1. 11-Jun-15Jan Rak1 Jet properties from the conditional yields associated with high-p T  0 and direct photon Jan Rak Jyvaskyla University & HIP, Finland for the PHENIX collaboration Jan Rak Jyvaskyla University & HIP, Finland for the PHENIX collaboration

2. 11-Jun-15Jan Rak2 Why to study direct photon correlation Inclusive distributions - R AA - limited sensitivity to details of parton interaction with QGP –Energy loss, surface bias - different models similarity –  vs p R AA quark vs gluon R AA similarity –  vs direct gamma R AA similarity –Light vs heavy quark R AA (non-photonic electron) similarity Two particle correlations - more detailed view into a nature of parton interactions with QCD medium. Access to parton intrinsic momentum k T -> soft pQCD radiation, jet shape parameters j T -> induced radiation, fragmentation function -> energy loss. –Di-hadron correlations and conditional yields –Direct photons-hadron correlations in p+ p @  s=200 GeV

3. 11-Jun-15Jan Rak3 R AA sensitivity to P(  E,E)? T. Renk, k. Eskola et al. R AA sensitivity to P(  E,E)? T. Renk, k. Eskola et al. R AA uniquely determined by The E-loss probability can be defined: Where hard vertices and 2D hydro

4. 11-Jun-15Jan Rak4 R AA sensitivity - surface bias Singles: Dihadron: Medium tomography: T. Renk, K. Eskola hep-ph/0610059 What do we learn from R AA about the mechanism of quark and gluon interaction with QGP ? MJT comment: “Theory is interesting only if it doesn’t agree with the data.”

5. 11-Jun-15Jan Rak5 pions versus protons pions versus protons STAR : PRL 97, 152301 (2006) Question raised by STAR at QM06: shouldn’t be p and π supp. differently due to C A /C F ?

6. 11-Jun-15Jan Rak6 Question: high-p T photons At high-p T direct-  almost as suppressed as  0. Is it shadowing? Is the the quark  jet suppression? (Taadaki Isobe, QM06) Eskola et al. NPA696 (2001) 729 gluons in Pb / gluons in p x Anti Shadowing 30% contribution from jet frag.

7. 11-Jun-15Jan Rak7 pQCD quenching - modification of D(z) Wang, X.N., Nucl. Phys. A, 702 (1) 2002  = ln( E Jet / p hadron ) p T hadron ~2 GeV for E jet =100 GeV Borghini and Wiedemann, hep-ph/0506218 MLLA: parton splitting+coherence  angle-ordered parton cascade. Theoretically controlled, experimentally verified approach Medium effects introduced at parton splitting

8. 11-Jun-15Jan Rak8 Azimuthal correlation function in p+p @  s=200 GeV d+Au Phys.Rev.D74:072002,2006 NN AA  N   j T  jet fragmentation transverse momentum  F   k T  parton transverse momentum Y A  folding of D(z) and final state PDF. p + p  jet + jet 

9. 11-Jun-15Jan Rak9 Correl. fcn width - k T and acoplanarity p T,pair Lorentz boost preserves partonic hadronic Jet momenta imbalance due to k T smearing Lab frame Hard scattering rest frame From an analysis of associated yield

10. 11-Jun-15Jan Rak10 Assoc. yield - “Averaged” pQCD approach Assumptions ( Phys.Rev.D74:072002,2006 for details) : 1.Invariant mass of mass-less partons in hard-scattering CMS and in LAB is the same -> non-Gaussian k T -smearing 2.Effective parton distribution function: 3.Effective Fragmentation function: , ,  to be extracted from fit to gamma-h or LEP One can then evaluate: 1.Inclusive  0 cross section 2.Trigger  0 associated dist.

11. 11-Jun-15Jan Rak11 Trigger associated spectra are insensitive to D(z) LEP data MJT Approximation - Incomplete Gamma function when assumed power law for final state PDF and exp for D(z) yield

12. 11-Jun-15Jan Rak12 Unavoidable z-bias in di-hadron correlations Varying p Tassoc with p Ttrigger kept fixed leads to variation of both trigger and associated jet energies. z-bias; steeply falling/rising D(z) & PDF(1/z)  z trig   z assoc  Fixed trigger particle momentum does not fix does not fix the jet energy!

13. 11-Jun-15Jan Rak13 k T bias Small k T (Gauss) and large p T power law less probable than Large k T (Gauss) and small p T power law Even at relatively high photon momentum (10 GeV/c)  -h pairs still not fully in power law pQCD regime.

14. 11-Jun-15Jan Rak14  k 2 T  and  z t  in p+p @ 200 GeV from  0 -h CF Phys.Rev.D74:072002,2006 For D(z) the LEP date were used. Main contribution to the systematic errors comes from unknown ratio gluon/quark jet => D(z) slope. Base line measurement for the k T broadening - collisional energy loss. Direct width comparison is biased. Still, we would like to extract FF from our own data -> direct photon-h correl.

