Anisotropic flow in AuAu and CuCu at 62 GeV and 200 GeV

1
Anisotropic flow in AuAu and CuCuat 62 GeV and
200 GeV
Gang Wang (Kent State, Ohio) for the STAR
Collaboration

• Introduction
• ? Flow Fourier coeffs (Oldenburg talk
  others)
• ? v1(y) structure
• ? ZDC upgrade
• ? Flow Study with ZDC-SMD
• Physics results
• ? v1 in 62 GeV AuAu, 10 - 70 centrality
• ? v1 in 62 GeV AuAu, centrality dependence
• ? v1 in 200 GeV AuAu, centrality dependence
• ? v2 in 200 GeV AuAu, 20 - 70 centrality
• ? v2 in 200 GeV CuCu, 20 - 60 centrality
• ? v2 in 200 GeV CuCu, centrality dependence
• Summary

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v1(y) structure
Models predict that anti-flow/3rd flow component,
with QGP ? v1(y) flat or a wiggle structure.
J. Brachmann et al. PRC 61, 024909 (2000)
L.P. Csernai, D. Rohrich PLB 458, 454 (1999)
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v1(y) structure
Models without QGP also predict a wiggle
structure in peripheral or mid-peripheral events.
M. Bleicher and H. Stöcker, PLB 526, 309 (2002)
RQMD
Baryon stopping and positive space-momentum
correlation
uRQMD
R. Snellings, H. Sorge, S. Voloshin, F. Wang, N.
Xu, PRL 84, 2803 (2000) also H. Liu et al., PRC
59, 348 (1999).
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v1 - experimental complications
Directed flow is small at RHIC, especially in the
central rapidity region, and analyses are easily
confused by non-flow effects (azimuthal
correlations not related to the reaction plane
orientation).
To reduce sensitivity to non-flow recent review
in PRC 72, 014904 (2005)
v13 -- the three-particle cumulant
method v1EP1, EP2 -- the event plane method
with mixed harmonics v1ZDC-SMD -- the
standard method with the 1st-order event plane
determined from the sideward deflection
(bounce-off) of spectator neutrons in the
Shower Max detector (SMD) of the Zero Degree
Calorimeters (ZDCs).
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STAR ZDC-SMD

• New knowledge of the direction of the impact
  parameter vector
• Minimal, if any, non-flow effects
• Minimal, if any, effects from flow fluctuations
• Worse resolution than from TPC, but that
  disadvantage is minor

SMD is 8 horizontal slats 7 vertical slats
located at 1/3 of the depth of the ZDC
ZDC side view
Scintillator slats of Shower Max Detector
Transverse plane of ZDC
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Flow study with ZDC-SMD 4 terms
In analysis
To systematically study the method with ZDC-SMD,
we can use the sub event plane from only east or
west ZDC-SMD, instead of the full event plane,
and even break down the correlation into X and Y
direction.
For example
Definitions of 4 terms
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Charged hadrons v1 in 62 GeV Au Au
Au Au 62 GeV
STAR preliminary
Models do well at larger h but their v1(h) is
too flat near h0
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Charged hadrons v1 in 62 GeV Au Au
STAR preliminary
directed flow of charged particles is opposite to
spectator bounce-off at all centralities, and
three methods agree.
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Charged hadrons v1 in 200 GeV Au Au
Au Au 200 GeV
STAR preliminary
Similar trends in AuAu v1(h) vs. centrality from
SPS thru top RHIC energy 200 GeV central
collisions allow v1 sign-change to be probed
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Charged hadrons v2 in 200 GeV Au Au
Systematic check on v2 measurements using ZDC-SMD
1st harmonic event plane shows substantial
non-flow effects in peripheral collisions.
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v2 minimizing non-flow for CuCu analysis
In this talk, we use this subset of elliptic flow
analysis methods to reduce sensitivity to
non-flow for CuCu recent review in PRC 72,
014904 (2005) v24 -- four-particle
cumulant v2AA-pp -- the scalar
product method v2qdist -- involves fit
to distribution of q flow vector Q /vM the
fit contains a term to account for non-flow.
particle azim from given pt bin
assume can be obtained from pp
Sum over multiplicity, M
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Charged hadrons v2 in 200 GeV CuCu
v2 for CuCu is smaller than for AuAu but large
relative size of CuCu non-flow divergence among
methods at higher pt requires further
investigation
13
Charged hadrons v2 in 200 GeV CuCu
Integrated v2(0.15 lt pt lt 2 GeV/c) again shows
lower flow for CuCu agreement on non-flow
correction
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Summary

• STAR ZDC-SMD allows the reaction plane to be
  determined with useful resolution from the
  bounce-off of spectator neutrons. This has
  been used to study charged particle v1 and v2 for
  62 and 200 GeV AuAu 200 GeV CuCu.
• Charged particles in the h-region covered by the
  STAR TPC and FTPCs (up to h 4.0)
  predominantly have opposite directed flow from
  the spectator nucleons. For 62 GeV AuAu, several
  models agree well in FTPC region, but their v1(h)
  is too flat at central pseudorapidities.
• 62 200 GeV AuAu show a complex structure in v1
  vs. h vs. centrality, and present a major
  challenge to models. 200 GeV central collisions
  allow v1 sign change near h 3.5 to 4 to be
  probed.

• For 200 GeV AuAu, v2ZDC-SMD allows
  nonflow-corrected elliptic flow to be extended to
  more peripheral centralities.
• The relative importance of non-flow is greater
  for CuCu analysis than for AuAu initial v2
  estimates for 200 GeV CuCu based on v24,
  v2CuCu-pp and v2qdist show reasonable
  consistency across broad regions of centrality
  and pT .

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• Backup Slides

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Limiting Fragmentation in Au Au
It has been observed that particle emission(both
spectra and flow) as a function of rapidity in
the vicinity of beam rapidity appears unchanged
over a wide range of beam energies, a pattern
known as limiting fragmentation.
STAR preliminary
The hypothesis holds here.
ycm 0