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Inkyu Park University of Rochester For the PHOBOS Collaboration

Measurements of charged particle multiplicity and elliptic flow in wide range of pseudo-rapidity with the PHOBOS detector. Inkyu Park University of Rochester For the PHOBOS Collaboration. PHOBOS Collaboration. ARGONNE NATIONAL LABORATORY Birger Back, Alan Wuosmaa

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Inkyu Park University of Rochester For the PHOBOS Collaboration

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  1. Measurements of charged particle multiplicity and elliptic flow in wide range of pseudo-rapiditywith the PHOBOS detector Inkyu Park University of Rochester For the PHOBOS Collaboration

  2. PHOBOS Collaboration ARGONNE NATIONAL LABORATORYBirger Back, Alan Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Nigel George, Stephen Gushue, George Heintzelman, Burt Holzman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov INSTITUTE OF NUCLEAR PHYSICS, KRAKOWAndrzej Budzanowski, Roman Hołyński, Jerzy Michałowski, Andrzej Olszewski, Pawel Sawicki, Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Woźniak MASSACHUSETTS INSTITUTE OF TECHNOLOGYMaartin Ballintijn, Wit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Jang Woo Lee, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Carla Vale, Gerrit van Nieuwenhuizen, Gábor Veres, Robin Verdier, Bernard Wadsworth, Bolek Wysłouch NATIONAL CENTRAL UNIVERSITY, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo García, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey, Marguerite Belt Tonjes UNIVERSITY OF ROCHESTERJoshua Hamblen, Erik Johnson, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs Transverse Dynamics at RHIC

  3. PHOBOS detector 137000 Silicon Pad Channels Spectrometer PID 1m Ring Counters Octagon Trigger & centrality Paddle counter Nearly 4pCoverage Transverse Dynamics at RHIC

  4. f h= -5.4 -3 0 +3 +5.4 How we measure Nch & Flow? RingsN Octagon RingsP • Nch, dN/dh All we have to do is to count hits carefully (doesn’t mean it’s easy) • Flow Make sub-event, and reconstruct event axis using hits, then get sub-event correlation Transverse Dynamics at RHIC

  5. Contents of this talk • Variables • Total charged multiplicity, Nch • dN/dh (|h|<5.4) • Elliptic flow : v2(h) Ä • Collision • energy (ÖS) • centrality (Npart) • system (ee, pp, AA) Transverse Dynamics at RHIC

  6. Section I : Nch Transverse Dynamics at RHIC

  7. Maximum Nch : Head-on collision How many particles are created at RHIC? PHOBOS exclusive 4p measurement, least biased result @RHIC For head-on collisions (0%-6%) *nucl-ex/0210015 Transverse Dynamics at RHIC

  8. How about Centrality dependence? Systematic errors not shown Transverse Dynamics at RHIC

  9. Slopes = <Nch> in e+ e- collision! Nch nicely scales with Npart Au+Au *nucle-ex/0301017 Transverse Dynamics at RHIC

  10. Universality of Total Multiplicity? for pp • pQCD e+e- Calculation (A.Mueller,1983) Same for all systems at same s(seff for pp), except low energy AA Transverse Dynamics at RHIC

  11. To see better e+e- PHOBOS Central Au+Au e+e- pp (pp) data @ seff Central AA Different systems converge at high energy. *nucl-ex/0301017 1 10 102 103 s (GeV) Transverse Dynamics at RHIC

  12. Even the shape is similar! 200 GeV e+e- measures dN/dyT(rapidity relative to“thrust” axis) Transverse Dynamics at RHIC

  13. Section II : dN/dh Transverse Dynamics at RHIC

  14. “Boost invariant” “Fragmentation” dN/dh @ h= 0 h = 0 dN/dh( Centrality,s ) *nucle-ex/0210015 200 GeV 19.6 GeV 130 GeV PHOBOS PHOBOS PHOBOS dN/dh Typical systematic band (90%C.L.) h Naïve expectation  broadening of plateau  Boost invariance Transverse Dynamics at RHIC

  15. dNch/dh ¢/<Npart/2> 6% central PHOBOS Au+Au Systematic errors not shown ybeam ybeam Close look : Head-on collision case *nucle-ex/0210015 PHOBOS Au+Au dNch/dh 6% central “broadening of plateau” is limited, while “fragmentation region” grows with sNN, universal limiting curve? Transverse Dynamics at RHIC

  16. Limiting curve in other systems : pp, e+e-, PLB459 (1999) dN/dh¢ UA5, Z.Phys.C33, 1 (1986) xF scale Liminting curve does exist in e+e- as well in pp Transverse Dynamics at RHIC

  17. Only for head-on collisions? Limiting curve does exist for each centrality. Q: Is Limiting curve independent of centrality? *nucle-ex/0210015 Transverse Dynamics at RHIC

  18. 200 GeV 130 GeV dN/dh/Npart/2 19.6 GeV 200 GeV 0-6% central 35-40% central 19.6 GeV Close Look: Centrality Dependence Limiting curve shape changes with centrality Brahms % Brahms has no 20GeV data. “Universal limiting curve in both centrality and energy”, I.G. Bearden et al., Phys. Lett. B523, 227 (2001) *nucle-ex/0210015 Transverse Dynamics at RHIC

  19. Section III : Flow dN/dh Transverse Dynamics at RHIC

  20. Thoughts on LDL, Hydro. • LDL (Low Density Limit) •  very little re-scattering • v2 µ e x (dN/dy)(anisotropy, density) • Geometry : same for all AGS, SPS, RHIC •  Only multiplicity dependence left • Hydro Limit •  Full thermalization by re-scattering • No more “density” dependence, Pt dependence • v2µ e, suggest linear function with “b” Transverse Dynamics at RHIC

  21. Already have an answer? LDL doesn’t have any Pt dependent calculation, while Hydro naturally include Pt dependence as v2µ Pt 0<h<1.5 Good agreement with STAR, PHENIX results 200GeV preliminary Transverse Dynamics at RHIC

  22. 0.1 midrapidity : |h| < 1.0 Hydrodynamic model Hydro Preliminary V2 LDL No collective motion centrality What we expect in Mid-rapidity v2 µ e v2µ e (dN/dy) Transverse Dynamics at RHIC

  23. Preliminary v2200 Final v2130 PHOBOS v2(cen) Little energy dependence, linear dependence on centrality 200 |h|<1 130 Good agreement with STAR Transverse Dynamics at RHIC

  24. Preliminaryv2200 Final v2130 How about h dependence? Naïve expectation  Boost invariance 200 130 <Npart>~200 Transverse Dynamics at RHIC

  25. 40-43GeV/fm3 E0(t=0.6) hs 3D-Hydro calculation Not a trivial job: function of initial conditions (eg, E0) Modeling of Initial Energy density function E0(h,x,y) Dhflat + Dhgaus *nucl-th/0108004 (Long boost inv.) (short boost inv.) Both reproduce dN/dh, T. Hirano, Nucl/th0108004 Transverse Dynamics at RHIC

  26. You may wonder anyway… dN/dh@Npart~200 Arbitrary fit Fit highh dN/dh is broader than v2 v2µ PT Missing measurement <PT>(h) Transverse Dynamics at RHIC

  27. Conclusion • Nch(total) (centrality, collision energy) • Universality in e+e-, pp, AA • dN/dh (centrality, collision energy) • broad region of limiting fragmentation observed • limiting fragmentation curve is centrality dependent • v2(cen), v2(PT) prefer Hydro picture • v2(h) rules out “broad boost invariant region” • no clear theoretical explanation • Longitudinal boost invariance was a naïve assumption Transverse Dynamics at RHIC

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