1. 2/3/090 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 DongJo Kim, LHC and Beyond 2009

2. Outline of the talk 1)Open Questions from RHIC a)R AA, I AA b)Modification of the Fragmentation in AA 2)Two particle correlation a)Kinematics b)What we have learned from di-hadron correlation ? c)What we can obtain from gamma-hadron correlation ? 3)Gamma-Hadron Correlation Result in p+p ( PHENIX ) –Still various Contributions to be Understood ? a)Soft QCD radiations b)Quark Fragmentation only ? c)  -jet momentum imbalance due to the k T smearing (Details in Sami Räsänen’s Talk) 4)Conclusion and Open Issues 2/3/091DongJo Kim, LHC and Beyond 2009

3. 2/3/092 More Exclusive observ. - 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 pp-data also interesting DongJo Kim, LHC and Beyond 2009

4. 2/3/093 How can one measure D(z) Assumption: Leading particle fixes the energy scale of the trigger & assoc. jet => leading particle - trigger p Tt xEzxEz p out kTkT away-side fragments - associated particles p Ta is the jet fragmentation variable: z t and z a is a simplified Fragmentation Function, b~ 8-11 at RHIC DongJo Kim, LHC and Beyond 2009 DELPHI, Eur. Phys. J. C13,543, (1996) OPAL Z.Phys. C 69, 543 (1996)

5. 2/3/094 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 parton dist. p + p  jet + jet  DongJo Kim, LHC and Beyond 2009

6. 2/3/095 Two-particle correlations in p+p Fragmentation function D(z) and Intrinsic momentum k T Fragmentation function D(z) and Intrinsic momentum k T DongJo Kim, LHC and Beyond 2009 R. P. Feynman, R. D Field, and G. C. Fox, Phys Rev D18 1978 J. Rak and M. Tannenbaum hep-ex/0605039 v1 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).

7. 2/3/096 Correl. fcn width - k T and acoplanarity Lorentz boost => p T,pair || k T,t || k T,a colinearity partonic hadronic Lab frame Hard scattering rest frame DongJo Kim, LHC and Beyond 2009

8. 2/3/097 LEP data yield Trigger associated spectra are insensitive to D(z) b q =8.2 b g =11.4 DongJo Kim, LHC and Beyond 2009 – Quark FF --- Gluon FF – DELPHI, Eur. Phys. J. C13,543, (1996) --- OPAL Z.Phys. C 69, 543 (1996) Phys.Rev.D74:072002,2006

9. 2/3/098 Unavoidable z-bias in di-hadron correlations z-bias; steeply falling/rising D(z) & PDF(1/z)  z trig   z assoc  Varying p Tassoc with p Ttrigger kept fixed leads to variation of both trigger and associated jet energies. Fixed trigger particle momentum does not fix does not fix the jet energy! Angelis et al (CCOR): Nucl.Phys. B209 (1982) Angelis et al (CCOR): Nucl.Phys. B209 (1982) DongJo Kim, LHC and Beyond 2009

10. π 0 -h x E distribution from PYTHIA 2/3/09DongJo Kim, LHC and Beyond 20099 Even with higher x E region Slope gets larger as you go higher pt PYTHIA fit : 0.2<xE<0.8 Unknown quark/gluon contributions increase the systematic higher PYTHIA

11. 2/3/0910  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. DongJo Kim, LHC and Beyond 2009

12. 2/3/09DongJo Kim, LHC and Beyond 200911 What about LHC ? PHENIX measured  p T  pair =3.36  0.09  0.43GeV/c extrapolation to LHC  k 2 T  ~ 6.1 GeV/c

13. 2/3/0912 D(z) from gamma tagged correlation D(z) from gamma tagged correlation leading particle - trigger p Tt xEzxEz p out kTkT away-side fragments - associated particles p Ta h-h: Leading particle does not fix Energy scale. Direct gamma - trigger p Tt xEzxEz p out kTkT away-side fragments - associated particles p Ta  -h: direct gamma does fix Energy scale if no k T DongJo Kim, LHC and Beyond 2009 D(z t )  (z t ) PYTHIA

14. 2/3/0913 00 Direct  PHENIX  s=200 GeV  0 and dir-  assoc. distributions Run 5 p+p @ 200 GeV Statistical Subtraction Method Arbitrary Normalization Exponential slopes still vary with trigger  p T . If dN/dx E  dN/dz then the local slope should be p T  independent. DongJo Kim, LHC and Beyond 2009

15. 2/3/0914 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. 2/3/09DongJo Kim, LHC and Beyond 200915 PYTHIA  -h simulations at RHIC 1) Initial State Radiation/Final State Radiation OFF,  2 =0 GeV/c x E slope is constant 2) IR/FR ON,  2 = 3 GeV/c x E 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)

