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Analysis of the Direct photon associated spectra from RHIC to LHC

Analysis of the Direct photon associated spectra from RHIC to LHC. DongJo Kim Rafael Diaz, Norbert Novitzky, Tuomo Kalliokoski Timo Alho, Sami Räsänen, Jan Rak Jyväskylä University & Helsinki Institute of Physics, Finland. High-pT Physics at LHC, Tokaj'08. Outline of the talk.

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Analysis of the Direct photon associated spectra from RHIC to LHC

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  1. Analysis of the Direct photon associated spectra from RHIC to LHC DongJo Kim Rafael Diaz, Norbert Novitzky, Tuomo Kalliokoski Timo Alho, Sami Räsänen, Jan RakJyväskylä University & Helsinki Institute of Physics, Finland High-pT Physics at LHC, Tokaj'08 DongJo Kim, Tokaj 2008

  2. Outline of the talk • Open Questions from RHIC • RAA • Modification of the Fragmentation in AA • Two particle correlation • Kinematics • What we learned from di-hadron correlation ? • What we can obtain from gamma-hadron correlation? • Gamma-Hadron Correlation • Still various Contributions to be Understood ? • Soft QCD radiations • -jet momentum imbalance due to the kT smearing • Conclusion and Open Issues DongJo Kim, Tokaj 2008

  3. On the mission from RHIC to LHC • Great success of RHIC gave us a • perfect liquid • sQGP • test bench for string theory (AdS/CFT) • but also an opportunity to ask why: • Light and heavyquarks suppression looks so similar: • Quarks and gluons suppression looks similar: • Direct photon suppression at high pT looks similar: • Two particle correlations - more detailed view into a nature of parton interactions with QCD medium. Access to parton intrinsic momentum kT -> soft pQCD radiation, jet shape parameters jT -> induced radiation, fragmentation function -> energy loss. • Di-hadron correlations and conditional yields • Direct photons-hadron correlations in p+p @ s=200 GeV and 14 TeV DongJo Kim, Tokaj 2008

  4. PHENIX Charm , PRL. 98, 172301 (2007) Nuclear Modification Factor for various particles PHENIX Medium tomography: T. Renk, K. Eskola hep-ph/0610059 M. G. Mustafa, Phys.Rev.C72:014905,2005

  5. More intuitive exercises…. Single Di-hadron • can’t get error on best fit from 2/d.o.f curves, need 2. N standard deviation errors on fit parameters are given by 2= 2min + N2, so depending on d.o.f can’t really tell from 2/d.o.f whether IAA gives better constraint than RAA • However 2min/d.o.f=2.8 for IAA fit seems too large to be acceptable. (?) y (fm) c2 (IAA) x (fm) c2(RAA) • IAA better than RAA at RHIC and LHC • RAA similar situation between RHIC and LHC • IAA looks better probe in LHC Zhang,Owens,Wang, PRL 98 212301 (2007) NLO pQCD + KKP FF + expanding medium T.Renk, K.Eskola, PRC 75, 054910 (2007) DongJo Kim, Tokaj 2008

  6. 6< pT trig < 10 GeV STAR Preliminary IAA is better than RAAGamma-h will be better (1) (2) (3) (2) • Inconsistent with Parton Quenching Model calculation • (1) C. Loizides, Eur. Phys. J. C 49, 339-345 (2007) • Modified fragmentation model better • (2) H. Zhang, J.F. Owens, E. Wang, X.N. Wang –Phys. Rev. Lett. 98: 212301 (2007) • Di-Hadron correlation is more sensitive for jet tomography than RAA (2)(3) • Gamma-h will be better but current results with very wide bins , not much different at this moment • (3) K.Eskola, T.Renk ,Phys.Rev.C75:054910,2007 Phys.Rev.C75:054910,2007 DongJo Kim, Tokaj 2008

  7. pThadron~2 GeV for Ejet=100 GeV pp-data also interesting =ln(EJet/phadron) 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 More Exclusive observ. - modification of D(z) Wang, X.N., Nucl. Phys. A, 702 (1) 2002 DongJo Kim, Tokaj 2008

  8. away-side fragments - associated particles pTa leading particle - trigger pTt is the jet fragmentation variable: zt and za pout kT xEz is a simplified Fragmentation Function, b~ 8-11 at RHIC How can one measure D(z) • Assumption: • Leading particle fixes the energy scale of the trigger & assoc. jet • => DongJo Kim, Tokaj 2008

  9. Phys.Rev.D74:072002,2006 N  A p + p  jet + jet Azimuthal correlation function in p+p @ s=200 GeV d+Au N jTjet fragmentation transverse momentum F  kTparton transverse momentum YA  folding ofD(z) and final state parton dist. DongJo Kim, Tokaj 2008

