1. 1 Wolf G. Holzmann Will review critical aspects of jet medium interaction at RHIC (with emphasis on PHENIX results)… … then discuss potential for studying the medium response to jet quenching with the ATLAS detector at the LHC

2. 2  Bjorken  ~ 5 - 15 GeV/fm 3 ~ 35 – 100 ε 0 high energy densities quark dof Evidence for strongly interacting partonic matter is compelling ! Strongly Interacting Matter at RHIC strongly coupled

3. 3 Jets as a tomographic probe of the medium Fragmentation : Jets in h+h collisions Fragmentation : Jets in HI collisions Gyulassy et al., nucl-th/0302077 Jet modification sensitive to gluon densities, path length, … Jet modification sensitive to gluon densities, path length, …. Jets as Tomographic Probes of the Medium!

4. 4 Phys. Rev. Lett. 90, (2003) STAR Jets via: Two Particle Correlations Jets via: Nuclear Modification Factor High p T Jet Modification in Au+Au Strong jet modification observed in Au+Au How is the energy taken up by the medium ?

5. 5 nucl-ex/0507004 T. Renk, J. Ruppert hep-ph/0509036 Strong centrality dependent modification of away-side jet in Au+Au Possible mechanisms mach-cone scenario nucl-th/0406018 Stoecker hep-ph/0411315 Casalderrey-Solana, et al Not the only explanation: Cherenkov gluon radiation: nucl-th/0507063 Koch, Majumder, X.-N. Wang Jets and Flow couple: hep-ph/0411341 Armesto,Salgado,Wiedemann Intermediate p T Jet induced Correlations Can two particle correlations provide constraints for these conjectures?

6. 6 D D Characterize away-side shape via: RMS : measures width of away-side peak Kurtosis : /RMS 2, the 4th central moment, measures “gaussian-ness” of peak (= 3 for Gaussian) D : distance between away-side peak and  from double gaussian fit -> approximates peak-position Let’s take a closer Look at these Shapes

7. 7 Shape modification apparently largely independent of system size and beam energy in range root(s) ~ 64 -200 GeV ! Energy and System Size Dependence of Shape Parameters

8. 8 But medium not too different over this range … Consistent with intermediate p T shape modification being dominated by medium response to jet

9. 9 PHENIX Preliminary [1] Majumder, Wang, nucl-th/0507062 [2] Koch, Majumder, Wang, nucl-th/0507063 Weak p T dependence poses challenges for early gluon Cherenkov radiation models which predicted a strong trend with p T p T Dependence of Shape Parameters

10. 10 Meson vs. Baryon associated partner (for fixed Hadron trigger) PHENIX Preliminary Jet associated mesons and baryons show similar shape modification Jet Associated Identified Particle Correlations

11. 11 If away-side parton is deflected in medium, followed by normal jet fragmentation, expect little change in the away-side jet particle species composition Particle ratios inside jet can give insight! Can PID dependent jet correlations constrain deflection?

12. 12 Meson vs. Baryon associated partner (for fixed Hadron trigger) Jet Associated Baryon to Meson Ratio Baryon/meson ratio trend in jets qualitatively similar to baryon/meson ratio trend of bulk matter. Same mechanism?

13. 13 Remember … Single particle baryon/meson ratio well described by recombination models. Constituent quark scaling of elliptic flow. Greco & Ko nucl-th/0405040

14. 14 Data is not inconsistent with a picture where partons from shock wave “remember” jet direction. The jet and it’s medium excitation are correlated. Jet quenching can introduce 2- body correlations between the jet and the medium: R. Fries, S. Bass and B. Mueller nucl-th/0407102 One Possible Scenario

15. 15 Can we do energy calibrated studies of the medium response? Normal dijet (  o -h): –Trigger bias: E  ~0.75 –Possible surface bias Direct  tagged jet: –No fragmentation: E  ~ E jet –No strong interaction, sensitive to the whole medium Proposed in hep-ph/9605213 ~10 years ago  Fix maximum jet energy that can be transferred to the medium, check for consistency in medium response.

