7 Relativistic Nucleus-Nucleus Collisions and the QCD Matter Phase Diagram
381
Fig. 7.41 The nuclear
modification factor R AA for
π 0 in min. bias Cu+Cu and
Au+Au collisions at
√
s = 200 GeV, in the range
p T > 7 GeV/c [175], plotted
vs. centrality as measured by
participant nucleon number
N part
N part
2.0
1.5
1.0
0.5
0 0
100
200
300
p
R T
B A
]
c
/
V
e
G 0
.
7
>
[
Integrated
200 GeV
R AuAu
Integrated
200 GeV
R CuCu
PHENIX preliminary
Fig. 7.42 R AA for π 0
production in central Au+Au
collisions at
√
s = 200 GeV
[175], compared to a
hydrodynamic calculation for
different opacities (transport
coefficients [195]) of the
plasma [204]
0
5
10
15
20
p T [GeV]
0
0.2
0.4
0.6
0.8
1.0
R A
A
PHENIX data
hydro evolution, opacity 1.5
×
hydro evolution
hydro evolution, opacity 2
×
p T > 7.0 GeV/c and is shown as a function of centrality, reflected by N part . We infer
a drastic suppression, by an R AA approx0.25 in near central collisions. Figure 7.42
shows the p T dependence [175] of neutral pion R AA in central Au+Au collisions
(N part = 350), with a suppression to below 0.2 at p T ≥ 4 GeV/c.
Note that R AA cannot reach arbitrarily small values because of the unattenuated contribution of quasi-in-vacuum surface “corona” single nucleon-nucleon
collisions, closely resembling the p + p → π 0 + X inclusive yield employed in
381
Fig. 7.41 The nuclear
modification factor R AA for
π 0 in min. bias Cu+Cu and
Au+Au collisions at
√
s = 200 GeV, in the range
p T > 7 GeV/c [175], plotted
vs. centrality as measured by
participant nucleon number
N part
N part
2.0
1.5
1.0
0.5
0 0
100
200
300
p
R T
B A
]
c
/
V
e
G 0
.
7
>
[
Integrated
200 GeV
R AuAu
Integrated
200 GeV
R CuCu
PHENIX preliminary
Fig. 7.42 R AA for π 0
production in central Au+Au
collisions at
√
s = 200 GeV
[175], compared to a
hydrodynamic calculation for
different opacities (transport
coefficients [195]) of the
plasma [204]
0
5
10
15
20
p T [GeV]
0
0.2
0.4
0.6
0.8
1.0
R A
A
PHENIX data
hydro evolution, opacity 1.5
×
hydro evolution
hydro evolution, opacity 2
×
p T > 7.0 GeV/c and is shown as a function of centrality, reflected by N part . We infer
a drastic suppression, by an R AA approx0.25 in near central collisions. Figure 7.42
shows the p T dependence [175] of neutral pion R AA in central Au+Au collisions
(N part = 350), with a suppression to below 0.2 at p T ≥ 4 GeV/c.
Note that R AA cannot reach arbitrarily small values because of the unattenuated contribution of quasi-in-vacuum surface “corona” single nucleon-nucleon
collisions, closely resembling the p + p → π 0 + X inclusive yield employed in