  10. Two-particle correlations in p+p Fragmentation function D(z) and Intrinsic momentum kT DongJo Kim, Tokaj 2008

  11. Correl. fcn width - kT and acoplanarity Lorentz boost => pT,pair || kT,t || kT,a colinearity Lab frame Hard scattering rest frame hadronic partonic DongJo Kim, Tokaj 2008

  12. Trigger associated spectra are insensitive to D(z) yield bq=8.2 – Quark FF --- Gluon FF LEP data bg=11.4 – DELPHI, Eur. Phys. J. C13,543, (1996) --- OPAL Z.Phys. C 69, 543 (1996) DongJo Kim, Tokaj 2008

  13. z-bias; steeply falling/rising D(z) & PDF(1/z) Fixed trigger particle momentum does notfix the jet energy! ztrig Varying pTassocwith pTtriggerkept fixed leads to variation of both trigger and associated jet energies. zassoc Angelis et al (CCOR): Nucl.Phys. B209 (1982) Unavoidable z-bias in di-hadron correlations DongJo Kim, Tokaj 2008

  14. k2T and zt 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 kT broadening - collisional energy loss. Direct width comparison is biased. Still, we would like to extract FF from our own data -> direct photon-h correl. DongJo Kim, Tokaj 2008

  15. h-h: Leading particle does not fix Energy scale. away-side fragments - associated particles pTa leading particle - trigger pTt pout kT xEz -h: direct gamma does fix Energy scale if no kT away-side fragments - associated particles pTa Direct gamma - trigger pTt pout kT xEz D(z) from gamma tagged correlation D(zt) (zt) DongJo Kim, Tokaj 2008

  16. Soft QCD radiation Hard NLO radiation Soft + hard QCD radiation kT phenomenology Back-to-back balanced Compton photo-production DongJo Kim, Tokaj 2008

  17. FF slope PHENIX s=200 GeV 0 and dir- assoc. distributions p0 Direct g Exponential slopes still vary with trigger  pT. If dN/dxEdN/dz then the local slope should be pT independent. Arbitrary Normalization Arbitrary Normalization Run 5 p+p @ 200 GeV Statistical Subtraction Method DongJo Kim, Tokaj 2008

  18. PYTHIA -h simulations at RHIC 1) Initial State Radiation/Final State Radiation OFF,<kT>2=0 GeV/c xE slope is constant 2) IR/FR ON, <kT>2= 3 GeV/c xE slope is raising! Also PYTHIA shows the same trend, though, not as large as in the data, not so trivial even with Direct photons 1) 2) DongJo Kim, Tokaj 2008

  19. Initial/Fina state radiation ON, k2T=5 GeV/c Pythia Initial/Final st. radiation & kT 1) Initial State Radiation/Final State Radiation OFF,<kT>2=0 GeV/c xE slope is constant 2) IR/FR ON, <kT>2= 5 GeV/c xE slope is raising! Also PYTHIA shows the same trend, though, not as large as in the data, not so trivial even with Direct photons Initial/Fina state radiation OFF, k2T=0 GeV/c DongJo Kim, Tokaj 2008

  20.  PYTHIA -h simulation pT,pair-  correlation 1) IR/FR kT ON 2) IR Only • 1) IR/FR kT ON • -h:pT,pair correlated with trigger photon • jet balance destroyed by kT. • h-h: jet balance destroyed by kTandzT • 2) IR Only • Not in the case of “Initial State Radiation”. • It is due to the collinearity of initial quark with photon DongJo Kim, Tokaj 2008

  21. -h correlation and kT bias • Question: • Can one extract the Fragmentation Function from -h associated distribution despite the kT bias? Solve for net-pair momentum DongJo Kim, Tokaj 2008

  22. -h correlation and kT bias And assuming 2D Gaussian distribution for pT,pair => A conditional probability for detecting photon pTt and assoc pTa given parton momentum pT in CMS of hard scattering as: DongJo Kim, Tokaj 2008

  23. -mometum distribution due to the kT smearing Lorentz Invariant Gaussian kT smearing -> non-Gaussian distributions even at high-pT. Good agreement between simul. And formulae. DongJo Kim, Tokaj 2008

  24. What about LHC ? PHENIX measured pTpair=3.360.090.43GeV/c extrapolation to LHC k2T ~ 6.1 GeV/c DongJo Kim, Tokaj 2008

  25. Folding with a Fragmentation function Assoc xE distrib for various slopes of D(z)exp(-k*z) • Deviation from dashed lines (the true slopes of D(z)) at low pT due to the kT bias. • Unlike the di-hadron correlation it asymptotically converges to the correct value. • Knowing that we could unfold the kT or correct for the bias. DongJo Kim, Tokaj 2008

