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Direct photons and their Flow measured by PHENIX

Direct photons and their Flow measured by PHENIX. Kensuke Okada f or the PHENIX collaboration RHIC-AGS Users meeting June 12, 2012. Direct photon: a unique probe. high pT: Known source, Penetrating probe A good reference to jet quenching low pT : QGP production mechanism

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Direct photons and their Flow measured by PHENIX

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  1. Direct photons and their Flow measured by PHENIX Kensuke Okada for the PHENIX collaboration RHIC-AGS Users meeting June 12, 2012

  2. Direct photon: a unique probe • high pT: Known source, Penetrating probe • A good reference to jet quenching • low pT: QGP production mechanism • Spectra : A thermometer • Azimuthal dependence to the reaction plane : Probe for the formation mechanism A new state of the matter (sQGP) Produced by HI collision.

  3. PHENIX detector The central arm spectrometer Fine segmented EMCal Electron identification, tracking + High DAQ rate Trigger

  4. Reference data (p+p) arXiv:1205.5533 Measured up to pT=25 GeV/c. The pQCD NLO calculation is in good agreement with data. The pT range in the previous report. (PRL 2007)

  5. xT scaling arXiv:1205.5533 pp/p+pbar, inclusive/isolated PHENIX e+e- xT2pT/s cross section scaled by s4.5 PHENIX  PHENIX  (PRL 2007) They are on a universal curve except two experiments, from LHC to fixed target experiments. n=4.5 is in a range consistent with expectations from NLO pQCD.

  6. Study of the event shape arXiv:1205.5533 Direct photon (0.1*E>Econe) Checked the event shape with an isolation cut. Generally the theory calculation agrees with data. At high pT most direct photons are isolated.

  7. Study of the event shape arXiv:1205.5533 Direct photon (0.1*E>Econe) Photon from 0 Checked the event shape with an isolation cut. Generally the theory calculation agrees with data. At high pT most direct photons are isolated.

  8. Direct photon in AuAu 200GeV high pT PRL94,232301 (2005) (Run2) arXiv:1205.5759 (Run4) There is more than X10 statistical improvement.  It allows to study the RAA as a function of pT.

  9. Direct photon RAA arXiv:1205.5759 Minimum bias 0-5% 60-92% L in p+p Ncoll RAA~1 : Consistent with binary scaling of p+p. However there are Isospin difference, nPDF, suppression of fragment photon, etc.

  10. Comparisons with models arXiv:1205.5759 0-5% • Initial state effects (IS) include isospinand nuclear PDF, consistent with data • Final state effects (FS) include suppression of jet fragmentation photons and photons from jet-plasma interaction, consistent with data • Another model with both IS and FS disagrees with data • JHEP1104, 055 PRC77, 024909 arXiv:0904.2184 • PLB669, 337

  11. Direct photon in d+Au for CNM Run8 Run3 Rd+Au is consistent with 1. It suggests little or no nuclear effect within our uncertainty.

  12. d+A Sensitive to gluon PDF We have x30 statistics in Run8 compared to Run3. It help constrain the gluon PDF further. arXiv:0902.4154 (gluon) arXiv:1012.1178 x=0.1 10GeV photon in s=200GeV HardProbes (Helenius,Eskola) What if ?

  13. Photon = e++e- low pT e+ They have the same quantum number. q e- g* Kroll-Wada formula connects the real  and (ee) yield. g q , S=1 for photons. When Independent of the origin in the very low mass region (Mee < ~30MeV) No 0 Dalitz above the 0 mass.  The key to improve the S/N ratio. Direct photon follows 1/Mee. Procedure Combinatorial and correlated pair subtraction Cocktail and direct photon shapes Normalized in the very low mass region Fit and Extract the direct photon component m

  14. Virtual photon spectra PRL 104,132301 (2010) Au+Au p+p: Already shown in the previous xT plot. d+Au: Consistent with scaled p+p. Little or no nuclear effects. Au+Au: Large excess in low pT region. <T> is extracted from the inverse slope.

