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##### Jet properties from dihadron Correlation in PHENIX

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**Jet properties from dihadron Correlation in PHENIX**DongJo Kim Norbert Novitzky, Jiri Kral Sami Räsänen, Jan RakJyväskylä University & Helsinki Institute of Physics, Finland High pT Physics at LHC, Feb 4-7 ,2008 Prague DongJo Kim, Prague High pT 2009**Outline of the talk**• Motivation • RAA, IAA , gamma-h • 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 ? • Compare the data with KKP and PYTHIA • Soft QCD radiations/NLO • Quark/Gluon Fragmentation • -jet momentum imbalance due to the kT smearing • Conclusion and Open Issues DongJo Kim, Prague High pT 2009**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, Prague High pT 2009**leading particle - trigger pTt**away-side fragments - associated particles pTa is the jet fragmentation variable: zt and za pout kT xEz 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, Prague High pT 2009**Phys.Rev.D74:072002,2006**N A p + p jet + jet Azimuthal correlation function in p+p @ s=200 GeV d+Au N jTjet fragmentation transverse momentum F kTparton transverse momentum YA folding ofD(z) and final state parton dist. DongJo Kim, Prague High pT 2009**Two-particle correlations in p+p**Fragmentation function D(z) and Intrinsic momentum kT . DongJo Kim, Prague High pT 2009**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, Prague High pT 2009**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, Prague High pT 2009**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, Prague High pT 2009**π0-h xE distribution from PYTHIA**PYTHIA • PHENIX shows the increasing trend of xE slopes as you go higher pTt • PYTHIA – shows the same trend • Even with higher xE region : PYTHIA fit : 0.2<xE<0.8 DongJo Kim, Prague High pT 2009**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 Base line measurement for the kT broadening Still, we would like to extract FF from our own data -> direct photon-h correl. DongJo Kim, Prague High pT 2009**What about LHC ?**PHENIX measured pTpair=3.360.090.43GeV/c extrapolation to LHC k2T ~ 6.1 GeV/c DongJo Kim, Prague High pT 2009**h-h: Leading particle does not fix Energy scale.**away-side fragments - associated particles pTa leading particle - trigger pTt pout kT xEz -h: direct gamma does fix Energy scale if no kT away-side fragments - associated particles pTa Direct gamma - trigger pTt pout kT xEz D(z) from gamma tagged correlation PYTHIA D(zt) (zt) DongJo Kim, Prague High pT 2009**γ-Jet events**Soft QCD radiation Hard NLO radiation not in PYTHIA Back-to-back balanced Compton photo-production Soft + hard QCD radiation kT phenomenology 13 DongJo Kim, Prague High pT 2009**PHENIX s=200 GeV 0 and dir- assoc. distributions**Run 5 p+p @ 200 GeV Statistical Subtraction Method p0 Exponential slopes still vary with trigger pT. If dN/dxEdN/dz then the local slope should be pT independent. Direct g Arbitrary Normalization Arbitrary Normalization DongJo Kim, Prague High pT 2009**PHENIX s=200 GeV 0 and dir- assoc. distributions**Run 5+6 p+p @ 200 GeV Isolated photons Legend should be corrected, additional *1/10 is missing DongJo Kim, Prague High pT 2009**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, Prague High pT 2009**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, Prague High pT 2009**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, Prague High pT 2009**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, Prague High pT 2009**Need to go higher trigger and xE**D(z) ~ exp(-6z) kT smearing effect D(z) ~ z-a(1-z)b(1+z)-g Parameters a, b and g from PRD74 (2006) 072002 DongJo Kim, Prague High pT 2009**Idea: kT to the partonic final state**New Method We start from unbalanced b-2-b in LAB and ask what boost pT,pair leads to pT,t - pT,a configuration. Results in much simpler formulae. Old Method Start from balanced b-2-b in hard scattering and boost according Gaussian pT,pair Results in complicated numerical integrals See: PRD74 (2006) 072002 21 DongJo Kim, Prague High pT 2009**In partonic level**Lorentz invariance: With assumption of Lorentz invariance, the kinematics can be solved. This distribution is folded over Number distribution of final State hadrons, dn/dpT and Fragmentation function D(z) DongJo Kim, Prague High pT 2009**Effect of kT, D(z) ~ exp(-6z):**Trigger photon’s momentum, pTt, grows DongJo Kim, Prague High pT 2009**Compare γ-hadron and hadron-hadron**γ-hadron associated distributions are always steeper slope seems to approach fragmentation function (FF) in γ-hadron hadron-hadron slope does not represent FF - - - - γ-h h-h 24 DongJo Kim, Prague High pT 2009**Fitting range matters**• In data: zT (or xE) distributions become steeper when pTt • grows, while in the calculation the trend is exactly opposite! • Partonic level needs to be treated carefully? • QCD soft radiation matters in accessible range by PHENIX • Relative yield change from low pT to higher pT • The ways of handling kT + something else (1) low zT: broad gaussian enhances low pT particles strongly (2) medium zT: “optimal” range (3) large zT: shrinking phase phase begins to affect the results (1) (2) (3) DongJo Kim, Prague High pT 2009**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. • Di-hadron and direct photon-h correlations - base line measurement for nuclear modification study: • kT and initial/final state QCD radiation, resummation vs NLO • D(z) : fragmentation function. • 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 with kT. • 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 20~30 GeV/c at LHC. DongJo Kim, Prague High pT 2009**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, Prague High pT 2009**γ – h and h-h correlations**Fold smeared associated distribution over fragmentation function D(z) In following, use fragmentation variable Calculate local slope by negative logarithmic derivative (NLD) DongJo Kim, Prague High pT 2009**PYTHIA guide:**Eq. (229) in Chapter 11.3.3 In PYTHIA: Just an idea, inspired by above: In future, study how relevant this is to obtained slopes ! DongJo Kim, Prague High pT 2009**Trigger bias**Side remark: Imbalance: Mike Tannenbaum For details, see PRD74 (2006) 072002 Right trend in the model!**“Traditional” way to handle intrinsic kT**See J.F. Owens, Rev. Mod. Phys. 59 No.2, 1987 Before kT NOTE! Put in kT from two dimensional gaussian Idea: partons remain at mass shell: However, the pair mass: Integrate over kT’s with gaussian weights. (Turns out: need a cut off when kT ≥ pT of the partonic final state)