System Size and energy dependence of photon production measured with the PHENIX experiment at RHIC

1. photons Good thing about photons! dileptons No strong interaction once produced! Best probe bringing thermodynamical Information out of the system (Initial temperature, degree of freedom, time profile, etc.) Leading order (LO) fB: Bose dist. em: photon self energy • Compton scattering of quarks and gluons: q(q)gq(q) • Annihilation of quarks: qqg • NLO: Bremsstrahlung, NNLO: Fragment… Next to Leading order (NLO) What we learn from system and energy dependence of photon production? • Photon: hard + soft + hard-soft interplay • Results from different systems disentangle photon sources • Results from different energies give different signal to background ratios Low to Mid-pT region data (/0 double ratio) pQCD is LO! NLO pQCD: L.E.Gordon and W. Vogelsang, PRD48(1993)3136 Possible contribution in heavy ion collisions (Au+Au, CuCu) • Jet-Photon conversion due to secondary scattering of hard-scattered parton (4<pT<7GeV/c) • A prediction says almost same amount as pQCD contribution is expected • Thermal photon production in QGP(1<pT<3GeV) • ~10% of ’s from hadron decays • Hadron-gas interaction (pT<1GeV/c) • ()  (), K*  K Different Ncoll and Npart dependence! PHENIX Data! : d+A 200GeV PRC 72(2005)014906 • Expect kT broadening as is seen in E706 • Probably, some hint is here • Still in work to reduce systematic error nucl-th/0507018 A compilation on photons, PRC 69(2004)014903 PHENIX Detector View From Beam A complex apparatus to measure:Hadrons, Muons, Electrons, Photons View From Side Central Arms Coverage (E&W) -0.35< y < 0.35 30o <|f |< 120o Muon Arms Coverage (N&S) 1.2< |y| <2.3 -180o < f < 180o For the Quark Matter 2006 Conference at Shanghai, China, Nov 13-20, 2006 Takao Sakaguchi, Brookhaven National Laboratory, for the PHENIX Collaboration Au+Au sNN=200GeV • Brand New high pT direct photon spectra up to 18GeV/c • NLO pQCD calculation works relatively well. • Intermediate pT region show is of interest (5-10GeV/c) • For pT<3GeV/c, thermal photon contribution looks dominant • Jet-Photon conversion can describe the data for pT>3GeV/c • Uncertainty of p+p and d+Au result can overcome these contributions • Upcoming data disentangles the fraction of soft and hard component • AuAu 62GeV • CuCu 200, 64GeV RAA’s Latest direct photon spectra System Size and energy dependence of photon production measured with the PHENIX experiment at RHIC Initial hard scattering: p+p 200GeV • Calculable by NLO pQCD (pT>5GeV/c) • Comparison with p+p 200GeV collisions data • Calculation agrees data within error /0 double ratio The baseline in this collision energy Nuclear Effect • Prompt  and 0 production in -Be, p-Be, -Cu, p-Cu (Tevatron E706) • Cronin effect both in  and 0! • : kT broadening, p0: kT broadening + recombination p+p Data to fit function used for making RAA • Center-of-mass energy, and xT region: • RHIC: sNN=200GeV, xT ~0.04-0.25 • E706: sNN=32-40GeV, xT~0.2-0.5 PRD72, 032003(2005) • A dedicated experiments for direct photon search in relativistic heavy Ion collisions. • (PRL 85 (2000) 3595)sNN=17.3GeV • Data can be either explained by kT-smearing or higher initial temperature • Any data did not see pT>4GeV, where pQCD photons dominate • No information on kT does not allow us to resolve the issue. • Recent data points at ~100MeV available from WA98. • By analysis of correlation strength in interferometry, • PRL93(2004)022301 CERN (WA98) results WA98 data and theoretical interpretation PRC69(2004)014903 Estimate of background photons from sources listed above is also essential Good thing about CERN: less Jet production cross-section-> less pi0 background