  15. Initial temperature & formation time PRC 81, 034911 (2010) Tc~170MeV from lattice QCD They are all above the critical temperature. However Tinit depends on 0 in the theory calculations.  Need additional experimental constraints

  16. Direct photon 2 (another knob) v2 < 0 Parton+medium v2= 0 Hard scattering q+g sQGP Hadron gas v2 > 0 Jet fragment v20 Amplitude for 0,Relative ratio pT The ingredients are tuned by pT Parton+medium Hadron gas Hard scat. sQGP Jet fragment

  17. Direct photon 2 From real photon in the EMCal with virtual photon measurement Inclusive photon v2 BG photon v2 (From 0 and other mesons v2) From virtual photon measurement

  18. Step 1,2,3 PHENIX arXiv:1105.4126 Min bias events Decay, other hadrons

  19. Step 1,2,3 and confirmation Min bias events PHENIX arXiv:1105.4126 Confirmed by the external conversion method External conv. EMCal photon (No charged hadrons, no secondary interactions) e e HBD backplane

  20. Direct photon 2 arXiv:1105.4126 calculation from PRC 79, 021901(R) 20-40% 0-20% MB (0-92%) At high pT, v2~0. It is consistent with the hard scattering source. At low pT (thermal region), an unexpectedly large v2 is observed! early  late  small  large It depends on the formation time. But theory predictions are too small.

  21. Next step: 2 of virtual photon sys. uncertainty table arXiv:1105.4126 Advantage (systematic) real photon v2 from combinatorial BG and remaining Dalitz decay can be well controlled. Disadvantage (statistics) Total statistics goes down by a factor of ~200. Even in 1-3 GeV/c bin, it’s statistically challenging. virtual photon • ee are induced in a strong magnetic field in HI collisions? PRC 83, 017901 (2011) Tuchin If it is true, it affects the assumptions in all virtual photon results. Anyway it is interesting.

  22. PHENIX upgrade for photons MPCEX 3.1<h<3.8 To be ready for Run-14 • A combined charged particle tracker and EM preshower detector – dual gain readout allows sensitivity to MIPS and full energy EM showers. • Charged track identification • p0 reconstruction out to >80GeV Measure the Gluon Distribution in CNM at Low-x Direct photons (h, 0 suppression + isolation cut)

  23. Future sPHENIX project A plan to upgrade the detector. Large acceptance with high /0 separation. More tracking layers, hope eID is still powerful. Hadron calorimeter for +Jet analysis. RHIC Upgrade Workshop (June 13, morning)

  24. Summary • p+p reference measurements are on the universal curve of world’s measurements. • No nuclear modification (RAA~1) is seen in high pT photon. • An unexpectedly large 2 was measured in the low pT region. No theoretical explanation exists so far. • PHENIX upgrade plan is on the table.

  25. Backup

  26. Space time evolution

  27. Hadron contamination check • Hadron contamination can be significant • Check with an external conversion analysis • Identify photons via conversion in material to dileptons • No hadron contamination • Two measurements are consistent • Hadron contamination in the real photon (EMCal) measurement well understood

  28. STAR

  29. STAR vs PHENIX They are not so different. Doesn’t STAR have more combinatorial from conversions? They can be eliminated so well?

  30. PHENIX Au+Au Statistics In Run10, 11, the integrated luminosity is comparable to Run7. Can we remove Dalitz decay to reduce the combinatorial? Then small Mee will be cut out. It needs some trick for the mass shape fit. STAR has an advantage if their claim for the combinatorial BG is true.

  31. RHIC advantage to LHC

  32. System size dependence of g fraction • g fraction = Yielddirect / Yieldinclusive • Largest excess above pQCD is seen at Au+Au. • Moderately in Cu+Cu also. Excess also in Cu+Cu No excess in d+Au (no medium)

  33. Comparison with models. No success.. • Later thermalization gives larger v2 (QGP photons) • Large photon flow is not explained bymodels for QGP Hydro after t0 Curves: Holopainen, Räsänen, Eskola., arXiv:1104.5371v1 QM: Quark Matter HM: Hadronic Matter thermal diluted by prompt  Chatterjee, SrivastavaPRC79, 021901 (2009)

  34. ppg126 statistics AN870 Nevt=3*109 2 1-2GeV (MB) N= 2*2*3*109*0.7 = 2.6*1010 10GeV N= 5*10-6*2*3*109*0.7=6.6*104 5*10-6 3300/bin  1/3300=1.7% consistent. 0.001/0.05=2% Fig.3.14 Fig.3.17

  35. virtual photon statistics estimation real  virtual  0.135<Mee<0.3 1  *0.01  *0.16 Dilution for e+e-, 1<pT<2 GeV/c, Mee>0.135 (S’+Bcomb)/S’ = 10 S’= Sdir + Shad (Sdir + Shad)/Sdir= 2 total 1:20

  36. Statistical uncertainty statistical uncertainty (if v2had is well known) 2v2obs*RP Run7 , 1 bin (1-2GeV), v2dir=0.15, RP=0.3

  37. Run7 virtual photon v2 estimation real + negligible statistical error virtual + ~3% statistical error (Run7) Systematic of R is 3.1% (relative) from virtual photon result. So the S/(S+B) for the virtual photon is measured at this level. key: statistics, S/B from combinatorial BG

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