1. Rapidity Dependence of Pion Elliptic Flow Hironori Ito 1 Erik Johnson 2 Steve Sanders 2 BRAHMS Collaboration 1 Brookhaven National Laboratory 2 University of Kansas

2. BRAHMS Collaboration I.Arsene, I.G. Bearden 7, D. Beavis 1, S.Bekele 11, C. Besliu 10, B. Budick 6, H. Bøggild 7, C. Chasman 1, C. H. Christensen 7, P. Christiansen 7, R.Clarke 10, R. Debbe 1,J. J. Gaardhøje, K. Hagel 8, H. Ito 1, A. Jipa 10, J. I. Jordre 10, F. Jundt 2, E.B.Johnson 11, J.I.Jordre 9, C.Jørgensen 7, R. Karabowicz 3, E. J. Kim 11, T.M. Larsen 7, J. H. Lee 1, Y. K.Lee 5, S.Lindal 12, G. Løvhøjden 2, Z. Majka 3, M. Murray 11, J. Natowitz 8, B.S.Nielsen 7, D.Ouerdane 7, R.Planeta 4, F. Rami 2, C.Ristea 7, O.Ristea 10, D. Röhrich 9, B. H. Samset 12, S. J. Sanders 11, R.A.Sheetz 1, P. Staszel 3, T.S. Tveter 12, F.Videbæk 1, R. Wada 8, H.Yang 9, Z. Yin 9, and I. S. Zgura 10 1 Brookhaven National Laboratory, USA, 2 IReS and Université Louis Pasteur, Strasbourg, France 3 Jagiellonian University, Cracow, Poland, 4 Institute of Nuclear Physics, Cracow, Poland, 5 Johns Hopkins University, Baltimore, USA, 6 New York University, USA, 7 Niels Bohr Institute, University of Copenhagen, Denmark, 8 Texas A&M University, College Station. USA, 9 University of Bergen, Norway, 10 University of Bucharest, Romania, 11 University of Kansas, Lawrence,USA, 12 University of Oslo Norway

3. BRAHMS Detector Setup Event plane detectors PID detectors

4. Event Plane Detectors Flow Ring 2 Si Ring 1 Tile Ring 1 Flow Ring 3 ● Flow Ring 2 (silicon strips): ● 42 segments per 2π ● -2 < η < 0.2 ● Flow Ring 3 (silicon strips): ● 42 segments per 2π ● -2 < η < 1.2 ● Si Ring 1 (silicon strips): ● 6 segments per 2π ● -2.4 < η < 0.8 ● Tile Ring 1 (scintillator tile): ● 6 segments per 2π ● -2 < η < -0.8

5. Introduction to Flow φ Initial spatial anisotropy......final momentum anisotropy...after rescattering leads to... Elliptic Flow: n = 2

6. Rapidity Dependence? Current Status PHOBOS and STAR have measured p T integrated v 2 over a wide pseudorapidity range. →p T integrated v 2 has strong pseudorapidity dependence. Charged Hadron STAR also measured charged hadron v 2 (p T ) at forward rapidity, and find a large p T dependence.

7. Method a,b and c are the Scintillator Tile, the Silicon Strip and the Beam-Beam counters Methods describe by A. M. Poskanzer and S. A. Voloshin Phys. Rev. C58 (1998) 1671 Nth order event plane Observed v 2 Event plane resolution correction Real v 2

8. Particle Identification at Midrapidity Time-of-Flight Identification ● Pions: 2.5 GeV/c ● Protons:4 GeV/c ● Kaons: 2 GeV/c

9. Particle Identification at Forward Rapidity RICH identification ● Pions:28 GeV/c ● Protons: 35 GeV/c ● Kaons: 28 GeV/c

10. Charged Hadron Errors are statistical only 10-20% Central Charged Hadron V 2 at Midrapidity Strong p T dependence is seen at midrapidity. 10-20% Central Errors are statistical only

11. Pion V 2 at Midrapidity Errors are statistical only 10-20% central events...pion v 2 (p T ) is also consistent with STAR data. Error is statistical only 10-20% central events

12. Find strong p t dependence Pion Error is statistical only η = 3.2 Pion V 2 at Forward Rapidity Pion Errors are statistical only η = 0 Pions Error is statistical only η = 3.2 Pion elliptic flow at forward rapidity is very smilar to that at midrapidity. 10-20%

13. η = 1 η = 3.2 η = 0 Rapidity Dependence Small η dependence found. η = 0 η = 1 η = 3.2 3D Hydro (Hirano) 3D Hydrodynamic calculation also shows a very small pseudorapidity dependence. Charged hadrons

14. p T Integrated v 2 Integrated v 2 are derived using the measured spectra and v 2 (p T ). (See a poster by C. Ristea.) Integrated v 2 are also relatively flat. GeV/c 00.55 10.53 2. h+ 0.506 h- 0.423 η = 0 η = 1 η = 3.2 3D Hydro (Hirano)

15. Centrality Dependence Large centrality dependence is seen for p T integrated v 2 — consistant with PHOBOS results. Centrality dependence at midrapidity

16. Conclusion ● v 2 (p T ) for charged hadrons and pions have been measured at midrapidity as well as at forward rapidity. ● v 2 (p T ) shows small pseudorapidity dependence—consistent with 3D Hydro model. ● η dependence of p T integrated v 2 is strongly sensitive to measured spectra. ● Strong centrality dependence observed. Proton and Kaon results are forthcoming.