Illuminating RHIC Matter with the Multi-purpose Direct Photon

1. Illuminating RHIC Matter with the Multi-purpose Direct Photon Justin Frantz (A member of PHENIX on behalf of RHIC) Quark Matter’ 06 Shanghai, China November 16th, 2006

2. Intermediate pT Jet-medium Greater Picture Pseudo-Cronological Progression of Direct Photon Theory/Studies/Measurements in HI A healthy and expanding sub-field ! Soft Spectrum Hard Spectrum QGP/Hadron Thermal pQCD/Jet Suppression Control Intermediate pT Jet-medium v2 Control (0!) g-h (jet) Rates g-g HBT Virtual g Di-photons? g-jet Shapes Forward g CGC Direct Photon v2? time Multi-purpose!!! Justin Frantz Quark Matter ’06

3. Greater Picture Pseudo-Cronological Progression of Direct Photon Theory/Studies/Measurements in HI A healthy and expanding sub-field ! Soft Spectrum Hard Spectrum QGP/Hadron Thermal pQCD/Jet Suppression Control Intermediate pT Jet-medium v2 Control (0!) g-h (jet) Rates g-g HBT Virtual g Di-photons? g-jet Shapes Forward g - CGC Non-0 Direct g v2? time Multi-purpose!!! Justin Frantz Quark Matter ’06

4. Other Uses (Deprecated)… • Many bad puns • e.g. “Illuminating” RHIC Matter with the Multi-purpose Direct Photon - Justin Frantz QM06 -Charles Gale hep-ph/0609301 Justin Frantz Quark Matter ’06

5. How Use _ FUL _? • Now into the first years of the post-celebritory (we found the signal!) phase… • ..What have we learned from direct photons at RHIC so far? (pre QM’06) • For now, in most cases it is driven by precision scale… • Low Precision: Qualitative Result @ low pT thermal photons are probably present (almost as much as WA98) • Better Precision: Quantitative Result: At high pT prompt Direct photons binary scale to within ~+/-20% Justin Frantz Quark Matter ’06

6. The question of precision • So far most direct g theoretical predictions cannot be tested with any stringency due to low precision • Some recent improvements in measurement techniques as well as new avenues proposed by theory and experimentalists alike have shown promise in rectifying this situation. • This QM reveals concrete (quantitatively tangible) experimental steps made in nearly all available directions • Allows us to: • in a few cases, add some items to “learned at RHIC” • See what, in more definite terms, we will be able to learn in the next several years • To this end, in this talk I will try to lay out quantitative estimates where I can Justin Frantz Quark Matter ’06

7. Start w/ Low pT Precision… • Published PHENIX Result: • Calorimeter Result, statistical “cocktail” comparison • Double Ratio R = gtot/gdec • = 1+ Sdirect/Bdecay • Absolute precision on gdir degrades as S/B decreases, R ~ 1 • Only upper limits constrained within 12% R systematics.. Justin Frantz Quark Matter ’06

8. Still Many gtherm Models Possible • Thus the theoretical predictions cannot be constrained… • Complete models generally include: QGP/ Hadronic Gas Rates, folded w/ hydrodynamic volume, EOS Assumption, Initial state (ie Ti) choices • Renk (2004) w flow/HBT HHG important Ti=110 MeV • d’Enterria & Peresseunko (2005) w/ periph. Ti=610 • Bass,Renk,Sriv., et.al. (2004) PCM Only (no thermal) • Turbide, Gale, Rapp (2004) HHG not important Ti= 370 • Gelis, Neimi, et.al. (2003) Ti=580 • Alam, Sinha, et.al. (2001) Ti = 265 • Srivastava (2001) Ti390-670 • … • … Most Complete? Justin Frantz Quark Matter ’06

9. Still Many gtherm Model Possible • Renk (2004) w flow/HBT HHG important Ti=110 MeV • d’Enterria & Peresseunko (2005) w/ periph. Ti=610 • Bass,Renk,Sriv., et.al. (2004) PCM Only (no thermal) • Turbide, Gale, Rapp (2004) HHG not important Ti= 370 • Gelis, Neimi, et.al. (2003) Ti=580 • Alam, Sinha, et.al. (2001) Ti = 265 • Srivastava (2001) Ti390-670 Not well constrained (hence the continuing proliferation of models) Justin Frantz Quark Matter ’06

10. Direct Photon Precision/Accuracy in General (e.g. Particle Physics) • Experience tells us more than 1 experiment cross checking is good D0 CDF From Peitzmann and Thoma: Physics Reports 364 (2002) 175–246 Justin Frantz Quark Matter ’06