17. 2/3/0916 Pythia Initial/Final st. radiation & k T Initial/Fina state radiation OFF,  k 2 T  =0 GeV/c Initial/Fina state radiation ON,  k 2 T  =5 GeV/c DongJo Kim, LHC and Beyond 2009 1) Initial State Radiation/Final State Radiation OFF,  2 =0 GeV/c x E slope is constant 2) IR/FR ON,  2 = 5 GeV/c x E 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) Initial State Radiation/Final State Radiation OFF,  2 =0 GeV/c x E slope is constant 2) IR/FR ON,  2 = 5 GeV/c x E slope is raising! Also PYTHIA shows the same trend, though, not as large as in the data, not so trivial even with Direct photons

18. x E distribution comparisons (  -h) 2/3/09DongJo Kim, LHC and Beyond 200917 PHENIX x E distributions and local slopes are compared with PYTHIA and KKP o PHENIX fitting ranges are limited by statistics o Local slopes are getting steeper as Trigger pT gets higher o (1) p T,trigger > ~ 15, PYTHIA were fitted with fixed range,0.1<x E <0.3] o (2)(2)' KKP is much steeper in low xE than PYTHIA PYTHIA Nucl. Phys., 2001, B597, 337-369 Parameters ,  and  from PRD74 (2006) 072002 Nucl. Phys., 2001, B597, 337-369 Parameters ,  and  from PRD74 (2006) 072002 quark vs gluon in KKP (1) (2)’ (2)

19. Local slopes In Various x E ranges 2/3/09DongJo Kim, LHC and Beyond 200918 (1)0.2<x E <0.4 (3) 0.4<x E <0.8 (2) 0.2<x E <0.8 PYTHIA  -u quark jet (Compton) 66 %  -gluon jet (Annihilation) 17 % PYTHIA  -u quark jet (Compton) 66 %  -gluon jet (Annihilation) 17 % Deviation at low p T due to the k T bias. Unlike the di-hadron correlation it asymptotically converges to the correct value ~exp (- 6.2z ) in higher xE region Deviation at low p T due to the k T bias. Unlike the di-hadron correlation it asymptotically converges to the correct value ~exp (- 6.2z ) in higher xE region

20. Need to go higher trigger and x E 2/3/09DongJo Kim, LHC and Beyond 200919 D(z) ~ exp(-6z) D(z) ~ z -  (1-z)  (1+z) -  Parameters ,  and  from PRD74 (2006) 072002 Sami Räsänen’s Talk (afternoon) kT smearing effect

21. quark vs gluon in KKP (1) (2)’ (2) PHENIX xE Bin 2/3/0920 PHENIX dir-  assoc. distributions measures FF Run 5+6 p+p @ 200 GeV Isolated photons DongJo Kim, LHC and Beyond 2009 o PHENIX measures FF in low xE or low ? o PYTHIA and KKP shows the similar trend as data in 5<pTt< 15 GeV o KKP steeper than PYTHIA in low xE region 0.4<xE<0.8 o as xE gets higher, KKP ~ PYTHIA o Finalizing the data and go to higher xE ( pi0 in associated bin )

22. 2/3/0921 Summary and Open issues Inclusive and two-particle correlation measurement in the high-p T 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: k T 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 x E distribution associated with isolated photon is consistent with KKP, only accessible in low x E or region. PYTHIA agrees with Initial/final state radiation on. Need to go higher xE (ala. Pi0 as associated particle ) k T -bias still present - pushes the minimum photon-trigger p T above 10 GeV/c at RHIC and 30 GeV/c at LHC : Sami’s talk. DongJo Kim, LHC and Beyond 2009

23. 22 points are p+p 14 TeV PYTHIA xE distribution, dashed line KKP FF parameterization Nucl. Phys., 2001, B597, 337-369 LHC 14TeV PYTHIA  - gluon jet (Annihilation) 17 %  - u quark jet (Compton) 66 % PYTHIA  - gluon jet (Annihilation) 17 %  - u quark jet (Compton) 66 % 2/3/09DongJo Kim, LHC and Beyond 2009 NLO :hep-ph/9910252

24. More intuitive exercises…. 2/3/0923 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 =  2 min + N 2, so depending on d.o.f can’t really tell from  2 /d.o.f whether I AA gives better constraint than R AA However  2 min /d.o.f=2.8 for I AA fit seems too large to be acceptable. (?) Zhang,Owens,Wang, PRL 98 212301 (2007) NLO pQCD + KKP FF + expanding medium  2 (I AA )  2 (R AA ) Single Di-hadron y (fm) x (fm) T.Renk, K.Eskola, PRC 75, 054910 (2007) DongJo Kim, LHC and Beyond 2009 I AA better than R AA at RHIC and LHC R AA similar situation between RHIC and LHC I AA looks better probe in LHC I AA better than R AA at RHIC and LHC R AA similar situation between RHIC and LHC I AA looks better probe in LHC

25. I AA is better than R AA Gamma-h will be better 2/3/0924 6< p T trig < 10 GeV STAR Preliminary  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 R AA (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 DongJo Kim, LHC and Beyond 2009 Phys.Rev.C75:054910,2007 (1) (2) (3)