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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 Norbert Novitzky, Jiri Kral Sami Räsänen, Jan Rak Jyväskylä University & Helsinki Institute of Physics, Finland. 3rd Nordic "LHC and Beyond" Workshop, Lund. Outline of the talk. Open Questions from RHIC

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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 Norbert Novitzky, Jiri Kral Sami Räsänen, Jan RakJyväskylä University & Helsinki Institute of Physics, Finland 3rd Nordic "LHC and Beyond" Workshop, Lund DongJo Kim, LHC and Beyond 2009

  2. Outline of the talk • Open Questions from RHIC • RAA, IAA • Modification of the Fragmentation in AA • Two particle correlation • Kinematics • What we have learned from di-hadron correlation ? • What we can obtain from gamma-hadron correlation ? • Gamma-Hadron Correlation Result in p+p ( PHENIX ) • Still various Contributions to be Understood ? • Soft QCD radiations • Quark Fragmentation only ? • -jet momentum imbalance due to the kT smearing (Details in Sami Räsänen’s Talk) • Conclusion and Open Issues DongJo Kim, LHC and Beyond 2009

  3. 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, LHC and Beyond 2009

  4. leading particle - trigger pTt away-side fragments - associated particles pTa 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) DELPHI, Eur. Phys. J. C13,543, (1996) OPAL Z.Phys. C 69, 543 (1996) • Assumption: • Leading particle fixes the energy scale of the trigger & assoc. jet • => DongJo Kim, LHC and Beyond 2009

  5. 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, LHC and Beyond 2009

  6. Two-particle correlations in p+p Fragmentation function D(z) and Intrinsic momentum kT • 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) . 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, LHC and Beyond 2009

  7. 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, LHC and Beyond 2009

  8. Trigger associated spectra are insensitive to D(z) yield bq=8.2 – Quark FF --- Gluon FF LEP data bg=11.4 Phys.Rev.D74:072002,2006 – DELPHI, Eur. Phys. J. C13,543, (1996) --- OPAL Z.Phys. C 69, 543 (1996) DongJo Kim, LHC and Beyond 2009

  9. 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, LHC and Beyond 2009

  10. π0-h xE distribution from PYTHIA PYTHIA • Even with higher xE region Slope gets larger as you go higher pt • PYTHIA fit : 0.2<xE<0.8 • Unknown quark/gluon contributions increase the systematic higher DongJo Kim, LHC and Beyond 2009

  11. 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, LHC and Beyond 2009

  12. What about LHC ? PHENIX measured pTpair=3.360.090.43GeV/c extrapolation to LHC k2T ~ 6.1 GeV/c DongJo Kim, LHC and Beyond 2009

  13. 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 PYTHIA D(zt) (zt) DongJo Kim, LHC and Beyond 2009

  14. 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, LHC and Beyond 2009

  15. PHENIX s=200 GeV 0 and dir- assoc. distributions Run 5+6 p+p @ 200 GeV Isolated photons DongJo Kim, LHC and Beyond 2009

  16. 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, LHC and Beyond 2009

  17. 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, LHC and Beyond 2009

  18. xE distribution comparisons (-h) quark vs gluon in KKP (2)’ PYTHIA (2) (1) • PHENIX xE distributions and local slopes are compared with PYTHIA and KKP • PHENIX fitting ranges are limited by statistics • Local slopes are getting steeper as Trigger pT gets higher • (1) pT,trigger > ~ 15 , PYTHIA were fitted with fixed range ,0.1<xE<0.3] • (2)(2)' KKP is much steeper in low xE than PYTHIA Nucl. Phys., 2001, B597, 337-369 Parameters a, b and g from PRD74 (2006) 072002 DongJo Kim, LHC and Beyond 2009

  19. Local slopes In Various xE ranges • 0.2<xE<0.4 (2) 0.2<xE<0.8 (3) 0.4<xE<0.8 PYTHIA -u quark jet (Compton) 66 % -gluon jet (Annihilation) 17 % • Deviation at low pT due to the kT bias. • Unlike the di-hadron correlation it asymptotically converges to the correct value ~exp (-6.2z ) in higher xE region DongJo Kim, LHC and Beyond 2009

  20. Need to go higher trigger and xE D(z) ~ exp(-6z) Sami Räsänen’s Talk (afternoon) kT smearing effect D(z) ~ z-a(1-z)b(1+z)-g Parameters a, b and g from PRD74 (2006) 072002 DongJo Kim, LHC and Beyond 2009

  21. PHENIX dir- assoc. distributions measures FF quark vs gluon in KKP (2)’ Run 5+6 p+p @ 200 GeV Isolated photons PHENIX xE Bin (2) 0.4<xE<0.8 (1) • PHENIX measures FF in low xE or low <z> ? • PYTHIA and KKP shows the similar trend as data in 5<pTt< 15 GeV • KKP steeper than PYTHIA in low xE region • as xE gets higher, KKP ~ PYTHIA • Finalizing the data and go to higher xE ( pi0 in associated bin ) DongJo Kim, LHC and Beyond 2009

  22. 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 • 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. • PHENIX measured the xE distribution associated with isolated photon • is consistent with KKP, only accessible in low xE or <z> region. • PYTHIA agrees with Initial/final state radiation on. • Need to go higher xE (ala . Pi0 as associated particle ) • kT-bias still present - pushes the minimum photon-trigger pT above 10 GeV/c at RHIC and 30 GeV/c at LHC : Sami’s talk. DongJo Kim, LHC and Beyond 2009

  23. LHC 14TeV PYTHIA -gluon jet (Annihilation) 17 % -u quark jet (Compton) 66 % NLO :hep-ph/9910252 points are p+p 14 TeV PYTHIA xE distribution, dashed line KKP FF parameterization Nucl. Phys., 2001, B597, 337-369 DongJo Kim, LHC and Beyond 2009

  24. 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, LHC and Beyond 2009

  25. 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, LHC and Beyond 2009

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