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Systematic Study of Di-jet Correlation in Heavy Ion Collisions

Systematic Study of Di-jet Correlation in Heavy Ion Collisions. Outline QCD and the phase transition Evidence for new matter at RHIC Jet studies in d+Au compared to p+p Limit on initial state effects/cold nuclear matter Jet studies in Au+Au compared to p+p and d+Au

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Systematic Study of Di-jet Correlation in Heavy Ion Collisions

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  1. Systematic Study of Di-jet Correlation in Heavy Ion Collisions Outline • QCD and the phase transition • Evidence for new matter at RHIC • Jet studies in d+Au compared to p+p • Limit on initial state effects/cold nuclear matter • Jet studies in Au+Au compared to p+p and d+Au • Hot,dense medium modification • What do we learn about the matter at RHIC? N. Grau Oral Defense 11/21/05

  2. Quantum Chromodynamics Describes forces between hadrons: protons, neutrons ~ 5% of the universe Asymptotic Freedom – as0 as Q2 increases. Allows for perturbative calculations (Feynman Calculus) Hard processes, high Q2, high outgoing energy (Jets) QCD – Theory of Strong Interactions (I) aS(Q) Q (GeV) N. Grau Oral Defense 11/21/05

  3. QCD potential energy between quark pairs Linear at large separations Force is constant! Confinement of partons Not free at large separations QCD – Theory of Strong Interactions (II) N. Grau Oral Defense 11/21/05

  4. Free energy of heavy quark pairs as a function of separation At high temperature Tc ~ 170 MeV ~1012K Potential not linear but flat at large separation F = 0! Deconfinement! Deconfining the Partons N. Grau Oral Defense 11/21/05

  5. Above Tc partons contribute to degrees of freedom Increase energy density, entropy Energy density required ~ 1 GeV/fm3 Dilute, non-interacting gas Quark-Gluon Plasma (QGP) N. Grau Oral Defense 11/21/05

  6. AGS root-s ~ 5 GeV/nucleon SPS root-s ~ 20 GeV/nucleon RHIC root-s ~ 200 GeV/nucleon LHS root-s ~ 7000 GeV/nucleon QCD Phase Diagram N. Grau Oral Defense 11/21/05

  7. Began Operation Summer 2000 Can collide most any system (p+p, d+Au, Au+Au, Cu+Cu, Cu+Au, etc.) Maximum Beam energy for nuclei= 100 GeV/nucleon Relativistic Heavy Ion Collider (RHIC) RHIC from Space N. Grau Oral Defense 11/21/05

  8. RHIC Runs to Date Vacuum and cold nuclear medium effects Run Year Species s1/2 [GeV ] Ldt NTot p-p Equivalent 01 2000 Au+Au 130 1 mb-1 10M 0.04 pb-1 02 2001/2002 Au+Au 200 24 mb-1 170M 1.0 pb-1 p+p 200 0.15 pb-1 3.7G 0.15 pb-1 03 2002/2003 d+Au 200 2.74 nb-1 5.5G 1.1 pb-1 p+p 200 0.35 pb-1 6.6G 0.35 pb-1 04 2003/2004 Au+Au 200 241 mb-1 1.5G 10.0 pb-1 Au+Au 62 9 mb-1 58M 0.36 pb-1 05 2004/2005 Cu+Cu 200 3 nb-1 8.6G 11.9 pb-1Cu+Cu 62 0.19 nb-1 0.4G 0.8 pb-1Cu+Cu 22.5 2.7 mb-1 9M 0.01 pb-1 p+p 200 3.8 pb-1 85B 3.8 pb-1 Hot, dense nuclear medium effects N. Grau Oral Defense 11/21/05

  9. PHENIX Participation N. Grau Oral Defense 11/21/05

  10. PHENIX Detector • Each central arm 90o in azimuth, 70-100o in q • Charged particle tracking outside of the field • Photons with highly segmented EmCal N. Grau Oral Defense 11/21/05

  11. Evidence for New Matter:Energy Density Bjorken Energy Density PRL 87, 052301 (2001) time for system to thermalize (t0 ~ 1 fm/c) ~6.5 fm pR2 eBj >> 15 GeV/fm3 >> necessary N. Grau Oral Defense 11/21/05

  12. Potentially first evidence of radiation from a hot source Red is PHENIX data on photons not from decay Dashed blue  pQCD expectation Black line prediction from pQCD and photons from a source at 500 MeV >> 170 MeV! Need p+p data to compare data with data. PHENIX preliminary Evidence for New Matter:Thermal Radiation N. Grau Oral Defense 11/21/05

  13. Non-overlapping (peripheral) collisions: almond shape overlap region Results in differential pressure gradient in-plane vs. out-of-plane v2 sensitive to the pressure z y x Evidence for New Matter:Pressure N. Grau Oral Defense 11/21/05