15. 11-Jun-15Jan Rak15 Avoidable in Direct Photons Correlations Avoidable in Direct Photons Correlations q qg γ q q g γ ComptonAnnihilation q q q q g g g γ γ Bremsstrahlung Direct Photon Processes These two diagrams fix the jet energy scale Up to the k T effect ! Fragmentation photons measured using isolation cut analysis

16. 11-Jun-15Jan Rak16 00 Direct  PHENIX  s=200 GeV  0 and dir-  assoc. distributions Run 5 p+p @ 200 GeV Statistical Subtraction Method Arbitrary Normalization Matthew Nguyen APS Spring Meeting, April 15, 2007 Exponential slopes still vary with trigger  p T . If dN/dx E  dN/dz then the local slope should be p T  independent. FF slope

17. 11-Jun-15Jan Rak17 Photon associated yields - “averaged” pQCD FF  exp(-6z) FF  exp(-8z) k T bias still important, sensitivity to the D(z) shape as expected, the slope is also changing as in the data - parton imbalance.

18. 11-Jun-15Jan Rak18 Summary Inclusive and two-particle correlation measurement in the high-p T sector at RHIC opened a new window into a QGP physics. Inclusive measurements have limited discrimination power -> complementary multiparticle correlations are important. However, two-particle correlations are not bias- free either: di-hadron correlations: k T and initial/final state QCD radiation, resummation vs NLO j T near-side jet shape modifications z-bias washes out the sensitivity of the associated x E yield to the Fragmentation Function. direct photon-hadron correlations Fragmentation function can be extracted from the associated x E yield. However k T -bias still present - pushes the minimum photon-trigger p T above 10 GeV/c at RHIC.

20. 11-Jun-15Jan Rak20 Question: non-photonic e  Heavy quarks are expected to loose less energy than light quarks, but @ 6 GeV/c: charm quarks (e  ) equally suppressed as light quarks (  0 ) Radiative energy loss only fails to reproduce non-photonic e  R AA and/or v 2 nucl-ex/0611018 (Phys. Rev. Lett.) Fragmentation and dissociation of hadrons from heavy quarks inside the QGP 25 fm 1.6 fm 0.4 fm B D QGP extent Possible interpretation: I. Vitev (A.Adil, I.V., hep-ph/0611109)

21. 11-Jun-15Jan Rak21 Popular interpretation - elastic energy loss S. Wicks et al., nucl-th/0512076 Partonic Energy Loss Radiative 2  N processes. Final state QCD radiation as in vacuum (p+p coll) - enhanced by QCD medium. Elastic 2  2 LO processes Elastic  E models predict significant broadening of away-side correlation peak - not seen in the data. Also various models differ significantly in radiative/elastic fraction.

22. 11-Jun-15Jan Rak22 Jet quenching - one of the most celebrated results. Light mesons suppressed by factor of 5, direct-  unsuppressed => FS nature of observed suppression. Data successfully described by pQCD models. Measured for: variety of species  0,  , ,  dir, p, K S, , , J/ ,  … and CMS energies  s=17, 22.4, 62.4, 130, 200 GeV/c Density of scattering centers Range of color force Transp. Coef. Scatt. power of QCD med:

23. 11-Jun-15Jan Rak23 Inclusive nuclear suppression factor R AA is not quite sensitive to the particular dE/dx mechanism - is it due to the surface bias? Light and heavy quarks suppression looks similar: Quarks and gluons suppression looks similar: Direct photon suppression at high p T looks similar: Some of the open questions It is evident that the detailed understanding of unmodified parton properties CRUTIAL

24. 11-Jun-15Jan Rak24 Photons in PHENIX Two types of highly segmented EM calorimeters > 24K towers Photon and  0 measurements at very high p T Cross sections agree reasonably with NLO calculations 8.1/  E(GeV)  2.1 % 5.9/  E(GeV)  0.8 % PbSc PbGl Direct photon cross section in p+p

25. 11-Jun-15Jan Rak25 Direct  -h Correlations in PHENIX p+p  s=200 GeV Run 5 p+p @ 200 GeV 5-7 X 1-2 GeV/c 7-9 X 1-2 GeV/c 5-7 X 2-5 GeV/c 7-9 X 2-5 GeV/c 9-12 X 2-5 GeV/c 9-12 X 1-2 GeV/c Statistical Subtraction method:  direct =  all -  decay Matthew Nguyen APS Spring Meeting, April 15, 2007 Signature small near-side correlation signal apparent Yield sensitive to  contribution at the near-side Still room for some fragmentation contribution