Transcript Document

Anisotropic flow at RHIC
from SPS to RHIC
Raimond Snellings
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
v2  cos 2(   r ) ,
  tan (
1
py
px
)
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Calculating flow using multi
particle correlations
vn  cos n(   r )  ein (  ψr )
ein (1 2 )  ein (1  r ) ein ( r 2 )  ein (1  r )
ein ( r 2 )  (vn {2}) 2
Assumption all correlations between particles due to flow
Non flow correlation contribute order (1/N), problem if vn≈1/√N
ein (1 2 3 4 )  ein (1 2 ) ein (3 4 )  ein (1 4 ) ein (3 2 )  (vn {4}) 4
Non flow correlation contribute order (1/N3), problem if vn≈1/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)
v2  cos 2(  r )
r
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 Quenching
R.S and X.-N. Wang
R.S, A.M. Poskanzer, S.A. Voloshin, STAR note, arXiv:nucl-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
v2{2}
v2{RP}
v2{4}
Significant v2 up to ~7
GeV/c in pt as
expected from jet
quenching. However
at intermediate pt the
magnitude is
unexpectedly large
STAR Preliminary
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: nuclth/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
•
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 -> limiting
behavior ideal hydrodynamic flow
y
x
Momentum space

d 3N
1 d 2N 

E 3 
1

2
v
cos
n







 n
r

d p 2 pt dpt dy  n1

v2  cos 2(   r ) ,   tan (
1
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py
px
)
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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 -> 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)
STAR: Phys. Rev. Lett. 86, 402 (2001)
PHENIX: Phys. Rev. Lett. 89, 212301
(2002)
Hydrodynamic limit
STAR
PHOBOS
v2  cos 2(  r )
RQMD
Compilation and Figure from M. Kaneta
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
Hydro: P. Huovinen, P. Kolb, U. Heinz
STAR
Fluid cells expand with collective velocity v,
different mass particles get different Dp
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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 < 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 -meson and
the W
0
1
2
3
4
Hydro
5
6
7
8
9
10
11
12 GeV/c
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 (arXiv:hep-ph/0109006).
– E. Shuryak: Probably the most direct signature of QGP
plasma formation, observed at RHIC (arXiv:nuclth/0112042).
– L. McLerran: one needs very strong interactions amongst the
quark and gluons at very early times in the collision
(arXiv:hep-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 (arXiv:nucl-th/0403032).
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Backup
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v2(pt) SPS-RHIC
• Integrated v2
depends on
slope and <pt>
• <pt> pions 17
GeV ≈ 400
MeV/c, 130
GeV charged
particles <pt>
≈ 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
STAR
Phys.Rev. C68
(2003) 034903
NA49
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Integrated v2 from cumulants
About 20%
reduction from
v2{2} to v2{4}
v2{4} ≈ v2{6}
A. Tang (STAR), AIP Conf. Proc. 698:701, 2004;
arXiv:nucl-ex/0308020 Raimond Snellings; Moriond 2004
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Higher moments

y 2  x2
y 2  x2
v 
v2 {2} 
v22

2 2
2
v2 {4}  2 v
v2 {6} 
 v
1
4
6
2

1/ 4
 v
4
2
9 v
4
2
2
2
v
2 3
2
 12 v

1/ 6
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<v2n> ≠ <v2>n
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The possible fluctuation contribution
“standard”
v2{2}
overestimates
v2 by 10%,
higher order
cumulant
underestimate
v2 by 10% at
intermediate
centralities
M. Miller and RS,
arXiv:nucl-ex/0312008
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Compare fluctuations to data
M. Miller and RS,
arXiv:nucl-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 -> 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 -> 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 -> limiting surface emission (later back to back suppression).
Suggested by Shuryak for high-pt v2, earlier already by Huovinen for whole pt range -> Not the
whole answer at low pt shown by mass dependence of v2(pt) for , 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
S. Radomski
P. Kolb, J. Sollfrank,
and U. Heinz, Phys.
Rev. C. C62 054909
(2000).
(PPR) ALICE simulations
and reconstruction, show
that we will be in a beautiful
position to do this physics at
LHC
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Flow (radial, directed and elliptic)
y
x
y
x
x
z
• Only type of transverse flow in central collision
(b=0) is transverse flow.
• Integrates pressure history over complete
expansion phase
• Elliptic flow, caused by anisotropic initial
overlap region (b > 0).
• More weight towards early stage of expansion.
• Directed flow, sensitive to earliest collision stage
(pre-equilibrium, b > 0)
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v1 predictions (QGP invoked)
J. Brachmann et al., Phys. Rev. C. 61 024909 (2000)
L.P. Csernai, D. Rohrich:
Phys. Lett. B 458 (1999)
454
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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)
Preliminary v2200
average over
Final v2130
all centrality
(Npart ~200)
200
130
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Event Characterization
• How do we distinguish peripheral collisions from central
collisions?
•b
Ncoll
STAR
Npart
5% Central
Impact Parameter (b)
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