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RHIC Hard and Soft Photon Probes in PHENIX

This paper discusses the progression of direct photon theory, studies, and measurements in heavy-ion collisions. It explores the different views of QCD interactions and provides insights into the properties of QGP and hadronic matter.

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RHIC Hard and Soft Photon Probes in PHENIX

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  1. RHIC Hard and Soft Photon Probes in PHENIX Justin Frantz QNP’ 06 Madrid, Spain June 6th, 2006 Status, New/Near Future Results & Improvements, Directions

  2. Intermediate pT Spect. Jet-medium Greater Picture Pseudo-Cronological Progression of Direct Photon Theory/Studies/Measurements in HI A healthy and expanding sub-field ! BASIC IDEA: EM g provides clean/different view of QCD interactions/matter Soft Spectrum Hard Spectrum QGP/Hadron Thermal Rates/Info pQCD/Jet Suppression Control Intermediate pT Spect. Jet-medium g-h (jet) Rates Hadron v2 Control g-g HBT rates + spacial info g-jet Correlation Shapes Di-photons Forward Prod CGC Virtual g Production Energy loss patterns Direct Photon v2? v2 = azimuthal asymmetric production time Justin Frantz QNP’06 Madrid

  3. Greater Picture Pseudo-Cronological Progression of Direct Photon Theory/Studies/Measurements in HI A healthy and expanding sub-field ! BASIC IDEA: EM g provides clean/different view of QCD interactions/matter Soft Spectrum Hard Spectrum QGP/Hadron Thermal Rates/Info pQCD/Jet Suppression Control Intermediate pT Spect. Jet-medium g-h (jet) Rates Hadron v2 Control g-g HBT rates + spacial info g-jet Correlation Shapes Di-photons Forward Prod CGC Virtual g Production Energy loss patterns Direct Photon v2? v2 = azimuthal asymmetric production time Justin Frantz QNP’06 Madrid

  4. How does PHENIX map onto this? • Many Experimental Methods/Avenues: • Standard Statistical Method (Large Meson Decay Photon Background!) • p0 (Anti) Tagging Method • Cone Method • Isolation Cuts • e+e- Photon Conversion • Virtual Photons via Di-electrons* • Hard Photon-Jet Correlations • Combined w/ Reaction Measurements (v2) Justin Frantz QNP’06 Madrid

  5. Standard Statistical Method • Measure p0 and Inclusive g spectra • Generate expected gdecay from p0 (e.g.h mT scaling) w/ MC • Excess in Ratio g/gdecay is direct photon signal • Generally we take g/gd= g/ p0÷ gd/ p0 Justin Frantz QNP’06 Madrid

  6. w/ pQCD Denominator!!! RAA = sA+A /(TAA sp+p) Review: Au+Au Results • High pT signal clear since meson production suppressed at RHIC—consistent with thickness scaling of pQCD g PHENIX nucl-ex/0503003 200 GeV Red Curve: pQCD w/ decay photon suppresion Justin Frantz QNP’06 Madrid

  7. New! New! New! New Au+Au Results • New Run4 data (including brand new points) • Kink persists…hmmm…(jet-medium?) Au+Au 200 GeV Run4 Dataset Red PbGl Black PbSc Justin Frantz QNP’06 Madrid

  8. hep-ex/0501066 Review: p0 Tagging Methods p+p • Improves signal to bkg @ low pT • Start with Anti-tagged sample (p0 rec. not possible) • Correct for fake non-tags with input p0 spectrum* • Rtag = fraction of tagged to non-tagged • Current p+p/d+A results: new p+p publication soon (~ 1 month?), goes slightly lower in pT • p+p/d+Au consistent also w/ pQCD but with large systematics still @ low pT Justin Frantz QNP’06 Madrid

  9. ~ Direct g Recent d+Au Re-analysis • Peressounko Hard Probes talk in 1 wk. Fill in low pT • Several signif. error sources better understood • Energy scale difference Gl. vs. Sc. better understood • Less p0 Acceptance sensitivity • Using “Cone angle q method” • Instead of measuring one fixed Rtag, fit Rtag angular dependence • Rtagq dependence known • Non-tag→“constant background” • In future improve Au+Au/other system systematics in same way… Next Week! Hard Probes ‘06 Preliminary d+Au “Anit-Tagged Ratio” (q) “Re-scaled” Cone Size q Justin Frantz QNP’06 Madrid

  10. JETPHOX =pT BFG set2, CTEQ6M Vogelsang, W. Iso cone R=0.4 =pT, CTEQ6M Isolation Cuts and Fragmentation g • Traditional isolation cut analysis for hard scattering in p+p also increases S/B but (/and?) biases physics process (removes Bremstrahlung/Frag) • Isolation cut: 0.1*E > Econe(Riso=0.5rad) • NLO Calc w/ 30-40% Brems. @ high pT consistent w/ data (PHENIX iso. cut catches ~ 20%) p+p 200 GeV p+p 200 GeV Ratio Justin Frantz QNP’06 Madrid

  11. g RAA & Considerations • Real RAA better than comparisons w/ pQCD in HI • (note: Run2 data) • Fragmentation g in HI should be suppressed • Nominally, believed RAA should be < 1 (although see Zakarov hep-ph/0405101) • Also, recent paper (Arleo et.al.) • Isospin considerations p+p != A+A • shadowing at higher pT • Data consistent with reduction from any of above effects RAA = AA/(scaled pp) Real RAA PHENIX 200 GeV hep-ph/0601075 Justin Frantz QNP’06 Madrid

