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Measurement of Electro-magnetic radiation at PHENIX

Measurement of Electro-magnetic radiation at PHENIX. Takao Sakaguchi Brookhaven National Laboratory for the PHENIX Collaboration. Electromagnetic radiation in URHIC. What is this? Quotes from the literature. Direct radiation from the matter produced, and no strong interaction after produced

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Measurement of Electro-magnetic radiation at PHENIX

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  1. Measurement of Electro-magnetic radiation at PHENIX Takao Sakaguchi Brookhaven National Laboratory for the PHENIX Collaboration

  2. Electromagnetic radiation in URHIC • What is this? • Quotes from the literature. • Direct radiation from the matter produced, and no strong interaction after produced • J/, , ,  are NOT electromagnetic probe in this sense. Of course, they are closely related to dilepton or photon production. They decay into electrons that don’t strongly interact matter. • Direct (thermal) photons, dileptons, direct electrons(?) • Production Process • Compton and annihilation (LO) • Fragmentation (NLO) • Photons come from all the stages. • Transparent in the strongly interacting medium • Carry thermodynamical information of the state • Temperature, Degree of freedom Measurement of direct photon production allows more definitive discrimination between initial- and final-state suppression due to the fact that photons, once produced, are essentially unaffected by the surrounding matter. Hence photons produced directly in initial parton scatterings are not quenched unless the initial parton distributions are suppressed in the nucleus.. (PHENIX, 2005) Photons and dileptons are potentially more direct probes of the early collision stages since they escape from the impact zone nearly undisturbed by final-state interactions and have their largest emission rates in hot and dense matter. Moreover, according to the vector dominance model, dilepton production is mediated in the hadronic phase by the light neutral vector mesons ρ, ω, and φ which mark the low-mass region by distinctive resonance peaks. (CERES, 2005) …Since the mean free path of the produced photons is considerably larger than the size of the nuclear volume, photons produced throughout all stages of the collision will be observable in the final state. …., thereby provide evidence for the possible formation of a quark gluon plasma (QGP). (WA70, 1996) direct fragment Takao Sakaguchi, BNL

  3. photons dileptons fB: Bose dist. em: photon self energy Sources of Radiation • Thermal radiation from QGP (1<pT<3GeV) • 5-10% of ’s from all the hadron decays • Compton, annihilation of quarks • Annihilation also can be seen in dilepton spectra • Hadron-gas interaction (pT<1GeV/c): ()  (), K*  K A compilation on photons, PRC 69(2004)014903 Takao Sakaguchi, BNL

  4. Hard scattered partons interact with thermal partons in matter Sources of Radiation (jet driven) • Compton scattering of hard scattered and thermal partons (Jet-photon conversion) • A prediction: J-P  pQCD in 2<pT<3GeV/c, and ~50% @ 5GeV • Another prediction: J-P  pQCD even at 5GeV • Bremsstrahlung from hard scattered partons in medium A comparison of Run2 data and Jet-photon conversion calculation R. Fries et al., PRC72, 041902(2005) C. Gale, NPA774(2006)335 Takao Sakaguchi, BNL

  5. Same sources seen in dileptons • Comparison of “High pT low mass” and “High mass, low pT” dilepton will disentangle interplay of various contributions High pT, low mass High mass, low pT S. Turbide, QM2006 Takao Sakaguchi, BNL

  6. Dileptons in Au+Au collisions Low “energy” photons • 200GeV Au+Au Minimum bias • 870M events • pTe>0.3GeV/c • Compared with various contributions • Fit the pion spectra • Other mesons estimated from p0 • Ex. h/p0 = 0.45 ±0.10 • J/y yield is adjusted to reflect real suppression • Filtered into the Ideal PHENIX acceptance • Charm contribution generated using PYTHIA • Scaled by Ncoll • Doesn’t consider charm suppression • No additional scaling between cocktail and data • ie. Not scaled by 1/Np0 Takao Sakaguchi, BNL

  7. Possible IMR(1100-2900) Sources Correlated Charm pairs Thermal Sources Similar to high pT(pT>3GeV/c) single electron suppression pattern Attributed to charm suppression Different from low pT (pT>0.3GeV/c) single electrons Thermal sources probably underlying in this region, but not identified. Shape Comparison Only PHENIX Preliminary PHENIX preliminary PHENIX preliminary Dileptons in IMR(1-3GeV/c2) Y(1100-2900)/Y(0-100) RCP for IMR RCP for IMR, RAA for single particles Takao Sakaguchi, BNL

