Rapidity Dependence of Pion Elliptic Flow

Hironori Ito1

Erik Johnson2

Steve Sanders2

BRAHMS Collaboration

1Brookhaven National Laboratory2University of Kansas

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 A&M University, College Station. USA, 9University of

Bergen, Norway, 10University of Bucharest, Romania, 11University of Kansas, Lawrence,USA,12 University of Oslo

Norway

BRAHMS Detector Setup

Event planedetectors

PID detectors

Event Plane Detectors

Flow Ring 2Si 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

Introduction to Flow

φ

Initial spatial anisotropy... ...final momentum anisotropy

...after rescatteringleads to ...

Elliptic Flow: n = 2

Rapidity Dependence?Current Status

PHOBOS and STAR have measured p

T

integrated v2

over a wide pseudorapidity range.

→pT integrated

v2 has strong

pseudorapidity dependence.

Charged Hadron

STAR also measured charged hadron v

2(p

T) at forward rapidity, and find a large

pT dependence.

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. VoloshinPhys. Rev. C58 (1998) 1671

Nth order event plane

Observed v2

Event plane resolution correction

Real v2

Particle Identification at Midrapidity

Time-of-Flight Identification● Pions: 2.5 GeV/c● Protons: 4 GeV/c● Kaons: 2 GeV/c

Particle Identification at Forward Rapidity

RICH identification● Pions:28 GeV/c● Protons: 35 GeV/c● Kaons: 28 GeV/c

Charged HadronErrors are statistical only

10-20% Central

Charged Hadron V2 at Midrapidity

Strong pT

dependence is seen at midrapidity.

10-20% Central

Errors are statistical only

Pion V2 at Midrapidity

Errors are statistical only

10-20% central events ...pion v2(p

T) is

also consistent with STAR data.

Error is statistical only

10-20% central events

Find strong pt dependence

PionError is statistical only

η = 3.2

Pion V2 at Forward Rapidity

PionErrors are statistical only

η = 0

PionsError is statistical only

η = 3.2

Pion elliptic flow at forward rapidity is very smilar to that at midrapidity.

10-20%

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

Charged hadrons

pT Integrated v

2

Integrated v2 are derived

using the measured spectra and v

2(p

T). (See

a poster by C. Ristea.)

Integrated v2 are also

relatively flat.

<η> <pT> GeV/c

0 0.55 1 0.53 2. h+ 0.506 h- 0.423

η = 0

η = 1

η = 3.2

3D Hydro(Hirano)

Centrality Dependence

Large centrality dependence is seen for p

T

integrated v2 —

consistant with PHOBOS results.

Centrality dependence at midrapidity

Conclusion

● v2(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.