1 / 35

High p T g -h Correlations Using the PHENIX Detector

High p T g -h Correlations Using the PHENIX Detector. Matthew Nguyen, Stony Brook University. Why Direct Photon Correlations?. “Leading Order” Picture Exact Momentum Balance w/ Away-Side Jet Compton Dominance p+p : Measure Gluon Distribution Function A+A:

gianna
Download Presentation

High p T g -h Correlations Using the PHENIX Detector

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. High pTg-h Correlations Using the PHENIX Detector Matthew Nguyen, Stony Brook University

  2. Why Direct Photon Correlations? • “Leading Order” Picture • Exact Momentum Balance w/ Away-Side Jet • Compton Dominance • p+p: Measure Gluon Distribution Function • A+A: • Calibrated Probe of Energy Loss • More Sensitive Probe than single particle spectra, Di-Hadron Correlations • The Golden Channel for Jet Tomography? • the fine print • Fragmentation photons • Initial state effects (Shadowing , kT) • Still sensitive to geometry / space-time evolution • Quark vs. Gluon Energy Loss q γ γ q g q g q Compton Annihilation Direct Photon Processes at LO X.N. Wang, Z. Huang PRC55 (1997) 3047-3061 IAA Quark Matter 2008

  3. g-h Correlations in PHENIX Drift Chamber Electromagnetic Calorimeters Direct photon cross section in p+p h-h Correlations in Au+Au PbGl PbSc Quark Matter 2008

  4. PYTHIA 6.1 Statistical Subtraction Method Photon Sources in PYTHIA • Large background from meson decay • Direct g S/B increased by jet suppression in central Au+Au collisions • p0-h decayed via MC to get decay g-h • h-h measured in p+p • Rg = Ng (inclusive) / Ng (decay) • Can perform a statistical subtraction of per-trigger yields: • Method well-suited for high multiplicity environment (Au+Au) Rg measurement in Au+Au 200 GeV Rg Where Y = # hadrons per photon pT [GeV] Quark Matter 2008

  5. QM2006 Direct Photon-Hadron Results At QM2006 PHENIX showed “proof of principle” level g-h results Run 5 p+p @ 200 GeV Run 4/5 p+p/Au+Au @ 200 GeV • Subtraction method is robust • Near-side disappearance consistent with g+jet expectations • Away-side comparable to hadron triggered case • Away-side yields in Au+Au are suppressed compared to p+p • g-h measurement is statistics limited Quark Matter 2008

  6. New Results  Increased Precision 1/Ntrig dN/dDf (A.U.) • Systematic error dominated by uncertainty in Rg and h-h contribution *Note: Run 6, 7 Absolute Efficiencies not finalized – In Arbitrary Units Quark Matter 2008

  7. Direct Photon-HadronDf Correlations in p+p pT,hadron 1/Ntrig dN/dDf (A.U.) Df [rad] pT, photon Subtraction technique works over wide range of pT! Quark Matter 2008

  8. Photon Recoil Jets Run 6 p+p @ 200 GeV Per-Trigger Yield (A.U.) h-h measurement pT, photon • 1st approximation -- g recoil jets similar to hadron triggered jets in p+p • <Q2> of hard scattering should be lower due to z bias in hadron-triggered correlations • kT effect need not be the same – needs to be measured • g triggered yields sensitive to the FF g-h measurement Quark Matter 2008

  9. Vacuum Fragmentation Function p+p @ 200 GeV PRD 74 (2006) 072002 • Baseline for modified FF in Au+Au • p0-h xE distributions were shown to poorly discriminate between quark (– ) and gluon(--) fragmentation due to p0 trigger bias (z<1) Run 5 Direct g-h Run 3 p0-h 1/Ntrig dN/dxE( A.U.) – Quark FF --Gluon FF Preliminary • In “leading order” picture: • Direct photon xE distributions • should be sensitive to underlying • (quark) fragmentation function • Use Run 6 data to reduce errors – DELPHI, Eur. Phys. J. C13,543, (1996) -- OPAL Z.Phys. C 69, 543 (1996) Quark Matter 2008

