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Profiling high pT direct photons

Profiling high pT direct photons. Takao Sakaguchi Brookhaven National Laboratory. Aren’t you the guy that tells me?. Give me logistics before taking me out. Finally found? How does it look like?. Contents. Direct photon basics Direct photons in p+p at 200GeV

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Profiling high pT direct photons

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  1. Profiling high pT direct photons Takao Sakaguchi Brookhaven National Laboratory Aren’t you the guy that tells me? Give me logistics before taking me out.. Finally found? How does it look like? Takao Sakaguchi, BNL, for RHIC/AGS 07

  2. Contents • Direct photon basics • Direct photons in p+p at 200GeV • Direct photons in d+Au at 200GeV • Direct photons in Au+Au at 200GeV • Direct photons in Au+Au at 62.4GeV • Direct photons elliptic flow in Au+Au at 200GeV • Summary Takao Sakaguchi, BNL, for RHIC/AGS 07

  3. direct fragment Direct photon production ~basics~ • 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 High pT direct photons produced in the initial stage Takao Sakaguchi, BNL, for RHIC/AGS 07

  4. Hard scattered partons interact with thermal partons in matter Sources of photons (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, for RHIC/AGS 07

  5. Quick silver bullet Cartoon only: sources of g, mean pT vs time (dashed: hadrons) hard scatt pT (GeV) jet Brems. All we can see is the projection to this axis with the dashed sources as background dominated up to medium pT by this jet-thermal jet fragmentation sQGP hadron gas hadron decays log t 1 10 107 G. David, HP06 (fm/c) Takao Sakaguchi, BNL, for RHIC/AGS 07

  6. 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 ~20%. Data/fit T. Isobe, QM06, K. Okada SPIN2006. Takao Sakaguchi, BNL, for RHIC/AGS 07

  7. RHIC data among the world • A compilation with world data • P. Aurenche et al. PRD73(2006)094007 Takao Sakaguchi, BNL, for RHIC/AGS 07

  8. Primary (hard scattering) photons vs. photons associated with jets (fragmentation, FS hadron decay) Calculable, and reasonable agreement with data even if the usual 0.5 cone is near PHENIX’s limit How well do we know about fragment photons? ~from p+p~ Jet g PHENIX, PRL98, 012002(2007) Well described by a NLO pQCD at high pT -> some idea on fragment contribution Takao Sakaguchi, BNL, for RHIC/AGS 07

  9. Direct photons in d+Au (PHENIX) NLO pQCD Calculation p+p collisions Calculated by W.Vogelsang CTEQ6M Scale(renormalization and factorization scale) 0.5,1.0,2.0pT In comparison with d+Au Averaged number of collisions (8.42) from the Glauber model was multiplied to the calculation. “EMC effect” for gluons TS comment: tend to decrease at high pT? G. David, HP06 Takao Sakaguchi, BNL, for RHIC/AGS 07

  10. Double ratio in d+Au (STAR) R = 1 + dir / decay • incl in same dataset as 0 • signal consistent with pQCD NLO calculation • further reduction of error bars needed for dir calculations by W. Vogelsang both data and calculation include contribution from fragmentation photons sizeable fragmentation contribution M. Russcher (STAR), QM06 Takao Sakaguchi, BNL, for RHIC/AGS 07

  11. 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 T. Isobe, QM06 Takao Sakaguchi, BNL, for RHIC/AGS 07

  12. 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. T. Isobe, QM06 Takao Sakaguchi, BNL, for RHIC/AGS 07

  13. 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. T. Isobe, QM06 Takao Sakaguchi, BNL, for RHIC/AGS 07

  14. 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, for RHIC/AGS 07 Priv. Comm with M.J. Tannenbaum

  15. What is expected from isospin effect? • Direct photon cross-section for p+p, p+n and n+n are different because of different charge contents (eq2) • Effect can be estimated from NLO pQCD calclation of p+p, p+n and n+n • W. Vogelsang, priv. comm. • Minimum bias Au+Au can be calculated by: (sAA/Ncoll)/spp vs pT (sAA/Ncoll)/spp vs xT The effect will be seen in lower pT at sNN=62.4GeV T. S., WWND07 Takao Sakaguchi, BNL, for RHIC/AGS 07

  16. New! ~62GeV Au+Au Direct photons~ • First direct photons spectra in 62.4GeV Au+Au collisions • pT extended to 7.5GeV/c, which is equivalent to 24GeV/c at 200GeV in terms of xT(= 2*pT/s) T. S., INPC07 Takao Sakaguchi, BNL, for RHIC/AGS 07

  17. New! ~62GeV Au+Au Direct photons~ • Direct photon over NLO pQCD is consistent with unity at 62.4GeV • p+p reference can not be well-defined. Needs a measurement at RHIC 0-10% 10-30% 30-60% Min Bias T. S., INPC07 Takao Sakaguchi, BNL, for RHIC/AGS 07

  18. Recall data to NLO pQCD at 200GeV p+p data over fit, NLO over fit (200GeV) • The ratio of p+p data to NLO pQCD is ~ 1.2 at 15GeV/c at sNN=200GeV • If p+p data at 62.4GeV is higher than NLO pQCD similarly as 200GeV, ~1.2 is expected at ~5GeV/c • pT scaled by 62.4/200 (xT-inspired scaling) • If we take this baseline, the isospin effect is seen at 62.4GeV at this pT region! T. S., INPC07 Takao Sakaguchi, BNL, for RHIC/AGS 07

  19. 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, for RHIC/AGS 07

  20. 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.. K. Miki, QM06 Takao Sakaguchi, BNL, for RHIC/AGS 07

  21. Summary • High pT direct photons are measured in various systems and energies. • Now the quantity is at a precise evaluation stage • Direct photon v2 could disentangle the source of photons I love wondering! Long way… Takao Sakaguchi, BNL, for RHIC/AGS 07

  22. Backup Takao Sakaguchi, BNL, for RHIC/AGS 07

  23. Direct g and p0 nuclear modification factor RdA in d+Au Both g and p0 consistent with 1 Takao Sakaguchi, BNL, for RHIC/AGS 07 Hard Probes 2006, June 15, 2006 – G. David, BNL

  24. 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, for RHIC/AGS 07

  25. 100 xT “EMC effect” for gluons Nuclear Modification Factor Consistent with 1  No modification within the error This is first measurement of ‘EMC effect’ for gluons Takao Sakaguchi, BNL, for RHIC/AGS 07 Hard Probes 2006, June 15, 2006 – G. David, BNL

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