11. QM’06: Enter STAR into the game… • PHENIX has 2 calorimeters, but still same experiment (sharing aspects of clustering/ data analysis/ triggering) • sE/E = 8%/√E + 2%,DpDh seg = 0.01, |h| < 0.35 • Great to have independent confirmations from STAR • STAR Calorimeter: • sE/E = 16%/√E + 2%, • DpDh seg = 0.05, w/ a shower max detector 0.007 • 0< h < 1 Justin Frantz Quark Matter ’06

12. 2 Experiments: ~√2 x the Precision? • Also good for averaging completely indep. measurements to reduce errors a la PDG d+Au 200 GeV PHENIX Preliminary Now: Errors in 6-10 GeV Region STAR 16% PHENIX 12% -- combined: 9.5 % In the future?: STAR 10% PHENIX 8% -- combined 6% STAR p+p well underway as well (Martijn Russcher talk) Justin Frantz Quark Matter ’06

13. Improving Precision: Low pT • Calorimeter measurements limits: • Resolution gets worse @ low pT • Hit clustering problems (splitting/merging) • Turn to several other methods • External Conversion Methods • New: Internal Conversion Method • HBT EMCal Tracking e+ e- sE/E Resolution (%) pT (GeV/c) Justin Frantz Quark Matter ’06

14. Photon Conversion Method • Identify conversion pair candidates • STAR two-track vertices • PHENIX mis-rec’d mom-- Mass peak @ 0 moes to finite mass • Electron systematics same or smaller than EMCal • Bkg. Norm. easier (di-electron ~< 1% syst.) • Better Mom resolution @ low pT • Abs. efficiency more difficult • Independent measurement (error reduction) STAR TPC PHENIX Beam Pipe r Run4 data r = mass vs f Justin Frantz Quark Matter ’06

15. New Result / Old Result • First PHENIX Result Using this method: Au+Au 200 GeV “Old” STAR 130 GeV Au+Au Result New PHENIX Result this week! Talk by D. Peresseunko Full Decay Photon Calculation not included :nucl-ex/0401008 What happened? looked promising. Justin Frantz Quark Matter ’06

16. Internal Conversion Method • Y. Akiba (PHENIX), Inventor • All real photon sources make virtual photon e+e- pairs • Measure e+e- in mass region where direct should dominate over Dalitz →convert to total excess of direct g* over Dalitz • Au+Au Result from last QM’05 • Method applied to d+Au • Feasibility in lower multiplicity • Need reference esp. @ low pT where soft may not != pQCD Justin Frantz Quark Matter ’06

17. Virtual g = Real g? • Theoretical Uncertainty • e.g. g* longitudinal states • Answer by going to even higher pT looking for consistency w/ high pT calorimeter/(conversion) result • Next factor of 5-10 in statistics should do it • Also repeat in p+p (w/o possible nuclear effects) Justin Frantz Quark Matter ’06

18. @ Very low pT : g-g HBT • Several theoretical works: important not just for direct photon yield • Direct Yield can be obtained from strength of HBT Qinv peak • STAR prelim result QM’05: detector effects? • PHENIX work on this also… Justin Frantz Quark Matter ’06

19. To Intermediate pT:The Kink • There is kink in both the run2 and run4 datasets in the same place… Au+Au 200 GeV Run2 Final PHENIX Final Run4 Au+Au 200 GeV This could easily just be a systematic effect but it is at least a little curious b.c. it’s not there in other centralities Justin Frantz Quark Matter ’06

20. Jet-Medium Photons: Two Types • g-jet Conversion • Model: q jets traversing q/g bath convert (Kinematics: small u dominates: pg ≈ pq) First calc Fries, et. al./ more complete treatment w/ Turbide,Gale et. al. • Fragmentation (Brems.) g • Jet Eloss implies suppression of Frag g but Zakarov/others predict enhancement (New paper from E. Wang et. al.) also included by the above authors. w/o suppresion Justin Frantz Quark Matter ’06

21. Jeon, Jalilian-Marian, Sarcevic nucl-th/0208012 Jet-Medium Photons Two pT Regions • Fragmentation (Brems.) g-jet Conversion Imply large (2x) at Intermediate pT • But also as importantly out to the highest pT: no suppression! • i.e. wins out over expected jet suppression Justin Frantz Quark Matter ’06

