Anisotropic%20flow%20at%20RHIC%20from%20SPS%20to%20RHIC

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Anisotropic flow at RHIC from SPS to RHIC

• Raimond Snellings

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Introduction

• Heavy-Ion Collisions
• Study QCD at high temperature and density
• Establish and characterize properties of
  deconfined matter and the phase transition
• Requirement observables
• Provide information about the early, possibly
  deconfined phase
• Sensitive to the bulk properties

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Early stage high-pt probes

• Evidence of very dense system
• RAA, IAA
• Null experiment essential !

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Non-central heavy-ion collisions coordinate
system
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Calculating flow using multi particle correlations
Assumption all correlations between particles due
to flow Non flow correlation contribute order
(1/N), problem if vn1/vN
Non flow correlation contribute order (1/N3),
problem if vn1/N¾
N. Borghini, P.M. Dinh and J.-Y Ollitrault, Phys.
Rev. C63 (2001) 054906
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v2(pt) for high pt particles (self normalizing
tomography of dense matter)
M. Gyulassy, I. Vitev and X.N. Wang PRL 86 (2001)
2537
http//www.lbl.gov/nsd/annual/rbf/nsd1998/rnc/RNC.
htm R17. Event Anisotropy as a Probe of Jet
QuenchingR.S and X.-N. Wang R.S, A.M.
Poskanzer, S.A. Voloshin, STAR note,
arXivnucl-ex/9904003
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Charged particle v2 at high-pt
STAR preliminary
PHENIX preliminary
N. N. Ajitanand Nucl.Phys. A715 (2003) 765-768
K. Filimonov Nucl. Phys. A715 (2003) 737-740
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Elliptic flow at higher pt, extracted using
multi-particle correlations
Significant v2 up to 7 GeV/c in pt as expected
from jet quenching. However at intermediate pt
the magnitude is unexpectedly large
A. Tang (STAR) QM 2004
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More detailed information v2(pt) for identified
particles at higher-pt
PHENIX
STAR
Preliminary
ShinIchi Esumi Nucl. Phys. A715 (2003) 599
P. Sorensen
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Parton Coalescence/recombination?
D. Molnar, S.A. Voloshin Phys.Rev.Lett. 91
(2003) 092301
V. Greco, C.M. Ko and P. Levai nucl-th/0305024
C. Nonaka, R.J. Fries, S.A. Bass nucl-th/0308051
J. Castillo (STAR preliminary) QM2004
M. Kaneta (PHENIX) QM2004
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What about the bulk?

• Coordinate space configuration anisotropic
  (almond shape) however, initial momentum
  distribution isotropic (spherically symmetric)
• Only interactions among constituents generate a
  pressure gradient, which transforms the initial
  coordinate space anisotropy into a momentum space
  anisotropy (no analogy in pp)
• Multiple interactions lead to thermalization -gt
  limiting behavior ideal hydrodynamic flow

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Time evolution
SCIENCE Vol 298 2179 (2002)
Hydro calculation P. Kolb, J. Sollfrank and
U.Heinz

• Elliptic Flow reduces spatial anisotropy -gt self
  quenching

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Main contribution to elliptic flow develops early
in the collision
Zhang, Gyulassy, Ko, Phys. Lett. B455 (1999) 45
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Integrated Elliptic Flow
PHOBOS Phys. Rev. Lett. 89, 222301 (2002) 
PHENIX Phys. Rev. Lett. 89, 212301 (2002)
STAR Phys. Rev. Lett. 86, 402 (2001)
RQMD
First time in Heavy-Ion Collisions a system
created which at low pt is in quantitative
agreement with hydrodynamic model predictions for
v2 up to mid-central collisions
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Elliptic flow at lower energies
P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev.
C. C62 054909 (2000).
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Identified particle v2

• Typical pt dependence for different masses
• Heavy particles more sensitive to velocity
  distribution (less effected by thermal smearing)
  therefore put better constrained on EOS

STAR
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v2(pt,mass)

• All particles reasonably described at low-pt with
  common set of parameters
• PHENIX (squares) and STAR agree well

STAR, PHENIX preliminary
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Everything flows?
J. Castillo (STAR) QM2004
What about charm?
M. Kaneta (PHENIX) QM2004
pT GeV/c
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Conclusion

• Consistent measurements of elliptic flow from
  PHENIX, PHOBOS and STAR
• Elliptic flow for all measured particles at
  low-pt well described by boosted thermal particle
  distributions
• Flow is large indicative of strong partonic
  interactions at early stage of the collision
• In ideal hydro thermalization time lt 1 fm/c to
  describe the flow
• Up to pt 7 GeV/c sizable elliptic flow,
  consistent with parton energy loss
• Parton coalescence/recombination does a good job
  at intermediate pt important tests the precise
  v2 of the f-meson and the W

Hydro
ReCo
pQCD
R. Fries QM2004
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What have we learned from elliptic flow so far
(according to theorists)?