16. 16  generate incl.  -h per trigger yield Methodology in a Nutshell  generate decay  -h per trigger yield (Use pair by pair waiting with MC factor (Use pair by pair waiting with MC factor for prob. That   at given p T decays to for prob. That   at given p T decays to  in p T range of interest)  in p T range of interest)  p+p subtract decay  -h per trigger yield from  -h per trigger yield # inclusive   #  decay  R=

17. 17 PHENIX Preliminary data PYTHIA PYTHIA 6.1 k T = 2.5 GeV  -h Correlations in p+p M. Nguyen (Stony Brook) Reasonable agreement between data and PYTHIA

18. 18 Black: Au+Au Red: p+p 1/N trig dN/d   (rad) Jiamin Jin (Columbia)  -h Correlations in Au+Au We have the tools, we just need the statistics…

19. 19 Possible Modification of Jet Topology hep-ph/0411315 Casalderrey-Solana,Shuryak,Teaney nucl-th/0406018 Stoecker hep-ph/0503158 Muller,Ruppert Wake Effect or “sonic boom” nucl-th/0507063 Koch, Majumder, X.-N. Wang Cherenkov Gluon Radiation wrong p T dependence? wrong particle composition in jet? Two-Particle Correlation data does not proof mach-cone but it seems consistent with it. Bending Jets

20. 20 Jet tomography at LHC Can (and will) do RHIC type studies with better statistics Can (and will) do high p T jet reconstruction (event-by-event jet tomography, event-by-event medium response opposite reconstructed jet…) How can jet studies at the LHC improve on the situation? Truly high p T jets will be produced copiously in Pb+Pb collisions at the LHC

21. 21 My personal detector wish-list for studying medium response to jet quenching at the LHC: Full azimuth and large pseudorapidity coverage to study event shapes opposite a reconstructed jet Excellent capabilities to study global medium properties Excellent calorimetry for full event-by-event jet reconstruction The ATLAS Detector has all these capabilities! Based on the previous slides … Excellent photon identification capability

22. 22 ATLAS Calorimetery Hadronic Barrel Hadronic EndCap EM EndCap EM Barrel Forward Finely segmented calorimeter coverage over full  range and large  range The ATLAS Calorimeter

23. 23 (Di)jets from PYTHIA in Calorimter Towers embedded in HIJING event Measuring Jets in The ATLAS Calorimeter Energetic jets clearly visible over the heavy ion background Large  coverage is important

24. 24 Jet Background Jet Back ground All too wide for single photons  x  = 0.0028 x 0.1 –Segmentation of first EM sampling layer so fine that heavy ion background is ~ negligible (unique at LHC) –Fine  -> rejection of neutral hadron decays –Clean 1st sampling-> prompt  isolation Taking a closer look

25. 25 Two Approaches to Jet Reconstruction in ATLAS A) Seeded Cone Algorithm Original cells Cloned cells Original towers Subtracted cells New towers Reconstructed jets Layer-by-layer subtraction (exclude seeds) Currently also looking at methods to improve algorithm: seed selection, background subtraction, … First approach: use standard p+p cone algorithm with background subtraction

26. 26 Jet Energy Resolution with Seeded Cone Algorithm Study of different event samples embedded into central Pb+Pb HIJING (b=0-2 fm) Results obtained from standard p+p cone algorithm w/ backgr.- subtraction Some recalibration still needed.

