1. 25.01.2007RELNP seminar, ITEP, S.Kiselev1 Direct photons. Data review. Sergey Kiselev, ITEP Moscow  Introduction  Before QM’06 p+p: prompt γ A+B: experimental methods Subtraction method Momentum correlations method Internal conversion method  QM’06 high-p t low-p t elliptic flow v 2 γ-h azimuthal correlation  Conclusions

2. 25.01.2007RELNP seminar, ITEP, S.Kiselev2 Introduction  Direct photons: not from hadron decays  Quark gluon level: qq  gγ, qg  qγ, qq(g)  qq(g)γ. Initial hard NN collisions, pQCD  prompt γ. Thermalised QGP stage  thermal γ from QGP.

3. 25.01.2007RELNP seminar, ITEP, S.Kiselev3 Introduction – cont.  Hadron level: meson scatterings: ππ  ργ, πρ  πγ, πK  K * γ, Kρ  Kγ, KK *  πγ, πK *  Kγ,... Thermalised hadron stage  thermal γ from hadron gas  Decay photons: Long lived (c  » c  AB ~ 50-100 fm) π 0  γγ,   γγ,  ’  ργ/ωγ/2γ Shot lived (c   c  AB ~ 50-100 fm) ω  πγ, a 1  πγ, Δ  Nγ, K *  Kγ,    γ, ρ  ππγ,...

4. 25.01.2007RELNP seminar, ITEP, S.Kiselev4 Prompt  : pp data  A Compilation of Data, J. Phys. G, 23 (1997) A1  Data fit: D.Srivastava, Eur.Phys.J, C22 (2001) 129

5. 25.01.2007RELNP seminar, ITEP, S.Kiselev5 Prompt  : data fit

6. 25.01.2007RELNP seminar, ITEP, S.Kiselev6 Prompt  : other data fit  PHENIX hep- ph/0609037 d 3 σ/dyd 2 p T = (√s) 5 · F(x T,y)

7. 25.01.2007RELNP seminar, ITEP, S.Kiselev7 Prompt  : data/theory P.Aurenche et.al, PR D73, 094007 (2006), with PHENIX, D0 data The data can be described (accuracy ~ 50%) within the NLO QCD (JETPHOX code), except E706 experiment.

8. 25.01.2007RELNP seminar, ITEP, S.Kiselev8 Experimental methods for direct photons  Last years: large progress in experimental techniques to extract direct photons  Direct photons have been revealed by methods: Subtraction method, WA98/2000, PHENIX/2005 Momentum correlation method, WA98/2004 Internal conversion method, PHENIX/2005 External conversion method, PHENIX/2006, QM’06

9. 25.01.2007RELNP seminar, ITEP, S.Kiselev9 Subtraction method  Direct photon measurement by the subtraction method: WA98 PRL 85 (2000) 3595, PHENIX PRL 94 (2005) 232301  WA98 subtracted from measured photons those from known hadronic source: from decays of reconstructed  o, and other hadrons (with some assumption of its yield and spectrum)  At p t > 0,5 GeV/c from  o  from  from  from ’

10. 25.01.2007RELNP seminar, ITEP, S.Kiselev10 Subtraction – WA98

11. 25.01.2007RELNP seminar, ITEP, S.Kiselev11 Subtraction – PHENIX PRL 94, 232301 (2005)

12. 25.01.2007RELNP seminar, ITEP, S.Kiselev12 Momentum correlations method   momentum correlations, WA98 PRL 93 (2004) 022301, STAR nucl- ex/0511055  correlations  direct photons direct photons correlation provide the system sizes at all stages of heavy- ion collisions Needs larger statistics

13. 25.01.2007RELNP seminar, ITEP, S.Kiselev13 Momentum correlations – WA98  R inv (  ≈ 6 fm ≈ R inv (  emitted in the late, hadron gas, stage of the collision Thermal calculations substantialy underestimate the data.

14. 25.01.2007RELNP seminar, ITEP, S.Kiselev14 Internal conversion method  A novel technique (QM’05): internal conversion of direct photons into e + e -, PHENIX, nucl- ex/0511041 any source of real  emits also virtual  with very low-mass  direct   direct   incl. )  incl. Electrons in the central arms were identified by matching charged particle tracks to clusters in the ECAL and to rings in the RICH

15. 25.01.2007RELNP seminar, ITEP, S.Kiselev15 Internal conversion - details Main assumption: the Kroll-Wada (KW) formula, Phys.Rev.98(1955)1355 A given reaction produces, instead of real γ, γ *  e + e -. For decays: N γ – number of real γ π o  γγ π o  γγ *  γe + e - I=  KW = 0.0059 η  γγ η  γγ*  γe + e - I=  KW = 0.0081 γ direct γ* direct  e + e - I=  KW = 0.0162 phase space factor =1, if p ee T » m ee

16. 25.01.2007RELNP seminar, ITEP, S.Kiselev16 Internal conversion – cont.  Measurement for 1 5 it is consistent with a NLO pQCD calculation).

