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Direct Photons in 200 GeV p+p, d+Au, Au+Au

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Presentation on theme: "Direct Photons in 200 GeV p+p, d+Au, Au+Au"— Presentation transcript:

1 Direct Photons in 200 GeV p+p, d+Au, Au+Au
Stefan Bathe UC Riverside for the PHENIX collaboration Changed title QM 2005, Budapest, August 4-9

2 Why Direct Photons? A+A p+p: d+Au
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 p+p: Test of QCD Reduce uncertainty on pQCD photons in A+A d+Au Study nuclear effects QM05 Stefan Bathe

3 Hard Photons p+p QM05 Stefan Bathe

4 New for QM: PHENIX Preliminary
Direct Photons in p+p PbSc good agreement with NLO pQCD Important baseline for Au+Au PbSc New for QM: PHENIX Preliminary Poster O. Zaudtke PbGl new Poster A. Hadj Henni QM05 Stefan Bathe

5 Hard Photons d+Au QM05 Stefan Bathe

6 Direct g 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
Recently published PRL 94, Expectation for Ncoll scaling of direct photons holds for all centrality classes p0 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 thermal: hard: QM05 Stefan Bathe

11 Going to low pT No significant excess at low pT QM05 Stefan Bathe

12 New from Run4 New data set Selection of most stable runs
Re-evaluation of systematic uncertainties Stay tuned for more improvements Poster T. Sakaguchi QM05 Stefan Bathe

13 Thermal Photons A New Approach
Au+Au A New Approach QM05 Stefan Bathe

14 Opening up the phase space
direct photon analysis pT new dilepton analysis conventional dilepton analysis Minv QM05 Stefan Bathe

15 The Idea g* g g p0 e+ g* e- q g e+ e- q Start from Dalitz decay
Compton q g* g e+ e- Compton q g The Idea p0 g e+ e- g* Start from Dalitz decay Calculate invariant mass distribution of Dalitz pairs invariant mass of Dalitz pair invariant mass of Dalitz pair invariant mass of virtual photon invariant mass of virtual photon form factor form factor phase space factor phase space factor Now direct photons Any source of real g produces virtual g with very low mass Rate and mass distribution given by same formula No phase space factor for mee<< pT photon What are Feynman graphs for virtual photons? QM05 Stefan Bathe

16 Method ÷ ÷ ÷ Material conversion pairs removed by analysis cut
Combinatorics removed by mixed events 0-30 90-140 MeV Rdata ÷ ÷ ÷ Calculate ratios of various Minv bins to lowest one: Rdata If no direct photons: ratios correspond to Dalitz decays If excess: direct photons QM05 Stefan Bathe

17 QM05 Stefan Bathe

18 g h p0 QM05 Stefan Bathe

19 S/B=~1 g h p0 h g p0 QM05 Stefan Bathe

20 ÷ Rh Rp0 Rdirect S/B=~1 g h p0 h g calculated from Dalitz formula p0
measured Rdata ÷ QM05 Stefan Bathe

21 ÷ Rh Rp0 Rdirect S/B=~1 g h p0 h g calculated from Dalitz formula p0
measured Rdata ÷ QM05 Stefan Bathe

22 ÷ ~25 % systematic error : ~20 % from measured h/p0 ratio
~10 % from g inclusive ~5 % acceptance Rh Rp0 Rdirect S/B=~1 g h p0 h g calculated from Dalitz formula measured with EMCal Here we are… p0 measured Rdata ÷ QM05 Stefan Bathe

23 Rdata MeV 0-20 % QM05 Stefan Bathe

24 g*direct/g*inclusive
0-20 % Significant 10% excess of very-low-mass virtual direct photons QM05 Stefan Bathe

25 Centrality Dependence
more peripheral Indication for centrality dependence QM05 Stefan Bathe

26 Comparison to Conventional result
( + 1 ) QM05 Stefan Bathe

27 gdirect QM05 Stefan Bathe

28 The Spectrum Compare to published Run2 result: PRL94 232301 QM05
Stefan Bathe

29 The Spectrum Compare to NLO pQCD L.E.Gordon and W. Vogelsang
excess above pQCD L.E.Gordon and W. Vogelsang Phys. Rev. D48, 3136 (1993) QM05 Stefan Bathe

30 The Spectrum t0=0.15 fm/c Compare to NLO pQCD
excess above pQCD L.E.Gordon and W. Vogelsang Phys. Rev. D48, 3136 (1993) Compare to thermal model D. d’Enterria, D. Perresounko nucl-th/ 2+1 hydro T0ave=360 MeV(T0max=570 MeV) t0=0.15 fm/c data above thermal at high pT QM05 Stefan Bathe

31 The Spectrum t0=0.15 fm/c Compare to NLO pQCD
excess above pQCD L.E.Gordon and W. Vogelsang Phys. Rev. D48, 3136 (1993) Compare to thermal model D. d’Enterria, D. Perresounko nucl-th/ 2+1 hydro T0ave=360 MeV(T0max=570 MeV) t0=0.15 fm/c data above thermal at high pT Compare to thermal + pQCD data consistent with thermal + pQCD 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 QM05 Stefan Bathe

34 Backup QM05 Stefan Bathe

35 QM05 Stefan Bathe

36 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 can be described under a variety of different assumptions, e.g.: Ti = MeV QGP + HG + pQCD (Non-boost inv. hydro) Huovinen, Ruuskanen, Räsänen (Nucl. Phys. A 650 (227) 1999) Ti = MeV Pure HG + pQCD (Non-boost inv. hydro) Ti = 335 MeV, t0 = 0,2 fm/c QGP + HG + pQCC (Bjorken hydro) Svrivastava (nucl-th/ ) 250 < Ti < 370 MeV, 0,5 < t0 < 3 fm/c QGP + HG + pQCD Renk (Phys.Rev.C67:064901,2003) Ti = MeV, t0 = 0,5 fm/c QGP + HG + pQCD without kT Ti = 205 MeV, t0 = 1 fm/c QGP + HG + pQCD with kT Turbide, Rapp, Gale (Phys.Rev.C69:014903,2004 ) Data consistent with QGP picture, but also with pure HG picture Large variations in extracted initial temperature Ti (however, most models give Ti > Tc) QM05 Stefan Bathe

38 New for QM: to be published
PHENIX p0 RdA--Final Cronin effect small! New for QM: to be published QM05 Stefan Bathe

39 QM05 Stefan Bathe

40 90-140 MeV, % QM05 Stefan Bathe

41 fragmentation contribution (%)
Only Ncoll scaling? What about fragmentation photons? fragmentation contribution substantial in p+p parton energy loss in QGP reduces fragmentation contribution in Au+Au compensated by induced photon bremsstrahlung in QGP fragmentation contribution (%) Effects cancel? QM05 Stefan Bathe

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