27. 27 B) K T Algorithm clusters particles close in phase-space: d ij = min(k 2 ti,k 2 tj )R 2, where R 2 =(  i -  j ) 2 +(  i -  j ) 2 Kt algorithm purposefully mimics a walk backwards along the fragmentation chain for all possible combinations: O(N 3 ) Cacciari et al: “Fast” Kt optimization to O(NlogN) Two Approaches to Jet Reconstruction in ATLAS d iB = k 2 ti

28. 28 How fast is fast? “Fast” Kt algorithm outperforms cone algorithm, Becomes feasible in heavy ion environment! M. Cacciari et al, hep-ph/0512210

29. 29 Real Jets appear as narrow towers “Fake” Jets appear flat and broad Use jet topology to discriminate between jets and background! “Fast” Kt Finder: Discriminating Jets and Background

30. 30 3 4 2 1 3 4 1 2 Initial look seems promising. Other variables can also be constructed. E T,max = maximum E T in calo cell = average E T in calo cell Discriminating Jets and Background: A First Look

31. 31 Can we control the flowing background? Presampler Layer 1Layer 2Layer 3 Yes! Can measure dN/d ϕ in different layers (and sections) of calorimeters e.g. EM Barrel η ϕϕϕϕ ϕϕϕϕ ηηη

32. 32 Reaction Plane Resolution ATLAS has excellent reaction plane resolution!

33. 33   PYTHIA  + jet (75 GeV) superimposed on b=4 fm HIJING Pb+Pb event, full GEANT Jet   +Jet in ATLAS

34. 34   EM Layer 1 E T (GeV) Isolated photon gives clean signal in EM first sampling layer Even in central Pb+Pb ! One (of 64) rows in barrel EM calorimeter 1st sampling layer Δη×Δ ϕ = 0.003x0.1  +Jet in ATLAS

35. 35 PYTHIA  + jet (75 GeV) superimposed on b=4 fm HIJING Pb+Pb event, full GEANT   Background subtracted Jet   +Jet in ATLAS

36. 36  +Jet in ATLAS Direct  triggered angular correlations energy calibrated: - jet studies - mach cone studies Photon bremsstrahlung in jet cone? Many interesting possibilities: let your imagination run wild :-)

37. 37 Summary Di-hadron away-side modification at intermediate pT at RHIC shows characteristics of medium response to jet quenching Consistent with (but no proof of) mach cone type scenario, p T and PID dependent correlations can provide constraints for models ATLAS detector uniquely suited to study jet medium interactions at the LHC Lots of ground work on jet and flow reconstruction in heavy ion Environment (seeded cone algorithm, fast Kt algorithm, different Background subtraction schemes, etc…) being done in ATLAS Studies shown only an “amuse gueule”, see N. Grau’s talk on SundayNew collaborators are welcome!

38. 38 ★ ★ ★ ★ ★ ★ ★ ★ ★ M. Baker, R. Debbe, A. Moraes, R. Nouicer, P. Steinberg, H. Takai, F. Videbaek, S. White Brookhaven National Laboratory, USA J. Dolejsi, M. Spousta Charles University, Prague A. Angerami, B. Cole, N. Grau, W. Holzmann, M. Lelchouk Columbia Unversity, Nevis Laboratories, USA A. Olszewski, B. Toczek, A. Trzupek, B. Wosiek, K. Wozniak IFJ PAN, Krakow, Poland L. Rosselet University of Geneva, Switzerland J. Hill, A. Lebedev, M. Rosati Iowa State University, USA G. Atoian, V. Issakov, H. Kasper, A. Poblaguev, M. Zeller Yale University, USA A. Denisov IHEP, Russia P. Chung, J. Jia, R. Lacey, N N.. Ajitanand Chemistry Department, Stony Brook University, USA V. Pozdnyakov JINR, Dubna, Russia S. Timoshenko MePHI, Moscow, Russia ATLAS HI Working Group

39. 39

40. 40 DELPHI Baryon yield dependence consistent with jet physics in e-e collisions Baryon yield dependence consistent with jet physics in e-e collisions

41. 41 i.e. Zero Yield At Minimum (ZYAM) a 0 is obtained without putting any constraint on the Jet shape by requiring Two source model : Flow (H) & Jet (J) N.N. Ajitanand et al. Phys. Rev. C 72, 011902 (2005) Unconstrained harmonic Constrained High pt particle constrained perpendicular to RP Constraint byte 1 (A) LP 2 (B) Decomposition of Flow and Jet Signals SubtractionExtinction Reliable Decomposition of Flow and Jet Signals via two separate Methods

