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

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

Hard Photons p+p QM05 Stefan Bathe

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

Hard Photons d+Au QM05 Stefan Bathe

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

Hard Photons Au+Au QM05 Stefan Bathe

Direct Photons in Au+Au Recently published PRL 94, 232301 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

Thermal Photons Au+Au QM05 Stefan Bathe

Schematic Photon Spectrum in Au+Au Decay photons thermal: hard: QM05 Stefan Bathe

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

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

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

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

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

Method ÷ ÷ ÷ Material conversion pairs removed by analysis cut Combinatorics removed by mixed events 0-30 90-140 200-300 140-200 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

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g h p0 QM05 Stefan Bathe

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

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

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

÷ ~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

Rdata 140-200 MeV 0-20 % QM05 Stefan Bathe

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

Centrality Dependence more peripheral Indication for centrality dependence QM05 Stefan Bathe

Comparison to Conventional result ( + 1 ) QM05 Stefan Bathe

gdirect QM05 Stefan Bathe

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

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

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/0503054 2+1 hydro T0ave=360 MeV(T0max=570 MeV) t0=0.15 fm/c data above thermal at high pT QM05 Stefan Bathe

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/0503054 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

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

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Backup QM05 Stefan Bathe

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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

WA98 Data: Conclusions Data can be described under a variety of different assumptions, e.g.: Ti = 214 - 255 MeV QGP + HG + pQCD (Non-boost inv. hydro) Huovinen, Ruuskanen, Räsänen (Nucl. Phys. A 650 (227) 1999) Ti = 213 - 234 MeV Pure HG + pQCD (Non-boost inv. hydro) Ti = 335 MeV, t0 = 0,2 fm/c QGP + HG + pQCC (Bjorken hydro) Svrivastava (nucl-th/0411041) 250 < Ti < 370 MeV, 0,5 < t0 < 3 fm/c QGP + HG + pQCD Renk (Phys.Rev.C67:064901,2003) Ti = 250 - 270 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

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

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90-140 90-140 MeV, 20-40 % QM05 Stefan Bathe

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