direct photons in 200 gev p+p , d +au, au+au
DESCRIPTION
Direct Photons in 200 GeV p+p , d +Au, Au+Au. Stefan Bathe UC Riverside for the PHENIX collaboration. QM 2005, Budapest, August 4-9. p+p : Test of QCD Reduce uncertainty on pQCD photons in A+A - PowerPoint PPT PresentationTRANSCRIPT
Direct Photons in 200 GeV p+p, d+Au, Au+Au
Stefan Bathe UC Riverside
for the PHENIX collaboration
QM 2005, Budapest, August 4-9
QM05 Stefan Bathe 2
Why Direct Photons?
● p+p:
♦ Test of QCD
• Reduce uncertainty on pQCD photons in A+A
● d+Au
♦ Study nuclear effects
● A+A
♦ Photons don’t strongly interact with produced medium
♦ Hard photons
• Allow test of Ncoll scaling for hard
processes• Important for interpretation of high-pT hadron suppression at
RHIC
♦ Thermal photons
• Carry information about early stage of collision
• QGP potentially detectable via thermal photon radiation
QM05 Stefan Bathe 3
Hard Photons
p+p
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Direct Photons in p+p● good agreement with NLO
pQCD
● Important baseline for Au+Au
PbSc
at 200 GeVp p s+ =
PbSc
New for QM: PHENIX Preliminary
Poster O. Zaudtke
PbGlnew
Poster A. Hadj Henni
QM05 Stefan Bathe 5
Hard Photons
d+Au
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Direct in d+Au
● p+p and d+Au spectra compared to NLO pQCD
● ratio to NLO pQCD
● consistent with 1
● No indication for nuclear effects
2
Poster H. Torii
Poster D. Peressounko
QM05 Stefan Bathe 7
Hard Photons
Au+Au
QM05 Stefan Bathe 8
Direct Photons in Au+Au
PRL 94, 232301
Expectation for Ncoll scaling of
direct photons
Recently published
holds for all centrality classes
0 suppression caused by medium created in Au+Au collisions
QM05 Stefan Bathe 9
Thermal Photons
Au+Au
QM05 Stefan Bathe 10
Schematic Photon Spectrum in Au+Au
Decay photons
nT
1
phard:
/ E Tethermal:
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Going to low pT
● No significant excess at low pT
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● New data set
● Selection of most stable runs
● Re-evaluation of systematic uncertainties
New from Run4
● Stay tuned for more improvements Poster T. Sakaguchi
QM05 Stefan Bathe 13
Thermal Photons
Au+Au
A New Approach
QM05 Stefan Bathe 14
Opening up the phase space
Minv
pT
direct photon analysis
new dilepton analysis
conventional dilepton analysis
0
QM05 Stefan Bathe 15
phase space factorform factorinvariant mass of virtual photon
invariant mass of Dalitz pair
phase space factorform factorinvariant mass of Dalitz pair
invariant mass of virtual photon
32
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2
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)2
1(4
13
21
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The Idea
32
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22 )( eemF
● Start from Dalitz decay
● Calculate invariant mass distribution of Dalitz pairs
● Now direct photons
● Any source of real produces
virtual with very low mass
● Rate and mass distribution given by same formula
♦ No phase space factor for mee<< pT
photon
0
0
e+
e-
Compton
q
g q
Compton
q
g q
e+
e-
QM05 Stefan Bathe 16
● Calculate ratios of various Minv bins to lowest one: Rdata
● If no direct photons: ratios correspond to Dalitz decays
● If excess: direct photons
Method
÷
÷÷
0-3
0
90-1
40
140-2
00 M
eV
200-3
00
Rdata
● Material conversion pairs removed by analysis cut
● Combinatorics removed by mixed events
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QM05 Stefan Bathe 19
S/B=~1
QM05 Stefan Bathe 20
S/B=~1
R
R
Rdirect
0
0
direct
data
incl.
direct
*
*
RR
RR
calculated from Dalitz formula
measuredRdata ÷
QM05 Stefan Bathe 21
S/B=~1
0
0
direct
data
incl.
direct
*
*
RR
RR
calculated from Dalitz formula
measuredRdata ÷
R
R
Rdirect
QM05 Stefan Bathe 22
S/B=~1
0
0
direct
data
incl.
direct
*
*
RR
RR
calculated from Dalitz formula
measuredRdata ÷
R
R
Rdirect
incl.
direct
measured with EMCal
Here we are…
~25 % systematic error :
~20 % from measured 0 ratio
~10 % from inclusive
~5 % acceptance
QM05 Stefan Bathe 23
140-200 MeV0-20 %
Rdata
0
0
direct
data
incl.