42. 42 Test of Ansatz Simulation Strong Away-Side Modification in Au+Au Revealed via Both Methods ZYAM subtracted J(  ) Flow extinguished C(  ) = J(  ) Data Both Methods Agree! Phys. Rev. C 72, 011902 (2005)

43. 43 Jet-Pair Fraction:Efficiency corrected Conditional yield (CY): Efficiency corrected Conditional yield (CY): Eff. Corrected pair rate Eff. Corrected Singles yields Recorded values Two Source Model

44. 44 One approach: fix  via N part, vary path length by looking in and out of reaction plane One approach: fix  via N part, vary path length by looking in and out of reaction plane What are the relative influences of: Energy-density Path-length (L, L 2, L a ) What are the relative influences of: Energy-density Path-length (L, L 2, L a ) nucl-ex/0409015 Need to look at problem in several different ways to pin down mechanistic details! D. Winter, WWND2006 STAR, PRL 93 (2004) 252301 Mechanistic Details of Jet Modification

45. 45 No striking difference in modification pattern observed for Au+Au and Cu+Cu at the same Npart! Small differences in yield can cerve to constrain path length dependent models Energy density major actor! Per Trigger Yields can give additional constraints

46. 46

47. 47

48. 48 Jet Position Resolution with Seeded Cone Algorithm Results obtained from standard p+p cone algorithm w/ backgr.- subtraction Some recalibration still needed. Resolutions in  and  for ~50 GeV

49. 49 Jet Background Jet Back ground All too wide for single photons  x  = 0.0028 x 0.1 –Segmentation of first EM sampling layer so fine that heavy ion background is ~ negligible –Fine  -> rejection of neutral hadron decays –Clean 1st sampling-> prompt  isolation The ATLAS Calorimeter

50. 50 The ATLAS Calorimeter Δη×Δ ϕ in LAr Barrel: Layer 1: 0.003x0.1 Layer 2: 0.025x0.025 Layer 3: 0.05x0.025 Finely segmented calorimeter coverage over full  range and large  range

51. 51 Infrared and collinear safeExceptionally suited to study jet sub-structure: - modification of jet topology in Pb+Pb - hard radiation within the jet New ways to distinguish jets and backgroundSystematic cross-check to cone algorithm Advantages of “Fast” Kt Algorithm

52. 52 Possible Modification of Jet Topology hep-ph/0411315 Casalderrey-Solana,Shuryak,Teaney nucl-th/0406018 Stoecker hep-ph/0503158 Muller,Ruppert Wake Effect or “sonic boom” nucl-th/0507063 Koch, Majumder, X.-N. Wang Cherenkov Gluon Radiation hep-ph/0411341 Armesto,Salgado,Wiedemann Jets and Flow couple Can we use jets to probe the equation of state at RHIC?

53. 53 Particle species dependent properties of bulk matter

54. 54 R. Fries, S. Bass and B. Mueller nucl-th/0407102

55. 55 Meson vs. Baryon associated partner (for fixed Hadron trigger) Jet Associated Identified Conditional Yields Different pT trends of jet associated mesons and baryons

56. 56 System size and energy dependence centralperipheral

57. 57 dN ch /d  very similar for Au+Au and Cu+Cu at the same N part ! At RHIC almost all transverse energy goes into particle production Complementary opportunity for jet-tomography: -> fix energy density -> vary path length nucl-ex/0409015 Energy Density versus Path Length Effects

58. 58 No striking difference in modification pattern observed for Au+Au and Cu+Cu at the same Npart! Energy density major actor!  Jets via: Nuclear Modification Factor Jets via: Two Particle Correlations Jet Modification in Au+Au and Cu+Cu

59. 59 We can use three parameters to characterize away side shape 1.RMS : , the width of the distribution, the 2 nd central moment. 2.Kurtosis : /RMS 2, the 4 th central moment, equals to 3 if Gaussian. 3.D : half distance between the double peaks, a double gaussian fit. DD 0-10% 30-40% 60-90 %