17. 25.01.2007RELNP seminar, ITEP, S.Kiselev17 R AA vs p T for direct photons QM’05: High p T direct photons are not suppressed  strong suppression of mesons is not an initial effect, but a final state effect

18. 25.01.2007RELNP seminar, ITEP, S.Kiselev18 Quark Matter 2006  PHENIX data  High-p T direct photon Hard scattering Talk by T.Isobe  Low-p T direct photon Thermal emission from QGP. Talk by D. Peressounko  Azimuthal anisotropy of direct photon Talk by V.S. Panteuev  γ- h azimuthal correlations Talk by J. Jin  Enter STAR into the game… Run Year Species s 1/2 [GeV ]  Ldt 01 2000 Au+Au 130 1  b -1 02 2001/2 Au+Au 200 24  b -1 p+p 200 0.15 pb -1 03 2002/3 d+Au 200 2.74 nb -1 p+p 200 0.35 pb -1 04 2003/4 Au+Au 200 241  b -1 Au+Au 62 9  b -1 05 2004/5 Cu+Cu 200 3 nb -1 Cu+Cu 62 0.19 nb -1 Cu+Cu 22.5 2.7  b -1 p+p 200 3.8 pb -1 06 2006 p+p 200 93.3 pb -1 ? p+p 62 1.1 pb -1 ? 07 2007 Au+Au 200

19. 25.01.2007RELNP seminar, ITEP, S.Kiselev19 Systematic Study of High-p T Direct Photon Production with the PHENIX Experiment at RHIC Tadaaki Isobe (CNS, Univ. of Tokyo) for the PHENIX Collaboration The 19 th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions at Shanghai, China

20. 25.01.2007RELNP seminar, ITEP, S.Kiselev20 High-p T direct photons: where are we?  p+p: agreement with NLO pQCD.  Run2 high-p T direct photons in Au+Au: consistent with binary scaled NLO pQCD.  Binary scaling is not obvious. 70% prompt photon + 30% jet fragmentation at high-p T. Fragmentation photons are suppressed by jet-quenching effect at RHIC? Compensated by other contribution? 30% contribution from jet frag. Phys. Rev. Lett. 94, (2005) 232301

21. 25.01.2007RELNP seminar, ITEP, S.Kiselev21 Fraction of fragmentation photons  Fraction of fragmentation photons is evaluated in terms of the fraction of isolated photons in 200GeV p+p collisions.  If energy of cone around a target photon is much less than the energy of photon, the photon is defined as isolated photon. Isolation cut removes fragmentation (Bremsstrahlung) photons.  Data are consistent with theoretical expectation within the error. hep-ex/0609031 Jet  Theoretical predictions where PHENIX acceptance is taken into account

22. 25.01.2007RELNP seminar, ITEP, S.Kiselev22 Parameterization of the p+p data  For the calculation of nuclear modification factor, p+p reference is parameterized using a fitting function.  The fitting works well to parameterize the p+p photon data.  The parameterized photon data show enhancement comparing with NLO pQCD expectation by a factor of more than 20%. Data Fit

23. 25.01.2007RELNP seminar, ITEP, S.Kiselev23  Interaction of hard-scattered parton with dense matter. Compton scattering (jet-photon conv.)  R.J. Fries, Phys.Rev. C72 (2005) 041902 Over estimation at high-pT  S. Turbide, Phys.Rev. C72 (2005) 014906 Reproduce data well Bremsstrahlung  B.G. Zakharov, JETP Lett. 80 (2004) 1  If it is observed, it can be used as hard probe of bulk matter. Medium induced high-p T direct photons Jet-quenching effect for fragmentation photons are estimated with AMY formalism. QGP-Thermal Jet-photon NLO-pQCD All Hard scattered parton interacts with gluon in bulk matter

24. 25.01.2007RELNP seminar, ITEP, S.Kiselev24 Direct photon R AA  Nuclear modification factor Yield from hard processes can be scaled with N coll (# of collisions). divided by expected (binary scaled) yield from p+p data.  R AA is consistent with N coll scaled p+p reference.  R AA of very high-p T direct photons is below one. A hint of jet-quenching effect for fragmentation photons? R AA using pQCD shows different tendency. First data using p+p data as reference! Thanks to the more accurate p+p/Au+Au data. R AA with pQCD R AA with p+p data

25. 25.01.2007RELNP seminar, ITEP, S.Kiselev25 Comparison of R AA with theoretical calculation  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-p T 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-p T photon is well reproduced.

