Transcript talk - particle.cz

Elliptic and Radial Flow in
High Energetic Nuclear Collisions
Marcus Bleicher (& Xianglei Zhu)
Institut für Theoretische Physik
Goethe Universität Frankfurt
Germany
Marcus Bleicher, ISMD 2005
Thanks to
• Elena Bratkovskaya
• Sascha Vogel
• Stephane Haussler
• Hannah Petersen
• Diana Schumacher
• Nu Xu
Marcus Bleicher, ISMD 2005
The tool: UrQMDv2.2
•
•
•
•
Non-equilibrium transport model
Hadrons and resonances
String excitation and fragmentation
Cross sections are parameterized
via AQM or calculated by detailed balance
• pQCD hard scattering at high energies
• Generates full space-time dynamics of hadrons
and strings
Marcus Bleicher, ISMD 2005
Transverse Momentum
Distributions: Proton-Proton
• PP works well
• pQCD needed at RHIC
• PYTHIA included in
UrQMD 2.x and HSD
Marcus Bleicher, ISMD 2005
Proton-Nucleus
• pA is well under control
• CC and SiSi are also under control
Inv. slope
• What about AA?
System size
Marcus Bleicher, ISMD 2005
Transverse
mass spectra
• Standard UrQMD and HSD
underestimate the data
• Additional resonances of 2-3 GeV
mass may improve the description
mt-m0
Marcus Bleicher, ISMD 2005
Inverse slope systematics
• ‘Step’ claimed to be signature of
QGP onset (Gazdzicki)
• High mass resonances improve
the description at low and high
energies
• How can we test those scenarios?
use v2 to disentangle early
and late stage
E_CM (AGeV)
Marcus Bleicher, ISMD 2005
Anisotropic flow
Fourier expansion of the transverse
angular distribution of the emitted particles:
dN
1
dN 


1  2v icos(i(  R ))

pt dp t dyd 2 p t dp t dy 
i1

Reaction Plane
pt  p2x  p2y
vn  cos(n(   R )) 
v1– directed flow
V2 -- elliptic flow
Marcus Bleicher, ISMD 2005

Elliptic flow
coordinate-space-anisotropy

momentum-space-anisotropy
y
x
 y2  x2
 2
 y  x2
py
v 2  cos2 ,   tan ( )
px
1
1) V2 of low pt particles is the good measure the EOS of
the fireball in the early stage.
2) V2 of high pt particles is the good measure of jet energy
loss through the medium.
Marcus Bleicher, ISMD 2005
Hints from elliptic flow
• High mass resonances
can not explain
scaled v2 above 40 AGeV
• Data shows saturation of scaled v2
• Strong hint for large pressure
and short mean free paths in the
early stage of the reaction
already from 30 AGeV on !
Data for hMarcus Bleicher, ISMD 2005
‘Partonic’ dof already at
low SPS energy
•Breakdown of v2/<pt> scaling
in model coincides with
onset of ‘partonic’ matter
 signals onset of change of
EoS in the early stage
Marcus Bleicher, ISMD 2005
V2 at RHIC
•
•
•
•
Magnitude of v2 is large
Meson-baryon ordering
Constituent quark scaling
Decrease of v2 at high pt
Are these unique QGP signatures?
Marcus Bleicher, ISMD 2005
Elliptic flow:
Centrality dependence
• Integral flow
STAR data is from
nucl-ex/0409033
V2 from UrQMD is about 50% smaller than the data,
Left space for parton rescattering?
Marcus Bleicher, ISMD 2005
Cumulant method results
• Integral flow
In the most central bin:
The fluctuations give
larger v2{6} but smaller
v2{4}
In the very peripheral
bins:
The fluctuations give
larger v2{6} and v2{4}
Agree with the prediction
of MCG model
BUT:
In the semi-central bins:
the v2 fluctuations can
be neglected.
Marcus Bleicher, ISMD 2005
Cumulant method results
• Comparison to STAR
data
Good agreement of
the ratios with
STAR data.
Decrease of g2 at
peripheral bins are
also reproduced.
(the g2 decrease is
possibly from the
v2 fluctuations)
Marcus Bleicher, ISMD 2005
Cumulant method results
• Differential flow
At large eta, the
non-flow effects are
less obvious. If the
v2 fluctuations are
also negligible to the
cumulant method,
the v2{2}, v2{4}
and v2{6} should all
agree with the exact
v2.
Marcus Bleicher, ISMD 2005
Cumulant method results
• Differential flow
v2{2} is heavily
affected by the
non-flow effects
especially at large
pt.
The non-flow
effects have been
eliminated in v2{4}
and v2{6}.
But v2{4} is still a
little larger than
the exact v2.
Marcus Bleicher, ISMD 2005
V2(pt) from UrQMD
Red--Mesons
Blue-Baryons
1)
2)
3)
4)
Clear separation of meson and baryon v2
Low pt, v2(meson)>v2(baryon)
High pt, v2(m)<v2(b)
The v2’s of multi-strange baryons are comparable to light baryons
Marcus Bleicher, ISMD 2005
NCQ-scaling
Note:
multi-strange
baryons follow
the normal
matter
NCQ-scaling of v2 is roughly reproduced in UrQMD!
Marcus Bleicher, ISMD 2005
Summary
At RHIC (transport models w/ strings and hadrons):
 Part of v2 might also come from hadronic stage
 Mass ordering is correct
 Constituent quark scaling (w/o ReCo!)
 non-flow correlations are correct
However, transport models w/o QGP produce to few pressure
in the early stage above 30 GeV
Marcus Bleicher, ISMD 2005