-section • Full GEANT Simulation

  16. The Data d+Au Also pp at 200 GeV Au+Au at 62.4 GeV/u Spectra – Talk by Adam Trzupek Au+Au

  17. Models prior to RHIC PRL 85, 3100 (2000) PRL 88, 22302 (2002) PRL 91, 052303 (2003) arXiv:nucl-ex/0405027 Particle Density near Mid-Rapidity On the low side of nearly all predictions

  18. Energy per Unit Volume Number of Particles Produced at y=0 <E> ~ 0.7 GeV dNch/dh Therefore total energy released in |h| < 1 is ~2000GeV Energy of Collision “Relevant” Initial Volume ~ R2 ( 1 fm)  2 Initially released Energy per Unit Volume  5 GeV/fm3 Note: Energy Density inside Proton ≈ 0.5 GeV/fm3 Data from: PRL 85, 3100 (2000); PRL 88, 22302 (2002); PRL 91, 052303 (2003); arXiv:nucl-ex/0405027

  19. The Energy Density is High (3-5 GeV/fm3)andMuch Larger than Inside a HadronA Description in Terms of Hadronic Degrees of Freedom is Inappropriate

  20. Baryon Free at Mid-Rapidity PRC 67, 021901R (2003)

  21. 200 GeV Au+Au PHOBOS preliminary 0 < h < 1.5 0-55% central, h+ + h- Evidence from Flow Approaches Hydro Limit PRL,89, 222301 (2002) Nucl. Phys.A715, 611c (2003)

  22. Evidence from Low pT Particles In a large volume, weakly interacting system we would expect the development of particles with long wavelength PHOBOS PHENIX arXiv:nucl-ex/0401006

  23. Suppression of High-pT Particles PHOBOS d+Au 200 GeV Au+Au 0-6% 200 GeV PRL 91, 072302 (2003)

  24. The System is Strongly InteractingatEarly Times (2fm/c)

  25. PHOBOS E895 E895 E895 3.0 GeV Au+Au NA49 BRAHMS prel. NA49 3.6 GeVAu+Au 4.1 GeVAu+Au 200 GeVAu+Au 8.8 GeVPb+Pb 17.3 GeVPb+Pb No Plateau in Rapidity Distributions Plateau in Pseudorapidity Distributions is Misleading Rapidity Distributions of Pions are Gaussian PRL 91, 052303 (2003) arXiv:nucl-ex/0403050

  26. No Boost-Invariant Plateau for v2 PHOBOS Preliminaryv2200 PHOBOSv2130 PRL 89, 222301 (2002)

  27. Limiting Fragmentation in pp

  28. 6% central dNch/dh ¢/<Npart>/2 Au+Au Scaling – Limiting Fragmentation PRL 91, 052303 (2003)

  29. PHOBOS A Rest Frame p or d Rest Frame arXiv:nucl-ex/0403033

  30. Dependence of v2 on sNN and  Submitted to PRL arXiv:nucl-ex 0406021

  31. Limiting Fragmentation in v2 Submitted to PRL arXiv:nucl-ex 0406021

  32. Longitudinal Scaling • Originally expected boost-invariance in mid-rapidity region not observed. • Scaling in fragmentation region seen in Au+Au, d+Au and (previously) in pp and p+A

  33. Connection between Central and Fragmentation Regions PHOBOS PRL 91, 052303 (2003) Nucl.Phys. A715 (2003) 65-74

  34. How to Compare Au+Au, p+p, and d+Au Brenner et al In pp collisions, on average, approximately half the energy goes into the leading baryon A.Brenner et al.Phys.Rev.D26 (1982)1497l arXiv:nucl-ex/0301017 arXiv:nucl-ex/0403033 Au+Au higher than pp and d+Au. But……..

  35. arXiv:nucl-ex/0301017 Universal Curve for Nch vs (s) When pp corrected for leading baryon

  36. Npart scaling for: pA, KA, pA, dA, AA 10 GeV to 200 GeV Npart from 2 to 350 Preliminary pp chosen to have the same available energy Phobos and E178 data E178: J.E.Elias et al., Phys.Rev.D22(1980) 13 arXiv:nucl-ex/0403033

  37. NPart Scaling of Total Particle Production – Independent of Nature of Collision System

  38. Factorization of Energy and Centrality Dependence PRC 70 (2004) 021902R Where are the Minijets?

  39. Centrality Dependence of d+Au arXiv:nucl-ex/0403033

  40. Factorization into Geometric and Energy Parts SAME SEEN IN p+A AT ENERGIES 50-200 GeV arXiv:nucl-ex/0403033

  41. Energy and Geometry Factorize – Independent of pT 62.4 GeV 200 GeV PHOBOS arXiv:nucl-ex/0405003

  42. The PHOBOS Perspective on Discoveries at RHIC The PHOBOS White Paper nucl-ex/0410022 Summary and Conclusions • High Energy Density Strongly Interacting Matter – Description in Terms of Simple Hadronic Degrees of Freedom Inappropriate. ( No Direct Evidence of Color Deconfinement or Partonic d.o.f) • The Matter is Strongly Interacting – Not the Weakly Coupled QGP Originally Envisioned • Simple Scaling Rules Unite the Data. Suggest Global Constraints or Universality

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