  26. Comparisons to Pythia and PHENIX -h Pythia DongJo Kim, Tokaj 2008

  27. Comparison to KKP PYTHIA -gluon jet (Annihilation) 17 % -u quark jet (Compton) 66 % points are p+p 14 TeV PYTHIA xE distribution, dashed line KKP FF parameterization Nucl. Phys., 2001, B597, 337-369 DongJo Kim, Tokaj 2008

  28. Summary and Open issues • Inclusive and two-particle correlation measurement in the high-pT sector at RHIC opened a new window into a QGP physics. LHC will be an ideal laboratory - larger xsection and center-of-mass energy available for hard-probes production. • As a next goal after “day one” physics: di-hadron and direct photon-h correlations - base line measurement for nuclear modification study: • kT and initial/final state QCD radiation, resummation vs NLO • jT near-side jet shape modifications • fragmentation function - can be measured using jets - not from the first data. Despite our expectation FF is not accessible in di-hadron correlations. FF can be extracted from direct photons correlation only at relatively high trigger-photon momenta. • kT-bias still present - pushes the minimum photon-trigger pT above 10 GeV/c at RHIC and 30 GeV/c at LHC. • fragmentation photon contribution ? • We are at the beginning of hard-probes exploration in heavy ion environment - LHC (supported by RHIC) will be fun ! DongJo Kim, Tokaj 2008

  29. Direct photons won’t be easy at LHC Decay photons energy and asymmetry distributions are in the ideal situation (no detector response) flat. Below threshold hits 0 E E “Direct” photons from 0 Ecut/E  2% @ E =10 GeV, however, / ratio is also of that order -> Subtraction method we started recently the full PHOS simulation project -> DongJo Kim, Tokaj 2008

  30. PID FF studies MLLA + LPHD Sapeta, Wiedeman hep-ph/0707.3494 DongJo Kim, Tokaj 2008

  31. xE slopes DongJo Kim, Tokaj 2008

  32. Hard Process: Uncertainty from FF Wide z distribution • Wide z range • Due to interplay of steep jet pT distribution and steep fragmentation function. • z = 0.1 – 0.8 • Missing knowledge of gluon fragmentation at larger z. • Measurement from LEPII is not still enough for larger z. • 3 jets events or global analysis. • NLO FF parameters fit failed to describe the entire kinematic range (= scale violation) EPJC37(2004)25 DongJo Kim, Tokaj 2008

  33. Model Highlight DongJo Kim, Tokaj 2008

  34. h-h correlations - jet functions Cone angle (radians) unchanged near-side peak in the final jet functions when moving away from Reaction plane. Away side is clearly modified. pT (GeV/c) DongJo Kim, Tokaj 2008

  35. Assoc. yield - “Averaged” LO approach Assumption (Phys.Rev.D74:072002,2006 for details) : Invariant mass of mass-less partons in hard scattering CMS and in LAB is the same -> non-Gaussian kT-smearing. DongJo Kim, Tokaj 2008

  36. Final state parton dist and FF from data of pQCD? Effective FS parton distribution: 0 invariant cross section provides a constrain: Effective Fragmentation function: DongJo Kim, Tokaj 2008

  37. kT effect • Intrinsic : Fermi motion of the confined partons inside the proton. • NLO : Hard gluon radiation • Soft : Initial and Final state radiation, resummation techniques (hep-ph/9808467) Outgoing partons carries transverse momentum kT. • momentum imbalance (partons pt are not equal ) due to kTxcomponent • acoplanarity (the transverse momentum of one jet doesn’t lie in the plane determined by the transverse momentum of the second jet and the beam axes) due to kTycomponent . R. P. Feynman, R. D Field, and G. C. Fox, Phys Rev D18 1978 J. Rak and M. Tannenbaum hep-ex/0605039 v1 DongJo Kim, Tokaj 2008

  38. Direct Photon is isolated in p+p PHENIX PRL 98 (2007) 012002 pp @ √s = 200GeV pp @ √s = 200GeV QM08 PHENIX • Seems to imply Nfrag ≈ 66% of Ndir • Only from -0.5 - 0.5 • (Only ~50% of inclusive photons included ) • Which gives you “ Nfrag ≈ 33% of Ndir “ DongJo Kim, Tokaj 2008

  39. Fragmentation photons are isolated ? • pp @ √s = 14 TeV Pythia Gustavo Conesa Balbastre • Isolation done on the pure PYTHIA particles • || < 0.7, R=0.4, pTth = 1 GeV/c • Isolation Cut efficiency for direct and frag photons DongJo Kim, Tokaj 2008

  40. Baryon & meson NMF STAR Preliminary Quark, Gluon Energy Loss QM08 Mark Thomas Heinz Sapeta, Wiedeman hep-ph/0707.3494 DongJo Kim, Tokaj 2008

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