Elliptic Flow Analysis at BRAHMS

Hironori Ito

BNL

Charged-particle anisotropy over pseudorapidity and transverse momentum ranges of 0<η<3 and 0<pt<3 in AuAu Collisions at √s_NN = 200 GeV

Current status of BRAHMS elliptic flow analysis

BRAHMS Collaboration

I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J.Brzychczyk4, B. Budick6,

H. Bøggild7 , C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1,

E. Enger12, J. J. Gaardhøje7, M. Germinario7 , K. Grotowski4 , K. Hagel8, O. Hansen7,

A.K. Holme12, H. Ito1, E. Jacobsen7, A. Jipa10, J. I. Jordre10, F. Jundt2, E. Johnson11, C.E.Jørgensen7, R. Karabowicz4 , T. Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12,

J. H. Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3, A. Makeev8, B. McBreen1,

M. Mikkelsen12, M. Murray11, J. Natowitz8, B.S.Nielsen7, K. Olchanski1, D. Ouerdane7,

R.Planeta4, F. Rami2, D. Roehrich9, B. H. Samset12, D. Sandberg7, S. J. Sanders11,

R.A.Sheetz1, Z.Sosin3, P. Staszel7, T.S. Tveter12, F.Videbæk1, R. Wada8,

A.Wieloch3 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

Size of created medium?

y=0

y=1

y=2

y=3

Vast majority of data as well as models about elliptic flow concentrates on describing phenomena at midrapidity.

That is great, but how about longitudinal information?

Elliptic flow at Midrapidity

Phys. Rev. Lett. 86 (2001) 402

STAR

STAR

At midrapidity, several measurements of elliptic flow have been reported at RHIC.

Hydrodynamic models describe the data well up to ~ 2GeV/c

PHENIX

Phys. Rev. Lett. 89 (2002) 212301-1

Not at midrapidity

PRC 65 (2002) 011901

nucl-ex/0403050

Phys. Rev. Lett. 88 202301 (2002)

BRAHMS

BRAHMS

At forward and backward rapidities, understanding of v2 is not quite sufficient.

The model seems to follow the pseudorapidity distribution.

The data exhibits sharp triangular shape.

BRAHMS Detector System

Two rotatable spectrometers: MRS and FS

Small solid angles

Modification to the SMA detector

Silicon has two rings

Before

After

6 segments per 2π

42 segments per 2π

SMA is rotated 90 deg

normal to the beam axis.

Up to RUN03, BRAHMS had not been able to measure event planes.

Idea to measure event plane and flow

Measure event plane by global detectors: SMA and BBC

Look at the correlation between the angle between observed event angle and particle angle measured in the tracking detectors (MRS and FS).

Complication?

They are small solid angle spectrometers.

--- require large number of events.

--- may require corrections due to the missing

solid angles.

Equations

Reaction plane angle:

Currently, the preliminary data suggests the event plane resolutions of ~ 27 deg with n = 2.

Methods describe by

A. M. Poskanzer and S. A. Voloshin

Phys. Rev. C58 (1998) 1671

Conclusion

We can not show any results of elliptic flow at this time.

Can we measure v2 at η=0, 1, 2 and 3?

Do we have enough events? Yes (Hopefully)

Can we measure event plane? Yes.

Recently, it was pointed out that it is not necessary for flow measurement to know event planes.

Hironori Ito

2004-07-13T10:46:14