  14. All particles flow! Flow reproduced by hydrodynamic (fluid) model assuming an EOS and thermal equilibrium First time ever! Not at AGS or at SPS Evidence for New Matter: Thermal Equilibrium At pT > 2 GeV/c, not just bulk properties but hard scattering (jets) N. Grau Oral Defense 11/21/05

  15. Hydrodynamical models confirm Large pressures Substantial collective motion Viscocity = 0 Heavy quarks flow Expect much less flow since heavy particles rescatter less Strongly interacting, perfect fluid! Greco,Ko,Rapp: PLB595(2004)202 Evidence for New Matter: Strongly-Interacting QGP Non-photonic electrons, dominantly decays of heavy quarks: c and b. N. Grau Oral Defense 11/21/05

  16. Single Particles in Peripheral Collision p0production in p+p Compared with peripheral Au+Au on right # n+n collisions in peripheral Au+Au N. Grau Oral Defense 11/21/05

  17. p+p production scaled to central, head-on collisions Suppression seen in Au+Au compared to the scaled p+p New phenomenon at RHIC! Single Particlesin Central Collisions N. Grau Oral Defense 11/21/05

  18. Single p0 and h are suppressed similarly Partonic phenomenon Direct-photons not suppressed Strong interaction phenomenon Nuclear Modification Factor N. Grau Oral Defense 11/21/05

  19. Gluon bremsstrahlung Like QED bremsstrahlung Radiated gluons interact with the medium as well Single particle suppression related to the gluon density “Jet Quenching” Parton Energy Loss N. Grau Oral Defense 11/21/05

  20. Jet  highly collimated spray of hadrons associated with fragmentation of a fast parton LO diagram in QCD is 22 Easily seen in p+p at root-s 200 GeV Find the jet in Jets in Heavy Ion Collisions Beam View 2 jet event in STAR N. Grau Oral Defense 11/21/05

  21. Exploit property that jets are highly collimated, correlated in azimuth Correlate the hadrons Df ~ 0 intrajet pairs Df ~ p interjet pairs Statistical Determination of Jets:Correlation Functions X.-N. Wang Phys. Rev. D 47, 2754 (1993) N. Grau Oral Defense 11/21/05

  22. Hadron pair (jet) correlations in Au+Au and p+p collisions Near-side unmodified Far-side suppressed Away-side (Interjet) Suppression N. Grau Oral Defense 11/21/05

  23. Incoherent multiple scattering increases the acoplanarity of di-jet pairs Not measured in data because of the suppression of the distribution Broadening of the Away-side Distribution QGP rest frame N. Grau Oral Defense 11/21/05

  24. Suppression Summary as of 2002 • Single particles are strongly suppressed • Away-side correlations are suppressed • Explained in terms of parton energy loss • Color (gluon) density dN/dy ~ 1000 • Expected broadening of the away side • Not measured due to the strong suppression N. Grau Oral Defense 11/21/05

  25. Contribution of this Thesis • First systematic study of jet correlations in nuclear collisions • Study the cold nuclear medium modification in d+Au compared to p+p • Study the hot, dense nuclear medium modification • Extend the pT reach of previous analyses (more jet-like) • Extract other distributions N. Grau Oral Defense 11/21/05

  26. d+Au Au+Au = cold medium = hot and dense medium Initial State Effects Only Initial + Final State Effects Importance of a Systematic Study N. Grau Oral Defense 11/21/05

  27. Single particle spectrum is enhanced and not suppressed! Contrast with the final state suppression of single particles from Au+Au PRL 91, 072303 (2003) Single particle Spectrum in d+Au N. Grau Oral Defense 11/21/05

  28. Multiple elastic scattering increase parton transverse momentum, kT. Smears single particle spectrum Measure kT from final state pair pT Drell-Yan Pair pT of leptons is pair pT of quarks Same for di-jets But the jets fragment kT due to Confinement Hard gluon radiation, i.e. 23 diagrams Cronin Effect: Parton Transverse Momentum N. Grau Oral Defense 11/21/05

  29. Factor of 2 increase from p+p to p+Pb Increases as A1/3 – length of the medium Test to see if this increase is as dramatic at RHIC g+A andp+Aoffset due to an effect from jet reconstruction After offset all data agree point-to-point Direct Measure of kT Broadening in Nuclear Collisions N. Grau Oral Defense 11/21/05

  30. Trigger p0 from 5-10 GeV/c Increase in di-jet distribution should be seen in away-side Correlations in p+p and d+Au N. Grau Oral Defense 11/21/05

  31. Jet Acoplanarity Difference Between p+p and d+Au J. Qiu, I. Vitev PLB 570 161 (2003) p0 – crosses p+/- – circles Multiple scattering model not inconsistent with the data. N. Grau Oral Defense 11/21/05

