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Latest PHOBOS Results Bjorken is AWOL! Mark D. Baker (BNL) for the Collaboration

Latest PHOBOS Results Bjorken is AWOL! Mark D. Baker (BNL) for the Collaboration. Phobos data on dN/d h New Phobos data on dN/d h Particle production in pp&AA collisions The source isn’t boost invariant dN/d h may teach us about QCD. The PHOBOS Collaboration.

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Latest PHOBOS Results Bjorken is AWOL! Mark D. Baker (BNL) for the Collaboration

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  1. Latest PHOBOS Results Bjorken is AWOL!Mark D. Baker(BNL)for the Collaboration Phobos data on dN/dh New Phobos data on dN/dh Particle production in pp&AA collisions • The source isn’t boost invariant • dN/dh may teach us about QCD Mark D. Baker

  2. The PHOBOS Collaboration Birger Back, Alan Wuosmaa Mark Baker, Donald Barton, Alan Carroll, Nigel George, Stephen Gushue, George Heintzelman, Burt Holzman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov Andrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak Wit Busza (Spokesperson),Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane , Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch Chia Ming Kuo, Willis Lin, Jaw-Luen Tang Joshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly,Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs Russell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer Richard Bindel, Alice Mignerey ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ROCHESTER UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND Mark D. Baker

  3. What do I mean “Bjorken”? Boost-invariant Increasing E y y dN/dy’ “Inside-out” & 1 dimensional 0 y’=y-ybeam Mark D. Baker

  4. Impact of “Bjorken” X • dN/dy distribution is flat over a large region except “near the target”. • v2 is independent of y over a large region except “near the target”. (2d-hydro.) • pT(y) described by 1d or 2d-hydro. • Usual HBT interpretation starts from a boost-invariant source. • T(t) described by 1d-hydro. • Simple energy density formula X Mark D. Baker

  5. PHOBOS Apparatus 135,000 Silicon Pad channels 12 meters of Beryllium beampipe Mark D. Baker

  6. PHOBOS Silicon Detector Octagon Detector Vertex Detector Octagon Detector: 2.7 x 8.8 mm2 Vertex Detector: 0.4 x 12 mm2 Ring Counter Mark D. Baker

  7. Many ways to slice pz Rapidity: Generalized velocity Feynman x: scaled pz Pseudorapidity: ~y: easier to measure Away from mid-rapidity: Mark D. Baker

  8. An event in PHOBOS -3 0 +3 -5.5 +5.5 Single Event in PHOBOS Unrolled: tracklets f h Mark D. Baker

  9. PHOBOS results at 200 GeV Theory 1999 Theory 2000 PHOBOS 2001 PHOBOS 2000 PRL 85 (2000) 3100 PRL 88 (2002) 022302 Total Ncharged ~ 5000 particles Mark D. Baker

  10. RHIC results so far PHOBOS, PRL 88 (2002) 022302 Brahms 200 GeVnucl-ex/0112001 Phenix 200 GeVpreliminary Mark D. Baker

  11. Centrality Dependence |h| < 1 PRC 65, 031901(2002) & submitted to PRC Saturation Model Kharzeev,Levin nucl-th/0108006 Peripheral Central Mark D. Baker

  12. Implications: • Particle production on the low side. • Limited entropy production in late stages. • dN/dh is a window to QCD 1 2 3 4 Colliding Nuclei Parton Cascade Hadron Gas & Freeze-out HardCollisions QGP? / Fragmentation Gentle Freeze-out Geometry/Saturation QCD Mark D. Baker

  13. Energy Spectrum (DE) in Si pads 1 hit Data MC 2 hits -3 0 +3 -5.5 +5.5 Analog and Digital Hit-Counting f h Analog: Digital: • Sum energy • Divide by E/particle • Correct for material • Count hits • Correct for multi-hits • Correct for material Mark D. Baker

  14. Latest PHOBOS results Typical Systematic Errors 200 GeV 130 GeV dN/dh dN/dh dN/dh Peripheral h h h dN/dh dN/dh dN/dh Central h h h Mark D. Baker

  15. Collider Kinematics Beam rest frame S’ Lab = cm frame S ybeam -ybeam y’=0 y’=-2ybeam Fragmenting Target p y’>~0 Mark D. Baker

