1. June 18, 2004BNL - Elliptic Flow, S. Manly1 Au-Au event in the PHOBOS detector Energy dependence of elliptic flow over a large pseudorapidity range in Au+Au collisions at RHIC Steven Manly University of Rochester Representing the PHOBOS Collaboration

2. June 18, 2004BNL - Elliptic Flow, S. Manly2 Collaboration meeting, BNL October 2002 Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley, Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski, Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Adam Harrington, Michael Hauer, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Helen Seals, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch ARGONNE NATIONAL LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER

3. June 18, 2004BNL - Elliptic Flow, S. Manly3 “Flow” = patterns in the energy, momentum, or particle density distributions that we use to ferret out clues as to the nature of the collision/matter To what extent is the initial geometric asymmetry mapped into the final state? View along beamline

4. June 18, 2004BNL - Elliptic Flow, S. Manly4 Flow as an experimental probe  Sensitive to interaction strength  Sensitive to very early times and particle velocities since asymmetry disappears with time  With sufficient  coverage, it probes longitudinal uniformity of system View along beamline

5. June 18, 2004BNL - Elliptic Flow, S. Manly5 (reaction plane) Flow quantified dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) View along beamline Fourier decomposition of the azimuthal multiplicity distribution Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Best estimate  event plane

6. June 18, 2004BNL - Elliptic Flow, S. Manly6 (reaction plane) dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) Directed flow Flow quantified View from above View along beamline

7. June 18, 2004BNL - Elliptic Flow, S. Manly7 (reaction plane) dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) Elliptic flow Flow quantified View along beamline

8. June 18, 2004BNL - Elliptic Flow, S. Manly8 (reaction plane) dN/d(  R ) = N 0 (1 + 2V 1 cos (  R ) + 2V 2 cos (2(  R ) +... ) Higher terms Flow quantified View along beamline

9. June 18, 2004BNL - Elliptic Flow, S. Manly9 b (reaction plane) View along beamline n=2, elliptic flow

10. June 18, 2004BNL - Elliptic Flow, S. Manly10 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) |  |<1 (PHOBOS : Normalized Paddle Signal) Hydrodynamic limit STAR: PRL86 (2001) 402 PHOBOS preliminary Hydrodynamic limit STAR: PRL86 (2001) 402 PHOBOS preliminary Thanks to M. Kaneta

11. June 18, 2004BNL - Elliptic Flow, S. Manly11 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro PRL 91 (2003) 182301

12. June 18, 2004BNL - Elliptic Flow, S. Manly12 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T STAR 130 GeV 4-cumulant STAR 130 GeV 2-cumulant STAR 130 GeV Reaction Plane 5-53% central Preliminary PHOBOS 200 GeV 0-55% central p T (GeV/c) v2v2 Preliminary

13. June 18, 2004BNL - Elliptic Flow, S. Manly13 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T Xhangbu Xu, Quark Matter 2004 nucl-ex/0306007

14. June 18, 2004BNL - Elliptic Flow, S. Manly14 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference Elliptic flow falls off sharply as a function of |  | T.Hirano, K.Tsuda, PRC66,054905(2002).

15. June 18, 2004BNL - Elliptic Flow, S. Manly15 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference Elliptic flow falls off sharply as a function of |  | n  2 terms observed

16. June 18, 2004BNL - Elliptic Flow, S. Manly16 Flow at RHIC to date (a few highlights) Elliptic flow is large near  =0 (relative to hydro limit) V 2 (p T ) grows with p T at low p T, consistent with hydro V 2 (p T ) saturates at high p T Partonic energy loss plus quark coalescence may explain saturation and meson-baryon difference Elliptic flow falls off sharply as a function of |  | n  2 terms observed Strongly interacting dense matter! Partonic? Longitudinal structure of the collision not trivially understood Systematic study of v2(E,  ) probes the longitudinal dynamics of the collision This work 

17. June 18, 2004BNL - Elliptic Flow, S. Manly17 Flow in PHOBOS

18. June 18, 2004BNL - Elliptic Flow, S. Manly18 Large  coverage Data at 19.6, 62.4, 130 and 200 GeV 1m 2m 5m 01234512345  coverage for vtx at z=0

19. June 18, 2004BNL - Elliptic Flow, S. Manly19  Subevent technique: correlate event plane in one part of detector to  asymmetry in track pattern in other part of detector  Correct for imperfect reaction plane resolution -2.0 <  < -0.1 SubE (a)SubE (b) nana nbnb 0.1 <  < 2.0  dependence of the multiplicity Flow: basic method

20. June 18, 2004BNL - Elliptic Flow, S. Manly20 Pixelized detector Pixelized detector Hit saturation, grows with occupancy Sensitivity to flow reduced Can correct using analog energy deposition –or- measure of occupied and unoccupied pads in local region assuming Poisson statistics

21. June 18, 2004BNL - Elliptic Flow, S. Manly21  z Dilutes the flow signal  Remove Background  Estimate from MC and correct flow signal Azimuthally symmetric background + Azimuthally symmetric backgrounds Azimuthally symmetric backgrounds

22. June 18, 2004BNL - Elliptic Flow, S. Manly22 Background suppression Works well in Octagon  dE (keV) cosh  Background! Technique does not work in rings because angle of incidence is ~90  Beampipe Detector Demand energy deposition be consistent with angle

23. June 18, 2004BNL - Elliptic Flow, S. Manly23   RingsN OctagonRingsP Spec holes Vtx holes

24. June 18, 2004BNL - Elliptic Flow, S. Manly24   RingsN OctagonRingsP Hit-based method Vertex range -10<z<10 Subevents for reaction plane evaluation