  12. New Methods for Softer Photons • Optimized Run4 Analysis at low pT • Extreme stability cuts • Optimized “Principal Component”-like photon PID cuts • Signal level consistent w/ Run2 results • Slightly higher Au+Au 200 GeV Justin Frantz QNP’06 Madrid

  13. Photon Conversion Method • Mis-rec’d momentum→non-zero conversion pair mass • Purity cut uses opening angle orientation w.r.t. magnetic field • Electron systematics same or smaller than EMCal • Bkg. Normalization easier (di-electron ~< 1% syst.) • Better Mom resolution @ low pT • Abs. efficiency difficult • Independent measurement (error reduction) • Excess ratio: Work in Progress presented 2 wks ago @ HotQ.06 • Result by Nov. (QM’06) expected Purity cut PHENIX Beam Pipe r Run4 data r = mass vs f Justin Frantz QNP’06 Madrid

  14. e+ e- g* q g q 90-140 200-300 90-300 MeV 140-200 MeV ÷ ÷ Virtual Direct Photons All sources of real g also produces virtual internal conversion g* Knoll-Wada Formula for Internal Conversion g* Look at “high” pT ( > 1.5 GeV/c) e+e- pairs Direct g in green negligible Any relative excess in brown from Knoll Wada p+hratios is ~direct photons 0-30 Di-electron Mass Spectrum Rdata ÷ Justin Frantz QNP’06 Madrid

  15. Virtual Direct Photons • Results robust w/ different mass regions • Positive signal clear • Consistent with other methods • Knoll-Wada assumption for virtual photons? • Necessary to integrate excess over all mass→total inclusive g* • Coherent charge effects? • Longitudinal polarization states for virtual g in the medium? • “Model dependence?” Try other di-lepton prediction “models”? Justin Frantz QNP’06 Madrid

  16. Gamma-Jet Correlations • 2-particle correlation method at RHIC: • Plot correlation C(Df) of particle pairs vs. azi-opening angle Df • Di-jet production causes large correlated production at 0 (nearside) and p (awayside) • LO g-jet w/ causes nearside “disappearance” for g triggers g-jet jet-jet pairs = “triggers” w/ pTtrig C(Df) x “associated’s” w/ pTa p p 0 0 p0-h g-h Observed in PHENIX by comparing p0-h and inclusive g-h (including decay g) Increasing direct g Justin Frantz QNP’06 Madrid

  17. Gamma-Jet Information • How to take these correlation functions → energy loss? • QM’05 & DNP 10/05 • Integrate jet-correlated yields on awayside • xE ~= pTa normalized by trigger pTtrig • Slope of “exponential” distribution senstive to energy loss • Change in slope vs centrality due to direct g or decay g kinematic effects? (inclusive p0 spectrum changes with centrality) Justin Frantz QNP’06 Madrid

  18. Jet-medium g? f-fR Direct Photon v2 • Measure the Reaction Plane fR • Particle production at (f – fR) → v2 • Indications of direct photon in inclusive (decay + direct) g flow? • Repeat direct g Stat. Method vs. fR • p0 suppression vs should make signal visible for some • Jet-medium interactions: reflecting suppression vs. v2 these g also have v2 (but negative – see hep-ph/0508201) • Higher statistics Run4 work in progress result shown in Spring JPS 06 PHENIX Preliminary PHENIX p0 RAA nucl-ex/0508019 f-fR Justin Frantz QNP’06 Madrid

  19. Summary • Progress made on many fronts • Many methods in PHENIX exploring many questions in nicely developing sub-field • Statistical Methods in Au+Au measure novel reduction in background • Sig/Bkg boosting methods employed in p+p/d+Au • Systematic error improvements in near future! • Photon Conversions via di-electrons entirely different method/ same measurement • Virtual g via di-electrons at very low mass new idea shows interesting signal • g-jet studies underway, in progress to yield interesting geometrical information • Direct g flow studies underway for same/ testing jet-medium predictions Justin Frantz QNP’06 Madrid

  20. Outline • Hard and Soft Direct Photon Probes • Ingredients: • New d+Au, old p+p, old p+p brems. Baselines , RdA for direct photons? • Discuss N+N not p+p • Run 4 Au+Au direct photon RAA/ratio’s High pT, low pT • Dielectron results intro • Yasayuki’s direct photon, other soft methods • Compare soft regions measurements/compare to theory? • Gamma-jet: xE: pi0 xE Justin Frantz QNP’06 Madrid

  21. Jet-Photon Conversion (Jet-Plasma Interaction) • Multiple Scattering: • Not important for parton Eloss (?) • But large addition to small gdirect • Kinematics: small u dominates: pg ≈ pq • Model jets traversing q/g bath • First Order Calc Fries, et. al. • Fq(p) ~ Static Thermal • More complete treatment Turbide,Gale et. al. • Fq(p) evolution using AMY formalism • Question: aS modified in medium LO Cross Sections Justin Frantz QNP’06 Madrid

  22. Photon-Jet Correlations • Motivation: Direct Photon (e.g. Energy) Cleanliness: high pT • Convenient for triggering • Subtract p0 decay photon trigger distribution - use charge pions • Azimuthal correlations: separate (jet-medium) Brems and Compton direct on the near side: M.Chiu Au+Au QM’02 d+Au p0/Brems Compton g Justin Frantz QNP’06 Madrid

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