22. Direct Photon v2 • Jet-medium sources /(& jet suppression also should cause non-zero direct g v2 • Measure the Reaction Plane fR, Particle production at (f – fR) → v2 • PHENIX Paper: Indications of direct photon in inclusive (decay + direct) g flow? • QM’06 STAR Poster on this as well (G.Lin) • Jet-medium interactions -> non-0 v2 (admixture includes negative) PHENIX nucl-ex/0508019 Justin Frantz Quark Matter ’06

23. In 40-60% disagreement above 3 GeV—all points positive 0-20% also disfavors though slightly Still inconclusive within the PHENIX uncertainties? First measurement: Run 7/8 Au+Au systematics reduceable Direct Photon v2 Turbide, et.al PHENIX Preliminary PHENIX Preliminary Justin Frantz Quark Matter ’06

24. In order to test the rates… • Better p+p reference needed to make definitive statement • In past Au+Au “fake” RAA w/ NLO pQCD • More precise Run5 PHENIX now available, also work from STAR in this direction p+p→gdirect+X p+p→p0+X Justin Frantz Quark Matter ’06

25. PHENIX Au+Au High pT Data • With new p+p PHENIX makes real direct g RAA … PHENIX Parallel talk by TadaAki Isobe Justin Frantz Quark Matter ’06

26. Jet-medium Enhancement Tested… • …allowing a quantative test of Jet-medium enhancement predictions • At mid pT some enhancement may be possible, but current predictions are strongly disfavored Justin Frantz Quark Matter ’06

27. Jet-medium Enhancement tested… • …allowing a quantative test of Jet-medium enhancement predictions • At high pT data favors standard suppression predictions, not enhancement Justin Frantz Quark Matter ’06

28. Implications/Discussion • Homework for theory: • Bremstrahlung enhancement must exist (in however small amount) if gluon radiative Eloss (GLV, BDPMS…) is present • can discrepancy be accounted for? Another constraint on radiative picture? • g-jet conversion seems reasonable given a QGP, where does it go wrong? (modified aS…) • Interpretation of the partonic medium? • Is there suppression in high pt gdirect? Still need more precision at high pT Justin Frantz Quark Matter ’06

29. Other (deprecated) uses of RHIC g, continued… • Bad alliterative experiments… • “Phun with Photons” ???? Justin Frantz Quark Matter ’06

30. Photon-Jet Has Arrived!!! • 2 particle Df Correlations • Both STAR and PHENIX: First results p+p • PHENIX Au+Au Result, STAR work on d+Au • Au+Au g signal cleaner p+p/d+A jet signal cleaner • 2 Parallel Talks: Subhasis Chattopadhyay, Jiamin Jin g-jet jet-jet C(Df) p p 0 0 PTassoc. hadron > 1 GeV/c STAR d+Au Preliminary Justin Frantz Quark Matter ’06

31. g-jet in Au+Au • PHENIX Au+Au compared to p+p See also poster by Matt Nguyen Justin Frantz Quark Matter ’06

32. Gamma-Jet Yields • Integrated Away-side yields: • STAR/PHENIX p+p yields roughly consistent (STAR trigger bin higher) • PHENIX Au+Au consistent with expected suppression! • Next step, more precision, take Au+Au/p+p ratio (IAA) p+p Justin Frantz Quark Matter ’06

33. What will we now learn from g-jet? • Cleaner determination of fragmentation modification ~ better constrain Eloss models F. Arleo hep-ph/0601075 IAA w/ Eloss Trigger g don’t have surface bias, thus eventually should constrain Eloss geometry Justin Frantz Quark Matter ’06

34. Most Important Use of Direct g • Fitting the direct photon data into the overall picture we are constructing at RHIC… Justin Frantz Quark Matter ’06

35. Summary • Full entrance of STAR into RHIC direct g measurement will be and in fact is already beneficial • Need for greater precision at low pT being addressed with new measurements/methods • New methods being employed: external (PHENIX/STAR), internal (PHENIX) conversion methods, HBT (PHENIX/STAR) • Cold matter references have likewise already been improved • New RAA data (PHENIX) strongly disfavors large jet-medium enhancements @ intermediate pT (4-5 GeV/c)… • …& favors “standard” gfrag suppression, disfavors enhancement to the highest pT’s • Direct g flow measurements inconclusive: but also favor “standard” gfrag suppression more than jet-medium • First measurement of p+p gdirect-jet 2-particle corr.’s • Within large error bars we see the suppression effect • Improved precision will allow quantitative study Justin Frantz Quark Matter ’06

36. d+Au Internal Conversion • pQCD not trusted at low pT • There could be photon production from soft physics in p+p/ p+A • ~no theoretical guidance on this • Thus reference result for low pT photon production needed Justin Frantz Quark Matter ’06