Directed Flow of Charged Hadrons in 62.4 GeV Au Au Collisions

1
Directed Flow of Charged Hadrons in 62.4 GeV
AuAu Collisions

• Markus D. Oldenburg
• (for the STAR collaboration)
• Lawrence Berkeley National Laboratory
• Division of Nuclear Physics Fall Meeting
• Chicago, 10/29/2004

2
Overview

• Introduction
• Model Predictions for Directed Flow
• Measurements Results
• Summary and Outlook

3
Anisotropic Flow

• spatial anisotropy
• ? momentum anisotropy

• peripheral collisions produce an asymmetric
  particle source in coordinate space

• Fourier transformation of azimuthal particle
  distribution in momentum space yields
  coefficients of different order

• v1 directed flow
• v2 elliptic flow

4
Directed flow (v1) and the QGP phase transition
Anti-flow/3rd flow component, with QGP ? v1(?)
flat at mid-rapidity.
J. Brachmann, S. Soff, A. Dumitru, H. Stöcker, J.
Maruhn, W. Greiner, Bravina, Rischke, PRC 61
(2000), 024909 L.P. Csernai, D. Röhrich, PLB 458
(1999), 454 M. Bleicher and H. Stöcker, PLB 526
(2002), 309.
5
Directed flow (v1) and baryon stopping
Positive space-momentum correlation, no QGP
necessary ? v1(?) wiggle.
R. Snellings, H. Sorge, S. Voloshin, F. Wang, N.
Xu, PRL 84 (2000), 2803.
6
Directed flow (v1) at RHIC at 200 GeV
charged particles

• shows no sign of a wiggle or opposite slope at
  midrapidity
• Predicted magnitude of a wiggle couldnt be
  excluded.

J. Adams et al. (STAR collaboration), PRL 92
(2004), 062301.
7
Charged particle v1(?) at 62.4 GeV
STAR preliminary

• Three different methods
• v13
• v1EP1,EP2
• v1ZDCSMD
• Sign of v1 is determined with spectator neutrons.
  
• No wiggle, opposite slope, or flatness at
  midrapidity observable!

charged particles
8
Centrality dependence of v1(?) at 62.4 GeV
most peripheral

• Different centrality bins show similar behavior.
• Methods agree very well.
• Most peripheral bin shows largest flow.

STAR preliminary
charged particles
most central
9
Comparison of different beam energies
STAR preliminary

• Data shifted with respect to beam rapidity.
• good agreement at forward rapidities
• In the fragmentation region the particle
  composition might be different!

charged particles
ydiff y200GeV y17.2,62.4GeV y200GeV
5.37 y62.4GeV 4.20 y17.2GeV
2.92

• NA49 data taken from
• C. Alt et al. (NA49 Collaboration), Phys. Rev.
  C 68 (2003), 034903.

10
Summary and Outlook

• Directed flow v1 of charged particles at 62.4 GeV
  was measured.
• No indication of a wiggle or opposite/zero
  slope at midrapidity at 62.4 GeV.
• At forward rapidities our signal agrees with
  measurements at 17.2 and 200 GeV.
• Measurements of identified particle v1 at
  midrapidity will further constrain model
  predictions.
• High statistics measurement of v1 at 200 GeV to
  come.