26. 25.01.2007RELNP seminar, ITEP, S.Kiselev26 Summary/T.Isobe  Direct photons in 200GeV p+p collisions. Published final year-3 p+p data. Preliminary year-5 data. Consistent with NLO pQCD within uncertainty.  Direct photons in 200GeV Au+Au collisions. Clear signal of direct photon at high-p T thanks to the strong suppression of neutral hadrons. Spectra up to 20GeV/c.  First direct photons R AA in 200GeV Au+Au collisions with p+p reference. Almost consistent with binary scaled p+p data. R AA seems to be below one at very high-p T region.

27. 25.01.2007RELNP seminar, ITEP, S.Kiselev27 Direct photons at low p t measured in PHENIX D.Peressounko RRC “Kurchatov institute” for the PHENIX collaboration

28. 25.01.2007RELNP seminar, ITEP, S.Kiselev28 Subtraction and Tagging methods  Measure photon spectrum and remove those photons which make  0 mass with any other  Correct direct photon candidate sample for contribution from  0 decay photons with missing partner and for direct photons with fake partners  Subtract contribution from ,  etc. decays  Measure yield of inclusive photons corrected for hadron contaminations, conversion, efficiency and acceptance.  Measure spectrum of  0, ,  etc.  Calculate yield of decay photons and subtract it from the inclusive yield. N  dir = N  incl - N  decay Subtraction Tagging

29. 25.01.2007RELNP seminar, ITEP, S.Kiselev29 d+Au collisions: Double ratio Internal conversion method provides smaller systematic errors But not as small as in the case of Au+Au collisions in Run-4 ( Large background of external conversion on MVD detector in Run-3)

30. 25.01.2007RELNP seminar, ITEP, S.Kiselev30 d+Au collisions: Spectrum Internal conversion extends range of significant points to p t > 2 GeV Data agrees with pQCD predictions in full p t range => No indication for nuclear effects

31. 25.01.2007RELNP seminar, ITEP, S.Kiselev31 Au+Au collisions: External conversion  Combining this photon with others measured in EMCAL with loose PID cut, estimate proportion of photons coming from  0 decays  Correct for missing  0 decay partners  Subtract , , ’ decay photons  Calculate ratio N  all /N  decay  Use very tight PID cut on EMCAL photons to produce very clean photon sample  Use external photon conversion in beam pipe to produce very clean photon sample External conversionTagging no pair cut with pair cut Dalitz Conversion Uses very pure photon sample avoid explicit calculation of  0 spectrum =>reduce systematic errors

32. 25.01.2007RELNP seminar, ITEP, S.Kiselev32 Comparison: Au+Au, central collisions Spectra agree within errors in entire p t range Systematic errors are still too large to extract thermal photons. There is room for thermal photons This is consistent with excess above pQCD reported previously

33. 25.01.2007RELNP seminar, ITEP, S.Kiselev33 Two-photon correlations 11 22 11  2 rec e-e- e+e+ External conversion: No close cluster interference No hadron contamination C 2 calculated in EMCAL and converted+EMCAL agree => both effects are under control

34. 25.01.2007RELNP seminar, ITEP, S.Kiselev34 Conclusions/D.Peressounko  Measurement of direct photon yield at small p t is very interesting but extremely complicated task  PHENIX has developed a variety of methods for direct photon extraction in p+p, d+Au and Au+Au collisions producing consistent results  Because of the large systematic errors comparison of binary scaled d+Au spectrum with Au+Au does not allow to make a statement on the origin of the excess above pQCD observed in Au+Au.  More precise data are coming…

35. 25.01.2007RELNP seminar, ITEP, S.Kiselev35 PHENIX measurements of reaction plane dependence of high p T photons and pions in Au+Au collisions Vladislav Pantuev, University at Stony Brook for PHENIX collaboration