  10. Au+Au Run 7 Direct Photon-Hadron Correlations (7 < pT,g < 9) 0 Au+Au analysis is challenging: Additional sources of uncertainty from underlying event subtraction (ZYAM), elliptic flow subtraction and p0 combinatoric background Little or no near-side production associated with direct photon triggers Away-side yields indicate large jet suppression in g+jet channel Working to reduce systematics and more data to analyze (~2X) Quark Matter 2008

  11. The pT Landscape Direct Photon S/B (Rg) p0 Combinatoric S/B pQCD Accuracy pT,hadron Correlation Function(A.U.) Correlation Function(A.U.) Run7 Au+Au 200 GeV Run7 Au+Au 200 GeV 12-15 X 3-5 GeV 7-9 X 3-5 GeV Rate Jet S/B Near/Away-Side > 1 Near/Away-Side ≈ 1 pT, photon Quark Matter 2008

  12. Near-Side Fragmentation Run 6 p+p @ 200 GeV Per-Trigger Yield (A.U.) h-h measurement pT, photon 0.3 0.25 0.2 0.1 z • Near-Side yield small but non-zero • for z  0 • Expect near-side contribution from photon fragmentation • Systematic errors for g-h correlations • large on the near-side g-h (h-g) measurement Quark Matter 2008

  13. Fragmentation Photons q g γ • Fragmentation diagrams must be included at NLO to cancel divergences • |z| < 1 for fragmentation photons, but how much less? • Dparton/photon(z) not well constrained • May oppose either quark or gluon jets • Important for LHC • Suppressed by E-loss q γ q g g q Bremsstrahlung diagrams Induced Bremstrahlung I. Vitev, 2007 RHIC-AGS Meeting --RHIC – LHC Rate of fragmentation photons may be increased by presence of medium partons Quark Matter 2008

  14. h-g Correlations X10-3 • Idea: By triggering on a hadron and looking for near-side direct photon partners one can measure the fragmentation photon yield directly • Measure hadron - inclusive g and hadron - decay g correlations • Decay corr’s are made by tagging p0 and h by invariant mass • Must know tagging efficiency and false tagging rate precisely  dominant source of systematic uncertainty h-inclusive g X10-3 h-decay g X10-6 2.5 < pT,g < 3.5 10-6 h-direct g Quark Matter 2008

  15. h-g Correlations II • First measurement of it’s kind at RHIC! • Will measure jet shape distributions, e.g. xE, pout • Constrain photon FF? • Nfrag/Ninc ≈ 0.1 at intermediate pT • Measure in Au+Au Quark Matter 2008

  16. Outlook • Direct photon-hadron correlations are moving from the proof of principle stage towards the precision measurement stage • Finalizing Run 6 p+p for increased precision and broader kinematic range compared to previous results • Analyzing Run 7 Au+Au data set and working to reduce systematic uncertainties • Baseline measurements of g-h and h-g correlations are being made to ensure that theory is well under control • Fragmentation component measured – Nfrag ≈ 0.1 Ninc • Away-side jet suppression in the g+jet channel appear strong • PHENIX is currently working on Run 6 and Run 7 p+p and Au+Aug-h correlations at high pT Quark Matter 2008

  17. Backup Slides Quark Matter 2008

  18. Constructing the Decay Background • To start: Construct g(p0) - h from p0-h • Problem is that tagging the p0’s introduces a bias <pT> tagged = <pT> true • Developed a pair-by-pair correction procedure Correction Procedure: Per-Trigger Yield from g(p0): Sample MC weight function: • Decay kinematics reproduced by Monte Carlo include energy resolution effects and acceptance (P) • This is just for p0’s, What about contributions from other mesons?  This approach implicitly assumes they have the same associated yield – Analytic Form – w/ Detector Response Quark Matter 2008

  19. h-h Correlations Run 5 p+p @ 200 GeV • Parent-h • First measurement of h-h correlations at RHIC! • g(h)-h Yields generated by same procedure as g(p0)-h • Combinatorial background under h peak subtracted using a sideband procedure PRC 75, 024909 (2007) • h-h • g(h)-h Quark Matter 2008

  20. QGP Induced Photon Production Jet Conversion– Hard partons re-scatter off medium partons via Compton process Induced Bremsstrahlung – Rate of fragmentation photons increased by presence of medium partons Induced Bremstrahlung Jet Conversion • Both effects still speculative • Are there experimental signatures? • pT, v2 dependence (see other talks in session) • h-g correlations Zharkarov – JETP Lett. 80 (2004) Turbide et al., Phys. Rev. C72 (2005) Quark Matter 2008