  8. How about low mass region? Very low “energy” photons. • Ratio of Yield in 150-300MeV/c2 to 0-100MeV/c2 region. • Lines: Np0(decaying into ee)/Npart • An excess over 0 contribution is seen • Hadron gas interaction • Mean pT of the distribution is lower than the expected QGP contribution Takao Sakaguchi, BNL

  9. Direct photons in p+p collisions • p+p cross-section at s=200GeV is well established with PHENIX Year-5 data set. • Statistically improved from the published Run3 result • Reference for Au+Au collisions • Data parameterized by a fitting function to interpolate to the pT of Au+Au points • Measured p+p yield is higher than NLO pQCD calculation by more than 20%. Data/fit Takao Sakaguchi, BNL

  10. Blue line: Ncoll scaled p+p cross-section Direct photons in 200GeV Au+Au • 900M events • Reached up to 18GeV/c • Qualitatively well described by NLO pQCD calculations Takao Sakaguchi, BNL

  11. RAA with pQCD RAA with p+p data Direct photon RAA in 200GeV Au+Au • Used p+p data is the denominator • NLO pQCD as denominator is shown as well for a reference • For pT<10GeV, RAA is consistent with Ncoll scaled p+p reference. • RAA seems to decrease at very high-pT (especially for central) • Difference of NLO pQCD calculation and p+p data affects quite a bit. Takao Sakaguchi, BNL

  12. Comparison with some models • Turbide et al. (Phys. Rev. C72 (2005) 014906 + Private communication.) • AMY formalism for jet-quenching effect for fragmentation photons. • Systematically data points are below theoretical prediction. • F. Arleo (JHEP 0609 (2006) 015) • High-pT suppression due to isospin effect, in addition to jet-quenching and shadowing. • BDMPS for jet-quenching. • Medium induced jet-photon is not taken into account. • The suppression of very high-pT photon is well reproduced. Takao Sakaguchi, BNL

  13. 100 xT What is expected from structure function? gq ->q is main contribution Au+Au minimum bias Eskola,Kolhinen,Ruuskanen Nucl. Phys. B535(1998)351 Structure function ratios drop by ~20% from x=0.1 to 0.2? Takao Sakaguchi, BNL

  14. What is expected from isospin effect? • Werner Vogelsang provided direct photon cross-section in p+p, p+n and n+n at 200 and 62.4GeV • Minimum bias Au+Au can be calculated by: Takao Sakaguchi, BNL

  15. 100 xT What is RAA for pure hard scattering • Consistent with F. Arleo’s work. • Werner’s comment: The isospin effect has to be bigger than for p0, because for p0 the qg channel is proportional to g(x1)*(u+d+ubar+dbar)(x2), among other things, which is flavor and isospin "blind"… • 62GeV Direct photon would be a good measure of the effect • The effect could be seen in lower pT region, where the analysis is rather established • Interplay of jet-photon conversion and isospin effect in 4-6GeV/c region would be, though One message: RAA<1 for direct photons does not necessarily mean that our message of “p0 suppression at high pT” changes Takao Sakaguchi, BNL

  16. jet fragment photon annihilation compton scattering jet v2 > 0 Bremsstrahlung (energy loss) v2 < 0 Direct photon v2~a photon source detector~ • pT>3GeV/c • N-N and jet fragmentation (v2>0) • Jet-photon conversion, in-medium bremsstrahlung (v2<0) • Higher the pT gets, lower the v2 become. • pT<4GeV/c • Thermal photon v2 based on hydro calculation (roughly 20-30% centrality) • Quark flow ~ photon flow • Dilepton v2 is also predicted, and is in the same order Turbide, et al., PRL96, 032303(2006) Chatterjee, et al., PRL 96, 202302(2006) Takao Sakaguchi, BNL

  17. PHENIX Preliminary sNN=200GeV Au+Au Direct photon v2 in Au+Au collisions • Hadron decay photon subtracted from inclusive photon v2. • Reached up to ~8GeV/c (~4GeV/c in Run2) • Tends to be positive? PHENIX Preliminary sNN=200GeV Au+Au Finalizing systematic errors.. Takao Sakaguchi, BNL

  18. Summary • Direct photons and dileptons are closely related, and can be compensated each other • Can cover broad energy (kinetic) range of EM radiation. • Different production mechanism can be disentangled • Dielectrons in 1-3GeV/c2 is explainable by a charm contribution • An excess in low mass, low pT region is seen in dielectrons • High pT Direct photons in Au+Au reached up to 18GeV/c • Several effects that interplay each other can be disentangled in 62GeV Au+Au analysis • Direct photon v2 is measured up to 8GeV/c • Tends to be positive? • Final results in preparation Takao Sakaguchi, BNL

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