  16. Latest PHOBOS results (vs pp) Results : Limiting Fragmentation UA5, Z.Phys.C33, 1 (1986) p + p inelastic A+A PHOBOS 200 0-6% PHOBOS 130 0-6% EMU-13 17 0-9.4% (different frame) Systematic errors not shown AuAu and pp show the same behavior, the extent of the “fragmentation region” grows with collision energy Mark D. Baker

  17. Centrality dependence. Results : Limiting Fragmentation vs Centrality • Each centrality exhibits limiting fragmentation (E-independence) • but the shape in this region depends on centrality ! 200 GeV 200 GeV 130 GeV 130 GeV Fragmentation Fragmentation Systematic errors not shown 200 GeV Data 130 GeV Data Mark D. Baker

  18. Fragmentation: Energy dependence Low energy ANY High energy Confusion Fragmenting Target For E>Ethresh, dN/dy’(y’~0) reaches a limiting value. Mark D. Baker

  19. Let’s pick a different frame... Beam rest frame S’ Arbitrary frame S’’ y’=-2ybeam y’=0 y’’=+3 y’’=3-2ybeam = Mark D. Baker

  20. Makes sense for pp p etc. Limiting fragmentation could just be local string fragmentation Also works in e+e- But how about AA?? Mark D. Baker

  21. Can we see the “Limit Curves”. UA5, Z.Phys.C33, 1 (1986) A+A p + p inel. Systematic errors not included Line “p” to guide the eye 1.45 x line “p” Systematic errors not shown Mark D. Baker

  22. Boost-invariance vs. Outside-in evolution McLerran, Venugopolan Kharzeev, Nardi, Levin Kovchegov... Mark D. Baker

  23. Can “we” calculate the limit curves? • Saturated initial state gives predictions about final state. • Nh = c x Ng Saturation Model Kharzeev,Levin nucl-th/0108006 Not really designed for frag.region... l~.25 from HERA F2 data Mark D. Baker

  24. Saturation model in h’ space... 900 546 Kharzeev, Levin nucl-th/0108006 (code from P.Steinberg) More work needed... 200 130 53 h’ Mark D. Baker

  25. Results : Energy Dependence & Comparison to pp It’s the central AA that agrees best w/ pp shape !? • Despite: • Hard processes • “stopping” • Rescattering • Saturation Systematic errors not shown Mark D. Baker

  26. Peripheral AA is NOT pp Mark D. Baker

  27. Centrality dependence again. Results : Limiting Fragmentation vs Centrality • Each centrality exhibits limiting fragmentation (E-independence) • but the shape in this region depends on centrality ! 200 GeV 200 GeV 130 GeV 130 GeV Fragmentation Fragmentation Systematic errors not shown 200 GeV Data 130 GeV Data Mark D. Baker

  28. Elliptic Flow: A collective effect Beam’s eye view of a non-central collision: Asymmetric particle distribution: f Particles prefer to be “in-plane” dN/d(f -YR ) = N0 (1 + 2V1cos (f-YR) + 2V2cos (2(f-YR)) + ... ) Elliptic flow Mark D. Baker

  29. Elliptic Flow PRL 86 (2001) 402 Particle asymmetry midrapidity : |h| < 1.0 V2 Hydrodynamic model Preliminary Normalized Multiplicity Central Peripheral Mark D. Baker

  30. Pseudorapidity dependence of V2 V2 Averaged over centrality PHOBOS Preliminary h Errors are statistical only (systematic errors ~ 0.007) Mark D. Baker

  31. Summary • The source is not boost invariant • Limiting “fragmentation” works over a broad & growing region of h’. • Elliptic Flow is strongly dependent on h (y) • AA at 200 GeV is NOT very boost-invariant! • AA vs. pp • Central AA & pp shape very similar (?!) • Peripheral data shows high h excess. • Outlook • Compare AA & pp WELL at a few energies... • QCD understanding of dN/dh’ in AA & pp? Mark D. Baker

  32. For AA: How about boost invariance? = Stronger & different ansatz: global state between two ~irrelevant “black walls” Mark D. Baker

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