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Neutral Pions in 200 GeV Cu+Cu Collisions. Stefan Bathe UC Riverside for the PHENIX Collaboration. DNP/JPS 2005, Maui, September 20. no effect. Hard Scattering and R AA. Hard processes yield scales with N coll small cross section incoherent superposition - PowerPoint PPT Presentation
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DNP/JPS ’05 Stefan Bathe 1
Neutral Pions in 200 GeV Cu+Cu Collisions
Stefan Bathe UC Riverside
for the PHENIX Collaboration
DNP/JPS 2005, Maui, September 20
DNP/JPS ’05 Stefan Bathe 2
Hard Scattering and RAA• Hard processes
– yield scales with Ncoll
• small cross section
• incoherent superposition
• Nuclear Modification Factor RAA
• absence of nuclear effects: RAA=1 at high pT
• Strong suppression in central Au+Au
no effect
strongsuppression
TNNfAA
TAAAA
d/d
d/d0
0
pT
pNR
Phys.Rev.Lett.91:072301,2003
DNP/JPS ’05 Stefan Bathe 3
Cause for Suppression
• Initial- or final-state effect?– Non-suppression in d+Au
– Non-suppression of direct photons in Au+Au
• final-state effect
Phys.Rev.Lett.91:072303
Phys.Rev.Lett.94:232301,2005
• To learn more– study system-size
dependence
DNP/JPS ’05 Stefan Bathe 4
System-Size Dependence• Vary centrality
• Vary nucleus size– different geometrical
shape– more precise centrality
determination for small systems
Au+Au Cu+Cu
DNP/JPS ’05 Stefan Bathe 5
Npart(x,y)
ellipticity different
Au+AuA=197
60-94% 40-50% 20-30% 0-10%
<Npart>
Cu+CuA=64
6.3 19.5 45.5 114
80-92.2% 60-80% 50-60% 30-40%
6.4 25.4 53.0 98.2
centrality
centrality
Transverse Npart density for similar <Npart> in Au+Au and Cu+Cu
DNP/JPS ’05 Stefan Bathe 6
PHENIX Experimental Setup
• Central spectrometer arms || < 0.35– and 0, via 2-
decay– Electromagnetic
calorimeter (EMCal)• Lead scintillator
calorimeter (PbSc)• Lead glass calorimeter
(PbGl)
DNP/JPS ’05 Stefan Bathe 7
0 Spectra in 200 GeV Cu+Cu
• 56 M minimum-bias events
• 1.9 M high-pT events recorded, 2.2 B sampled
• pT range 1-17 GeV/c
• Also measured 62.4 GeV and 22.5 GeV– need p+p reference
DNP/JPS ’05 Stefan Bathe 8
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions
DNP/JPS ’05 Stefan Bathe 9
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions
DNP/JPS ’05 Stefan Bathe 10
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions
DNP/JPS ’05 Stefan Bathe 11
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions
DNP/JPS ’05 Stefan Bathe 12
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions
DNP/JPS ’05 Stefan Bathe 13
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions
DNP/JPS ’05 Stefan Bathe 14
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions
DNP/JPS ’05 Stefan Bathe 15
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions
DNP/JPS ’05 Stefan Bathe 16
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions• RAA ~ 0.4 for central collisions
DNP/JPS ’05 Stefan Bathe 17
0 RAA in 200 GeV Cu+Cu
• RAA ~ 1 in peripheral collisions• RAA ~ 0.4 for central collisions• Charged-hadron RAA larger in central collisions
Charged hadrons:see Carla Vale’s talk, BF11
DNP/JPS ’05 Stefan Bathe 18
Comparing Au+Au and Cu+Cu
Similar behavior for Au+Au and Cu+Cu for
same Npart
Suppression 2x stronger in central
Au+Au, but:
0
0
0
DNP/JPS ’05 Stefan Bathe 19
Model Comparison• Models
– parton energy loss through gluon radiation
– density and path-length dependend
• Models describe data well
Dainese, C. Loizides, G. Paic,Eur.Phys.J.C38:461,2005
I. Vitev,Phys.Rev.Lett.89:252301,2002
X. N. Wang,Phys.Lett.B595:165,2004
DNP/JPS ’05 Stefan Bathe 20
V. Pantuev,hep-ph/0506095,corona jet production
density and path-length dependend
Model Comparison
DNP/JPS ’05 Stefan Bathe 21
Corona Jet Production
V. Pantuev,hep-ph/0506095
• Different surface-to-volume ratio, different absorption for same Npart
DNP/JPS ’05 Stefan Bathe 22
Summary and Outlook• High-pT 0 (h+-) suppression in central Cu+Cu
at 200 GeV
• Suppression similar to that in Au+Au for same Npart
• Consistent with pure density and path-length dependence
• Hints for shape-dependent suppression mechanism for same system size
• More information from reaction-plane dependence
DNP/JPS ’05 Stefan Bathe 23
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