Rapidity Dependence of Pion Elliptic Flow

1
Rapidity Dependence of Pion Elliptic Flow
Hironori Ito1 Erik Johnson2 Steve Sanders2
1Brookhaven National Laboratory 2University of
Kansas
BRAHMS Collaboration
2
BRAHMS Collaboration

• I.Arsene, I.G. Bearden7, D. Beavis1, S.Bekele11,
  C. Besliu10, B. Budick6,
• H. Bøggild7, C. Chasman1, C. H. Christensen7, P.
  Christiansen7, R.Clarke10,
• R. Debbe1,J. J. Gaardhøje, K. Hagel8, H. Ito1, A.
  Jipa10, J. I. Jordre10, F. Jundt2,
  E.B.Johnson11, J.I.Jordre9, C.Jørgensen7, R.
  Karabowicz3, E. J. Kim11,
• T.M. Larsen7, J. H. Lee1, Y. K.Lee5,
  S.Lindal12, G. Løvhøjden2, Z. Majka3,
• M. Murray11, J. Natowitz8, B.S.Nielsen7,
  D.Ouerdane7, R.Planeta4, F. Rami2, C.Ristea7,
  O.Ristea10, D. Röhrich9, B. H. Samset12, S. J.
  Sanders11, R.A.Sheetz1, P. Staszel3, T.S.
  Tveter12, F.Videbæk1, R. Wada8, H.Yang9, Z. Yin9,
  and I. S. Zgura10
• 1Brookhaven National Laboratory, USA, 2IReS and
  Université Louis Pasteur, Strasbourg, France
  3Jagiellonian University, Cracow, Poland,
  4Institute of Nuclear Physics, Cracow, Poland,
  5Johns Hopkins University, Baltimore, USA, 6New
  York University, USA, 7Niels Bohr Institute,
  University of Copenhagen, Denmark, 8Texas AM
  University, College Station. USA, 9University of
  Bergen, Norway, 10University of Bucharest,
  Romania, 11University of Kansas, Lawrence,USA,12
  University of Oslo Norway

3
BRAHMS Detector Setup
4
Event Plane Detectors

• Flow Ring 2 (silicon strips)
• 42 segments per 2p
• -2 lt ? lt 0.2
• Flow Ring 3 (silicon strips)
• 42 segments per 2p
• -2 lt ? lt 1.2
• Si Ring 1 (silicon strips)
• 6 segments per 2p
• -2.4 lt ? lt 0.8
• Tile Ring 1 (scintillator tile)
• 6 segments per 2p
• -2 lt ? lt -0.8

Flow Ring 3
Si Ring 1
Flow Ring 2
Tile Ring 1
5
Introduction to Flow
Initial spatial anisotropy...
...final momentum anisotropy
...after rescattering leads to ...
Elliptic Flow n 2
6
Rapidity Dependence?Current Status
7
Method
Nth order event plane
Methods describe by A. M. Poskanzer and S. A.
Voloshin Phys. Rev. C58 (1998) 1671
Event plane resolution correction
Observed v2
Real v2
a,b and c are the Scintillator Tile, the Silicon
Strip and the Beam-Beam counters
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
• Pions28 GeV/c
• Protons 35 GeV/c
• Kaons 28 GeV/c

10
Charged Hadron V2 at Midrapidity
Strong pT dependence is seen at midrapidity.
11
Pion V2 at Midrapidity
12
Pion V2 at Forward Rapidity
? 3.2
10-20
Find strong pt dependence
Pion Error is statistical only
13
Rapidity Dependence
Small ? dependence found.
Charged hadrons
? 0
? 1
? 3.2
14
pT Integrated v2
Integrated v2 are derived using the measured
spectra and v2(pT). (See a poster by C.
Ristea.) Integrated v2 are also relatively
flat. lt?gt ltpTgt GeV/c 0 0.55 1 0.53
2. h 0.506 h- 0.423

15
Centrality Dependence
Centrality dependence at midrapidity
Large centrality dependence is seen for pT
integrated v2 consistant with PHOBOS results.
16
Conclusion

• v2(pT) for charged hadrons and pions have been
  measured at midrapidity as well as at forward
  rapidity.
• v2(pT) shows small pseudorapidity
  dependenceconsistent with 3D Hydro model.
• ? dependence of pT integrated v2 is strongly
  sensitive to measured spectra.
• Strong centrality dependence observed.
• Proton and Kaon results are forthcoming.