36. 25.01.2007RELNP seminar, ITEP, S.Kiselev36 Compton Annihilation In p+p Hard photons: direct component Photons in A+A Direct PhotonsDecay Photons hardthermalhard+thermal QGPHadron gasdirectfragmentation Preequilibrium photons jet-  - conv. Medium induced  bremsstr. In A+A picture is much more complicated: V2=0 V2<0 V2>0

37. 25.01.2007RELNP seminar, ITEP, S.Kiselev37 There are theoretical predictions with a sizable azimuthal parameter v 2 : S.Turbide, C.Gale, R.J.Fries, PRL 96 032303 (2006) R. Chatterjee et al., PRL 96, 202302 (2006) Thermal photons are produced throughout the expansion history and reflect quark anisotropy Jets lose more energy where the medium is thicker - more jet-photon conversions (v2 0) 4

38. 25.01.2007RELNP seminar, ITEP, S.Kiselev38 How does PHENIX measure direct photons and v 2 ?  Measure inclusive photon yield, N inc  Measure hadron contribution components  0 and   By Monte Carlo calculate   and  decay background in inclusive sample, N bg  Calculate direct photon excess over hadron decays, R  Measure inclusive and hadron v 2 by reaction plane method  Calculate direct photon v 2 as R * v 2 inc – v 2 BG R = N inc / N BG v 2 dir = R – 1 Use large statistics Run 4 Au+Au data set See also poster 86 by Kentaro Miki 5

39. 25.01.2007RELNP seminar, ITEP, S.Kiselev39 Step by step calculations: PHENIX preliminary 6

40. 25.01.2007RELNP seminar, ITEP, S.Kiselev40 PHENIX direct photon v 2 result Within statistical and systematic errors v 2 is consistent with zero. v 2 =0 or cancellation of different contributions? Systematic errors dominantly from R: Enormous background of decay photons at low p T 7

41. 25.01.2007RELNP seminar, ITEP, S.Kiselev41 PHENIX Measurement on High p T h-h and -h Azimuthal Correlations Jiamin Jin For the PHENIX collaboration Quark Matter 2006, Shanghai Nov. 18, 2006

42. 25.01.2007RELNP seminar, ITEP, S.Kiselev42 Method  Construct inclusive -h yield  Construct decay -h yield via: Pair by pair weighted summation  convolutes all  0 -h pair contributions from higher p T  Weight reflects probability from kinematics for  0 at given p T to decay into photon in given p T range  Subtraction via:    # inclusive   #  decay  p+p R=

43. 25.01.2007RELNP seminar, ITEP, S.Kiselev43 First direct -h yield in p+p, cmp with PYTHIA! p+p: important baseline measurement! data PYTHIA PYTHIA 6.1 k T = 2.5 GeV A nice confirmation of our method PHENIX Preliminary

44. 25.01.2007RELNP seminar, ITEP, S.Kiselev44 v 2 modulated bkgd for inclusive/decay  subtracted from each corr. fn under ZYAM assumption (v 2 from single  measurements) Near side yield consistent with 0  small fragmentation photon yield Away side yield also small, suppressed!? Au+Au: study medium induced modification! First direct -h yield in Au+Au! 1/N trig dN/d   (rad) 1/N trig dN/d 

45. 25.01.2007RELNP seminar, ITEP, S.Kiselev45 Comparison btw Au+Au and p+p Hint of away side modification in AuAu! Black: Au+Au Red: p+p 1/N trig dN/d   (rad) 1/N trig dN/d   (rad)

46. 25.01.2007RELNP seminar, ITEP, S.Kiselev46 Away side integrated yield trigger  p T dependence assoc. h p T dependence centrality dependence + pp p+p shows a systematic trend of having higher yields in the away side than Au+Au!

47. 25.01.2007RELNP seminar, ITEP, S.Kiselev47 Conclusions/J.Jin  First measurements of high p T direct -h yields in Au+Au/p+p collisions Near side yield ~ 0 Hint of suppression of away side jets in Au+Au Need more statistics to make conclusive statement  Upcoming Au+Au run

48. 25.01.2007RELNP seminar, ITEP, S.Kiselev48 Conclusions  High-p t : R AA in 200GeV Au+Au collisions seems to be below one at very high-p T region.  Low-p t : more methods, but errors are still too large. More precise data are coming…  Elliptic flow v 2 : within statistical and systematic errors v 2 is consistent with zero.  γ-h azimuthal correlations: near side yield ~ 0, hint of suppression of away side jets in Au+Au, need more statistics.  Multi-purpose Direct Photons