Elliptic Flow Analysis at BRAHMS

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Elliptic Flow Analysis at BRAHMS
Charged-particle anisotropy over pseudorapidity
and transverse momentum ranges of 0lt?lt3 and
0ltptlt3 in AuAu Collisions at vs_NN 200 GeV
Current status of BRAHMS elliptic flow analysis

• Hironori Ito
• BNL

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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 AM University, College Station. USA,
  9University of Bergen, Norway
• 10University of Bucharest, Romania, 11University
  of Kansas, Lawrence,USA
• 12 University of Oslo Norway

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Elliptic flow at Midrapidity
At midrapidity, several measurements of elliptic
flow have been reported at RHIC. Hydrodynamic
models describe the data well up to 2GeV/c
STAR
STAR
PHENIX
Phys. Rev. Lett. 86 (2001) 402
Phys. Rev. Lett. 89 (2002) 212301-1
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Not at midrapidity
BRAHMS
Phys. Rev. Lett. 88 202301 (2002)
PRC 65 (2002) 011901
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.
nucl-ex/0403050
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BRAHMS Detector System
Two rotatable spectrometers MRS and FS Small
solid angles
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Modification to the SMA detector
Up to RUN03, BRAHMS had not been able to measure
event planes.
Silicon has two rings
SMA is rotated 90 deg normal to the beam axis.
Before
After
6 segments per 2p
42 segments per 2p
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Equations
Methods describe by A. M. Poskanzer and S. A.
Voloshin Phys. Rev. C58 (1998) 1671
Reaction plane angle
Currently, the preliminary data suggests the
event plane resolutions of 27 deg with n 2.
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Conclusion
We can not show any results of elliptic flow at
this time. Can we measure v2 at ?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.