25. June 18, 2004BNL - Elliptic Flow, S. Manly25 Flow: method continued Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Determine event plane in each subevent,  2 ±   RingsN OctagonRingsP

26. June 18, 2004BNL - Elliptic Flow, S. Manly26 Flow: method continued   RingsN OctagonRingsP Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Correlate  2 ± with hits outside of given subevent to get raw v 2

27. June 18, 2004BNL - Elliptic Flow, S. Manly27 Flow: method continued Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Determine event plane resolution by correlating  2 + and  2 -   RingsN OctagonRingsP

28. June 18, 2004BNL - Elliptic Flow, S. Manly28 Flow: method continued Method from Poskanzer and Voloshin, Phys. Rev. C58 (1998) 1671 Correct raw v 2 by resolution (factor of 1.7 to 3 depending on energy and centrality, well understood) Correction determined from data   RingsN OctagonRingsP

29. June 18, 2004BNL - Elliptic Flow, S. Manly29 Flow: method continued Resolution-corrected v 2 is further corrected by ~30%  dilution due to azimuthally symmetric background  effects due to residual bias in  2 ± due to hole filling Correction derived from Monte Carlo   RingsN OctagonRingsP

30. June 18, 2004BNL - Elliptic Flow, S. Manly30 Flow: method continued Have agreement between:  Two hit-based analyses  one “holy”, one not  Track-based analysis with NO background   RingsN OctagonRingsP

31. June 18, 2004BNL - Elliptic Flow, S. Manly31 v 2 vs.  (four energies) (0-40% central Au+Au data) Bars are 1  “statistical” errors, expect some correlation

32. June 18, 2004BNL - Elliptic Flow, S. Manly32 v 2 vs.  (four energies) (0-40% central Au+Au data) Boxes are 90% C.L. systematic errors

33. June 18, 2004BNL - Elliptic Flow, S. Manly33 v 2 vs.  (four energies) (0-40% central Au+Au data) Shape is triangular at all four energies, no evidence of plateau

34. June 18, 2004BNL - Elliptic Flow, S. Manly34 v 2 vs.  (four energies) (0-40% central Au+Au data) Drop highest |  | points at 19.6 GeV in following results

35. June 18, 2004BNL - Elliptic Flow, S. Manly35 Systematic errors Hit definition Beam orbit/alignment Subevent definition Transverse vertex position cut Bins for weighting matrix definition Dead channel correction algorithm Poisson occupancy correction algorithm Hole filling alogorithm Knowledge of azimuthally symmetric background dN/d  shape Symmetry in 

36. June 18, 2004BNL - Elliptic Flow, S. Manly36 v 2 vs.  (four energy overlay) Only statistical errors shown Preliminary Au+Au data (0-40% central)

37. June 18, 2004BNL - Elliptic Flow, S. Manly37 Evolution of v 2 with energy Preliminary Au+Au data (0-40% central)

38. June 18, 2004BNL - Elliptic Flow, S. Manly38 Take out differing beam boosts by going into approximate frame of reference of target Look at  ’ scaling Limiting fragmentation PHOBOS Au+Au results PRL 91, 052303 (2003) “limiting fragmentation”  energy independence in  ’=|  |-y beam

39. June 18, 2004BNL - Elliptic Flow, S. Manly39 y vs.  Boost invariant spectra transform as: Jacobian suppresses spectra at low , low p T, and for large mass

40. June 18, 2004BNL - Elliptic Flow, S. Manly40 y vs.  : effect on multiplicity dN/d  dN/dy 0

41. June 18, 2004BNL - Elliptic Flow, S. Manly41 Near mid-rapidity, integration over p T weights flow to higher p T due to suppression at low p T  v 2 (  ) larger than v 2 (y) P. Kolb, Proc. of 17 th Winter Workshop on Nuclear Dynamics (2001) y vs.  : effect on v 2

42. June 18, 2004BNL - Elliptic Flow, S. Manly42 y vs.  : effect on v 2 0 V2()V2() V 2 (y) No change in the qualitative features of the result (<15% at  =0)

43. June 18, 2004BNL - Elliptic Flow, S. Manly43 Limiting fragmentation and elliptic flow Only statistical errors shown Preliminary Au+Au data (0-40% central)

44. June 18, 2004BNL - Elliptic Flow, S. Manly44 Limiting fragmentation and elliptic flow Only statistical errors shown Preliminary Au+Au data (0-40% central)  ’=|  |-ybeam

45. June 18, 2004BNL - Elliptic Flow, S. Manly45 Conclusions No boost invariant plateau over a broad region of |  |

46. June 18, 2004BNL - Elliptic Flow, S. Manly46 Conclusions No boost invariant plateau over a broad region of |  | Linear logarithmic growth with center-of-mass energy in differing regions of |  | Preliminary Au+Au data (0-40% central)

47. June 18, 2004BNL - Elliptic Flow, S. Manly47 Preliminary Au+Au data (0-40% central) Conclusions No boost invariant plateau over a broad region of |  | Linear logarithmic growth with center-of-mass energy in differing regions of |  | No sharp changes in the dynamics of particle production in pseudorapidity or beam energy Preliminary Au+Au data

48. June 18, 2004BNL - Elliptic Flow, S. Manly48 Conclusions No boost invariant plateau over a broad region of |  | Linear logarithmic growth with center-of-mass energy in differing regions of |  | Preliminary Au+Au data Preliminary Au+Au data (0-40% central) No sharp changes in the dynamics of particle production in pseudorapidity or beam energy

49. June 18, 2004BNL - Elliptic Flow, S. Manly49 Au-Au event in the PHOBOS detector