  32. Why No Significant Difference Between p+p and d+Au? • “Intrinsic” kT larger than the kT due to multiple scattering. • More hard gluon radiation at higher root-s • Could it be recombination (Hwa and Yang)? • Shower (fragmented) partons recombining with the soft (radiated) background • Initially predicted factor of 2 increase in the near angle yield (R. Hwa, C.B. Yang: PRC 70,054902 (2004)) N. Grau Oral Defense 11/21/05

  33. Hwa and Tan, nucl-th/0503060 Ratio to p+p Associated Particle Yields N. Grau Oral Defense 11/21/05

  34. Conclusions About Jet Correlations in d+Au Collisions • Two-particle correlations: d+Au like p+p • Lack of acoplanarity increase • Yields and acoplanarity are consistent with multiple scattering picture • And consistent with recombination picture. • Conclusion: Need different observables N. Grau Oral Defense 11/21/05

  35. Away-side jet seen in correlations with high trigger and associated pT Distribution seen to measure broadening! STAR Preliminary D. Magestro QM2005 Trigger h 8-15 Associated h > 2 Away-Side Jet at High pT in Au+Au 0-20% N. Grau Oral Defense 11/21/05

  36. Far angle widths unchanged from p+p through central Au+Au! 8 < pT(trig) < 15 GeV/c Extracted Away-Side Jet Widths at High pT 5-7 GeV/c(open), 7-10 GeV/c N. Grau Oral Defense 11/21/05

  37. pout,F directly related to kTy From gluon radiation from energy loss/suppression expect kT broadening Correlation widths reveal lack of broadening… assoc. Pout.F Df trigg. pout: Alternative Observable for Broadening Component of associated pT transverse to trigger N. Grau Oral Defense 11/21/05

  38. pout Distribution from jet only Removed flow and background Broadening in kT would be seen in broadening of the pout distribution Distribution is approximately Gaussian: dominated by intrinsic kT pout Distributions 5-7 GeV/c p0 1-10 GeV/c h N. Grau Oral Defense 11/21/05

  39. Fit distribution with Gaussian RMS of Gaussian is unchanged with centrality Lack of broadening is not seen in pout Bands are error due to assumed v2 value Broadening of pout N. Grau Oral Defense 11/21/05

  40. At lower pT suppression of yields in away-side measured Suppression is also evident from STAR data 8 < pT(trig) < 15 GeV/c No broadening but Suppression N. Grau Oral Defense 11/21/05

  41. Measure the yield of particles per trigger as a function of xE Compare central to peripheral distribution, ICP If trigger emitted at the surface ICP ~ RCP If trigger near center ICP ~ 1 Sensitive to differential energy loss between the particles trigg. assoc. Measurement of Yields: dN/dxE N. Grau Oral Defense 11/21/05

  42. xE distribution due to jets only xE Distributions 5-7 GeV/c p0 1-10 GeV/c h N. Grau Oral Defense 11/21/05

  43. Ratio of central 0-20% to peripheral 40-92% Weighted average of the data shows suppression! 11% normalization error band at 1 Point-to-point band error due to v2 Comparison of Central to Peripheral 5-7 GeV/c p0 1-10 GeV/c h N. Grau Oral Defense 11/21/05

  44. Trigger pT dependence of average ICP 20-40%/40-92% (open) 0-20%/40-92% (closed) Suppression increases with centrality, independent of pTtrig. Possible evidence for differential energy loss ICP between RCP and 1 ~RCP ~RCP Centrality and pTDependence of ICP N. Grau Oral Defense 11/21/05

  45. Conclusions from Au+Au Di-jets Correlations • Away-side jet is seen at high pT in central Au+Au • Away-side distribution is not broadened • p+p, d+Au, and Au+Au widths are similar • Away-side yield is suppressed when comparing central and peripheral N. Grau Oral Defense 11/21/05

  46. Implications for Energy Loss Models in Au+Au • Energy loss picture before Aug 2005 • Yield of single particles and away-side pairs from gluon radiation • Broadening is the natural consequence of incoherent multiple scattering • Data shows • Single particles and away-side pairs are suppressed • Distribution is not broadened • What does this imply for energy loss? • Coherent gluon radiation? A cone of radiation? • What property of the medium are the correlations sensitive to? • Color density, something else??? N. Grau Oral Defense 11/21/05

  47. Backup Slides N. Grau Oral Defense 11/21/05

  48. Df Constructing Correlation Functions Real events: events with two particle that are correlated Mixed events: two particles from different events Mixed events represent the pair efficiency and acceptance in Df. Trigger: p0gg Associated: h+/- N. Grau Oral Defense 11/21/05

  49. Total Elliptic flow C(Df) Hard scattering Resonance decays Df (rad) Sources of Correlations N. Grau Oral Defense 11/21/05

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