1 / 27

Analysis of Direct Photon Associated Spectra from RHIC to LHC

This study examines the spectra of direct photons associated with high-energy collisions at RHIC and LHC, exploring open questions and various contributions to be understood.

kylesa
Download Presentation

Analysis of Direct Photon Associated Spectra from RHIC to LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Analysis of the Direct photon associated spectra from RHIC to LHC DongJo Kim Rafael Diaz, 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 • 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 • 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. 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, LHC and Beyond 2009

  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 DongJo Kim, LHC and Beyond 2009

  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, LHC and Beyond 2009

  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, LHC and Beyond 2009

  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, LHC and Beyond 2009

  8. 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

  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, LHC and Beyond 2009

  10. 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

  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, LHC and Beyond 2009

  12. 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

  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, LHC and Beyond 2009

  14. π0-h xE distribution from PYTHIA Even with higher xE region Slope gets larger as you go higher pt PYTHIA fit : 0.2<xE<0.8 DongJo Kim, LHC and Beyond 2009

  15. 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

  16. 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

  17. 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, LHC and Beyond 2009

  18. Soft QCD radiation Hard NLO radiation Soft + hard QCD radiation kT phenomenology Back-to-back balanced Compton photo-production DongJo Kim, LHC and Beyond 2009

  19. 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

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

  21. 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

  22. 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

  23.  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, LHC and Beyond 2009

  24. xE distribution comparisons (-h) PYTHIA • 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 • pT,trigger > ~ 15 , PYTHIA were fitted with fixed range ,0.1<xE<0.3] • KKP is much steeper in low xE than PYTHIA DongJo Kim, LHC and Beyond 2009

  25. 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

  26. 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

  27. 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. • We are at the beginning of hard-probes exploration in heavy ion environment - LHC (supported by RHIC) will be fun ! DongJo Kim, LHC and Beyond 2009

More Related