25-Jun-15Jan Rak1 Jet properties from dihadron and photon hadron correlations at  s=200 GeV Jan Rak Jyvaskyla University & HIP, Finland for the PHENIX collaboration Jan Rak Jyvaskyla University & HIP, Finland for the PHENIX collaboration

25-Jun-15Jan Rak2 Single inclusive vs two particle correlations Inclusive distributions - despite the great success in the theoretical understanding R AA there is somewhat 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  s=200 GeV

25-Jun-15Jan Rak3 Medium tomography: T. Renk, K. Eskola hep-ph/ nucl-ex/ (Phys. Rev. Lett.) Eskola et al. NPA696 (2001) 729 gluons in Pb / gluons in p x Anti Shadowing

25-Jun-15Jan Rak4 Elastic vs Radiative energy loss S. Wicks et al., nucl-th/ 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 stronger broadening of away-side correlation peak - not seen in the data. Also various models differ significantly in radiative/elastic fraction.

25-Jun-15Jan Rak5 p T broadening only in DIS? Pasquale Di Nezza HERMES ?? away-side widths similar for central and peripheral d+Au rad Au+Au 20-40% rad Au+Au 0-5% rad away-side widths similar for central and peripheral d+Au rad Au+Au 20-40% rad Au+Au 0-5% rad STAR Phys.Rev.Lett.97: < p T (trig) < 15 GeV/c

25-Jun-15Jan Rak6 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

25-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/ MLLA: parton splitting+coherence  angle-ordered parton cascade. Theoretically controlled, experimentally verified approach Medium effects introduced at parton splitting

25-Jun-15Jan Rak8 Azimuthal correlation function in  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 

25-Jun-15Jan Rak9 Jet shape evolution with trigger and assoc. p T Au+Au / p+p  s = 200 GeV arXiv: [nucl-ex] Per-trigger yield vs.  for various trigger and partner p T (p A T  p B T ), arranged by increasing pair momentum (p A T + p B T ) Flat region: celebrated b2b disappearance Punch through region (HR): reappearance at high-p T Shoulder region (SR): Medium induced “Mach cone” Low p T : Enhancement in SR & suppression in HS High p T : Reappearance of away-side jet not due to merging of side peaks

25-Jun-15Jan Rak10 Dihadron correl.  s=200 GeV Truncated mean 1<p Ta <5 GeV/c The width and the truncated  p T  of the shoulder peak are more **similar to the near peak** rather to the away side one The width and the truncated  p T  of the shoulder peak are more **similar to the near peak** rather to the away side one

25-Jun-15Jan Rak11 Mach cone ? Consistent with p+p Narrower by 20% Mach cone significantly narrower (by 20%) as compared to peripheral away peak. Is Mach cone narrower than Delta function??

25-Jun-15Jan Rak12 Details on two-particle correlations in p+p Fragmentation function D(z) and Intrinsic momentum k T Fragmentation function D(z) and Intrinsic momentum k T

25-Jun-15Jan Rak13 Soft + hard QCD radiation k T phenomenology Back-to-back balanced Soft QCD radiation Hard NLO radiation Compton photo-production

25-Jun-15Jan Rak14 Phys. Rev., 1981, D23, 604 PHENIX Resummation techniques: D. Boer and W. Vogelsang, Phys. Rev. D69 (2004) J. Qiu and I. Vitev, Phys. Lett. B570 (2003) 161

25-Jun-15Jan Rak15 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

25-Jun-15Jan Rak16 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 FS parton distribution: 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.

25-Jun-15Jan Rak17 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

25-Jun-15Jan Rak18 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)

25-Jun-15Jan Rak19 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.

25-Jun-15Jan Rak20  k 2 T  and  z t  in 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.

25-Jun-15Jan Rak21 High p T : ref. for HI, resummation, detailed NLO tests High p T : ref. for HI, resummation, detailed NLO tests PHENIX measured  p T  pair =3.36  0.09  0.43GeV/c extrapolation to LHC  k 2 T  36 GeV 2 /c 2 G.G. Barnaföldi, P.Levai

25-Jun-15Jan Rak22 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

25-Jun-15Jan Rak23 Direct  -h Correlations in PHENIX p+p  s=200 GeV Run 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

25-Jun-15Jan Rak24 00 Direct  PHENIX  s=200 GeV  0 and dir-  assoc. distributions Run 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

25-Jun-15Jan Rak25 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

25-Jun-15Jan Rak26 Photon associated yields - “averaged” pQCD k T bias still important, sensitivity to the D(z) shape as expected, the slope is also changing as in the data - parton imbalance. PYTHIA

25-Jun-15Jan Rak27 LO in  S and BDMPS quenching weight F. Arleo, hep-ph/ Absolutely no matching between dNd/z and D(z). This is because of the important contribution of the fragmentation-photon channel, as well as the restricted kinematical z window.

25-Jun-15Jan Rak28 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.