  21. Prompt Photon Spectrum Quark Matter 2008

  22. p+p Integrated Yields Quark Matter 2008

  23. kT Effect kT Effect: Net momentum of di-jets (and g-jets) due to initial state radiation xE slopes for g-h from PYTHIA kT measurement for p0-h PRD 74 (2006) 072002 • kT = 2.5 GeV • kT = 0 PYTHIA shows that kT changes the xE distribution significantly kT measurement in g-h is needed kT measurements the di-jet channel show a large effect -- 2.5 – 3.0 GeV Quark Matter 2008

  24. Gluon Fragmentation Functions Inclusive production from AKK FF • Gluons contribute significantly to • single inclusive measurements at RHIC • However different parameterizations give divergent estimations of gluon contribution • e.g., AKK FF’s indicate much higher gluon contribution than previous fits Compilation by Hirai et al. Phys Rev D75 (2007) 94009 Quark Matter 2008

  25. Rg from Run 4 Au+Au 200 GeV Quark Matter 2008

  26. Using p+p data in FF‘s De Florian, Sassot, Stratmann STAR, Phys Lett B, 637 (2006) 161 hep-ph:0707.1506 Phys. Rev. D75, 114010 (2007). STAR identified hadron spectra constrain the gluon FF at large z Use twoparticle correlations to constrain g p at all z? New set of fragmentation functions include p+p (and DIS) data and obtain very different parameterizations of the gluon FF’s Quark Matter 2008

  27. γ q g q Identified Hadron Correlations • g recoil jets more likely to be a quark jet than p0 recoil jets • Quark and gluon jets may have different particle content •  p/p on the away-side of g vs. p0 recoil sensitive the FF’s For definiteness assume: In this simplified picture particle ratios can be written in terms of FF’s: & Kretzer Acta Phys. Polon. B36, 179 (2005) Quark Well constrained from e+e- Quark/Gluon Contribution Double ratio gives partial cancellation of systematics due to particle identification and direct photon subtraction Gluon pT(p) Quark Matter 2008

  28. g-Identified h Results (Under Construction) g- identified hadron correlations can be performed in the range 5 < pTg < 12 X 1 < pTh <2 This corresponds to about 0.1 < z < 0.2 5 < pTg < 7 X 1 < pTh < 2 PHENIX Arbitrary Normalization • Hadron efficiencies not finalized • Systematic errors are large but • will most cancel in ratio • So far run 5 only • Run 5 + 6 should enable a significant • measurement (integrated over away-side) Quark Matter 2008

  29. Rg from p+p Collisions In p+p there is no published Rg but deriveable from p0 and g spectra For pure power law: N(p0)/N(g) = (n-1)/2; n = p0 slope parameter Quoted from g x-sec analysis Quark Matter 2008

  30. Trigger Biases and the kT effect • Insensitivity of dN/dxE to true FF is the interplay of two trigger biases: • Trigger Bias #1: Trigger requirement • biases the near side FF to high z • Does not affect away-side jet • Absent in g-h kT Effect: Acoplanarity of di-jets (and g-jets) due to initial state radiation • Trigger Bias #2: Longitudinal • component of kT biases jet CM in • direction of the trigger for pT,t > pT,a • Does affect the away-side jet • Present in g-h kT effect affects: • away-side jet width • Inclusive high pT x-sections • Recoil spectra (dN/dxE) kT described by NLO, Why do we need to measure it? kT measurement for di-jets Quark Matter 2008

  31. Gluon Fragmentation The gluon fragmentation function has large uncertainties! Is there an independent test of gp? Quark Matter 2008

  32. Data Fit pQCD Limitations Auranche 2006 Closer: Agreement only 20% Not good enough to constrain kT Agreement w/ data is remarkable! Better than jet cross-sections Quark Matter 2008

  33. kT in the g-jet channel M. Begel, Nucl. Phys. B 79, 244 1999; Ph.d thesis (1998) Independent of process Measurement for g-p0 at lower Quark Matter 2008

  34. Quark Matter 2008

  35. Quark Matter 2008

More Related