direct
*
*
RR
RR
incl.
direct
QM05 Stefan Bathe 24
*direct/*inclusive
Significant 10% excess of very-low-mass virtual direct photons
0
0
direct
data
incl.
direct
*
*
RR
RR
incl.
direct
0-20 %
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Centrality Dependence
Indication for centrality dependence
more peripheral
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Comparison to Conventional result
0
0
direct
data
incl.
direct
*
*
RR
RR
incl.
direct
( + 1 )
QM05 Stefan Bathe 27
direct
0
0
direct
data
incl.
direct
*
*
RR
RR
incl.
direct
QM05 Stefan Bathe 28
The Spectrum
Compare to published Run2 result: PRL94 232301
0
0
direct
data
incl.
direct
*
*
RR
RR
incl.
direct
QM05 Stefan Bathe 29
The SpectrumCompare to NLO pQCD
• excess above pQCD
• L.E.Gordon and W. Vogelsang
• Phys. Rev. D48, 3136 (1993)
QM05 Stefan Bathe 30
The Spectrum
Compare to thermal model
• data above thermal at high pT
2+1 hydro
T0ave=360 MeV(T0
max=570 MeV)
0=0.15 fm/c
• D. d’Enterria, D. Perresounko
• nucl-th/0503054
Compare to NLO pQCD
• excess above pQCD
• L.E.Gordon and W. Vogelsang
• Phys. Rev. D48, 3136 (1993)
QM05 Stefan Bathe 31
The Spectrum
Compare to thermal + pQCD• data consistent with
thermal + pQCD
Compare to thermal model
• data above thermal at high pT
• D. d’Enterria, D. Perresounko
• nucl-th/0503054
Compare to NLO pQCD
• excess above pQCD
• L.E.Gordon and W. Vogelsang
• Phys. Rev. D48, 3136 (1993)
2+1 hydro
T0ave=360 MeV(T0
max=570 MeV)
0=0.15 fm/c
QM05 Stefan Bathe 32
Conclusions
● Hard direct photons pT>4GeV/c
♦ p+p:
• Spectrum consistent with pQCD calculations
♦ d+Au:
• No apparent nuclear effects
♦ Au+Au:
• Confirms Ncoll scaling for hard processes
● Thermal (?) direct photons 1<pT<4GeV/c
♦ New EMCal measurement with reduced systematics
• Stay tuned for further improvements
♦ New measurement through very-low-mass virtual photons
• Significant 10% direct photon excess above decay photons
• Spectrum consistent with thermal model
QM05 Stefan Bathe 33
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Backup
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WA98 Interpretation: T or kT ?
● QGP + HG rates convoluted with simple fireball model plus pQCD hard photons
● Data described with initial temperature Ti=205 MeV + some nuclear kT broadening (Cronin-effect)
● Data also described without kT broadening but with high initial temperature (Ti=270 MeV)
Turbide, Rapp, Gale, Phys. Rev. C 69 (014902), 2004
QM05 Stefan Bathe 37
WA98 Data: Conclusions
● Data consistent with QGP picture, but also with pure HG picture
● Large variations in extracted initial temperature Ti (however, most models give Ti > Tc)
Data can be described under a variety of different assumptions, e.g.:
Ti = 214 - 255 MeVQGP + HG + pQCD(Non-boost inv. hydro) Huovinen, Ruuskanen, Räsänen
(Nucl. Phys. A 650 (227) 1999)Ti = 213 - 234 MeVPure HG + pQCD
(Non-boost inv. hydro)
Ti = 335 MeV, = 0,2 fm/c
QGP + HG + pQCC(Bjorken hydro)
Svrivastava (nucl-th/0411041)
250 < Ti < 370 MeV,0,5 < < 3 fm/c
QGP + HG + pQCDRenk (Phys.Rev.C67:064901,2003)
Ti = 250 - 270 MeV, = 0,5 fm/c
QGP + HG + pQCD without kT
Ti = 205 MeV, = 1 fm/c
QGP + HG + pQCD with kTTurbide, Rapp, Gale
(Phys.Rev.C69:014903,2004 )
QM05 Stefan Bathe 38
PHENIX 0 RdA--Final
Cronin effect small!
New for QM: to be published
QM05 Stefan Bathe 39
QM05 Stefan Bathe 40
90-140
90-140 MeV, 20-40 %
QM05 Stefan Bathe 41
Only Ncoll scaling?
● What about fragmentation photons?
frag
men
tati
on
con
trib
uti
on
(%
)
● fragmentation contribution substantial in p+p
● parton energy loss in QGP reduces fragmentation contribution in Au+Au
● compensated by induced photon bremsstrahlung in QGP
● Effects cancel?