• U. Heinz Resulting in a well-developed
  quark-gluon plasma with almost ideal
  fluid-dynamical collective behavior and a
  lifetime of several fm/c (arXivhep-ph/0109006).
• E. Shuryak Probably the most direct signature of
  QGP plasma formation, observed at RHIC
  (arXivnucl-th/0112042).
• L. McLerran one needs very strong interactions
  amongst the quark and gluons at very early times
  in the collision (arXivhep-ph/0202025).
• M. Gyulassy The most powerful probe of the QGP
  equation of state the mass dependence of v2 One
  of the three lines of evidence for the QGP at
  RHIC (arXivnucl-th/0403032).

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Backup
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v2(pt) SPS-RHIC

• Integrated v2 depends on slope and ltptgt
• ltptgt pions 17 GeV 400 MeV/c, 130 GeV charged
  particles ltptgt 500 MeV/c

NA49 Phys. Rev. C68 (2003) 034903 CERES Phys.
Rev. Lett. 92 (2004) 032301
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Elliptic flow excitation function
NA49
Phys.Rev. C68 (2003) 034903
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Integrated v2 from cumulants
About 20 reduction from v22 to v24 v24
v26
A. Tang (STAR), AIP Conf. Proc. 698701, 2004
arXivnucl-ex/0308020
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Higher moments
ltv2ngt ? ltv2gtn
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The possible fluctuation contribution
standard v22 overestimates v2 by 10, higher
order cumulant underestimate v2 by 10 at
intermediate centralities
M. Miller and RS, arXivnucl-ex/0312008
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Compare fluctuations to data
M. Miller and RS, arXivnucl-ex/0312008
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Why is v2 so large at higher-pt?
Measured v2 values seem to be larger than the
maximum values in the case of extreme quenching
-gt surface emission
E. Shuryak nucl-th/0112042
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Hydro Jet Quenching?
T. Hirano and Y. Nara nucl-th/0307015
X.-N. Wang nucl-th/0305010
Coupling of hydro and parton energy loss gives a
reasonable description of the data and also has a
mass dependence at higher-pt
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How has elliptic flow defined our view of physics
at RHIC?

• Charged particle elliptic flow at low pt one of
  the first papers from RHIC
• First time quantitative agreement with
  hydrodynamics -gt suggestive of early
  thermalization, strongly interacting parton phase
• Identified particle elliptic flow at low pt
• QGP equation of state (phase transition) provides
  accurate description
• Charged particle elliptic flow at higher pt
• First indications of jet quenching (later RAA)
• Strongly dissipative system -gt limiting surface
  emission (later back to back suppression).
  Suggested by Shuryak for high-pt v2, earlier
  already by Huovinen for whole pt range -gt Not the
  whole answer at low pt shown by mass dependence
  of v2(pt) for p, K, p.
• Identified particle elliptic flow at higher pt
• Surface emission, not whole answer at higher pt
  either shown by mass dependence of v2 of pion,
  Kaon, proton and Lambda
• pion, Kaon, proton and Lambda v2 give indication
  for parton coalescence. First suggested at QM2002
  by Voloshin (later also used for RAA intermediate
  pt mass dependence)

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v2 at LHC energy
P. Kolb, J. Sollfrank, and U. Heinz, Phys. Rev.
C. C62 054909 (2000).
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Flow (radial, directed and elliptic)

• Only type of transverse flow in central collision
  (b0) is transverse flow.
• Integrates pressure history over complete
  expansion phase

• Elliptic flow, caused by anisotropic initial
  overlap region (b gt 0).
• More weight towards early stage of expansion.

• Directed flow, sensitive to earliest collision
  stage (pre-equilibrium, b gt 0)

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v1 predictions (QGP invoked)
L.P. Csernai, D. Rohrich Phys. Lett. B 458
(1999) 454
J. Brachmann et al., Phys. Rev. C. 61 024909
(2000)
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v1 predictions (more general, QGP interpretation
not necessary)
R.S., H. Sorge, S.A. Voloshin, F.Q. Wang, N. Xu
Phys. Rev. Lett 84 2803 (2000)
M. Bleicher, H. Stocker Phys. Lett. B 526 (2002)
309 (UrQMD)
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Directed flow at the SPS (NA49)
NA49 Phys.Rev. C68 (2003) 034903
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First measurement of v1 at RHIC

• Confirms v2 is in-plane at RHIC
• Suggestive of limiting fragmentation picture
• Consistent with theory predictions
• The data with current statistics shows no sign of
  a wiggle (also does not exclude the magnitude of
  the wiggle as predicted

A. Tang, M. Oldenburg, A. Poskanzer, J. Putschke,
RS, S. Voloshin
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Is there boost invariance?PHOBOS v2(h)
PHOBOS Phys. Rev. Lett. 89, 222301 (2002) 
average over all centrality (Npart 200)
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Event Characterization

• How do we distinguish peripheral collisions from
  central collisions?

• b