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Jets and High-pT Results from QM 2006: Medium Probing with High Precision

Explore findings from QM 2006 on utilizing jets and high-pT particles to study the medium properties in nuclear collisions, aiming to calibrate energy loss mechanisms, fragmentation, and medium effects on particle production rates. The analysis involves diverse formalisms, centrality dependencies, and energy loss distributions. Investigate the near-side phenomena coupling jet interactions with the medium and uncover hidden effects through detailed analyses of ridge and jet spectra. Ongoing comparisons with theoretical models highlight the evolving understanding of jet-medium interactions.

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Jets and High-pT Results from QM 2006: Medium Probing with High Precision

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  1. Jets and high-pT results from QM 2006 Marco van Leeuwen, LBNL

  2. Motivation A reminder Use jets and high-pT particles to probe the medium Initial production at high-pT is calculable in perturbative QCD and can be calibrated by reference measurements • Goal: measure medium properties • Density, temperature Number of degrees of freedom • Dynamical properties e.g. viscosity • However, we still need to calibrate our probe: • Fragmentation, hadronisation in the vacuum • … and in the medium • Calibrate/constrain energy loss mechanism • Check initial production rates

  3. Direct g at high-pT T. Isobe 0-10% Au+Au Nuclear effects + E-loss (frag g) p+p year-5 Quark-gin-medium conversions RHIC is accumulating p+p stats Agrees with NLO pQCD No enhancement in Au+Au

  4. 0in p+p, d+Au M. Russcher RdA centrality dependence PHENIX, B. Sahlmüller nucl-ex/0610036 2005 p+p Measures Cronin, initial state effects STAR gearing up g, p0 in p+p, d+Au Good agreement with NLO pQCD and PHENIX

  5. RAA for p0: medium density I PHENIX, B. Sahlmüller I. Vitev C. Loizides hep-ph/0608133v2 W. Horowitz Use RAA to extract medium density: I. Vitev: 1000 < dNg/dy < 2000 W. Horowitz: 600 < dNg/dy < 1600 C. Loizides: 6 < < 24 GeV2/fm Statistical analysis to make optimal use of data Caveat: RAA folds geometry, energy loss and fragmentation

  6. What do we learn from RAA? GLV formalism BDMPS formalism ~15 GeV Wicks et al, nucl-th/0512076v2 Renk, Eskola, hep-ph/0610059 DE=15 GeV Energy loss distributions very different for BDMPS and GLV formalisms But RAA similar! Need more differential probes

  7. L-dependence I: azimuthal asymmetry New scaling parameter Le Describes RAA vs angle down to lower pT Le 50-60% No significant loss for Le < 2 fm  Formation time effect? V. Pantuev hep-ph/0506095 V. Pantuev, D. Winter 0-10% PQM: Dainese, Loizides, Paic, Eur Phys J C38, 461 RAA, Sloss vs azimuthal angle Au+Au 200GeV Out of Plane In Plane nucl-ex/0611007 rL(2) scaling sets in pT > 6-8 GeV v2 only described by models above pT> 6 GeV

  8. Quark vs gluon from quark energy loss STAR, L. Ruan STAR, B. Mohanty p/p Curves: X-N. Wang et al PRC70(2004) 031901 PRL 97, 152301 (2006) 90% of p from gluons 40% of p from gluons pT (GeV/c) No sign of stronger gluon energy loss in p/p or p/p ratios Medium modifications to FF? X.N. Wang and X.F. Guo, NPA 696, 788 (2001) W. Liu, C.M. Ko, B.W. Zhang, nucl-th/0607047 Need new calculations, with better baryon FF (AKK)

  9. Energy dependence of RAA 0-12.7% most central Pb+Pb B. Sahlmüller Central Pb+Pb/Au+Au (+ + -)/2 -0.3 < y < 0.7 K. Reygers NA49 preliminary C. Blume NA49 p+C reference preliminary PHENIX Broad agreement between experiments • Lower √sNN, steeper initial spectra • More pronounced ‘Cronin’ effect • Stronger suppression (same RAA for more dilute medium) B. Mohanty

  10. Energy dependence of RAA J. Velkovska p 0 nucl-ex/0504001 RAA at 4 GeV: smooth evolution with √sNN Agrees with energy loss models

  11. Single particle measurements Large set of systematics becoming available • Energy dependenceSPS to RHIC 200 GeV • System size dependence • p+p and d+Au references • RAA vs Npart • RAA vs reaction plane, v2 • Particle type dependence Comparisons to theory ongoing Warrants revisiting some areas of theory?(e.g. baryon fragmentation, path length dependence)

  12. Fragmentation and energy loss I: near-side Dj trigger Di-hadron correlations • What is it ? ‘something’ coupling to long flow ? Can this quantify E-loss ? • How to deal with it?Need to subtract for near-side studies? associated 3 < pt,trigger < 4 GeV pt,assoc. > 2 GeV Au+Au 0-10% preliminary Components • Near-side jet peak • Near-side ridge • Away-side (and v2) Two distinct questions: M. Calderon, J. Putschke Lesson: The near-side jet does interact with the medium

  13. Ridge phenomenology Jet + Ridge Jet Jet + Ridge nucl-ex/0611016 J. Bielcikova PHENIX, A. Sickles PHENIX: drop in baryon-triggered yield for most central events Ridge observed for all trigger particle types After subtraction: jet-yield independent of centrality

  14. Subtracting the ridge II STAR, M. Horner zT = pT,assoc/pT,trig 1 C. Zhang Near side increase at low pT,assoc seen by STAR and PHENIX C. Zhang Subtraction of Dh-independent ‘ridge-yield’ recovers centrality-independent jet yield 1 Vacuum fragmentation after energy loss? Or non-trivial effect hidden by exponential spectra?

  15. pT-dependence of ridge Ridge spectra Jet spectra STAR, J. Putschke Yield (pt,assoc > pt,assoc,cut) Yield (pt,assoc > pt,assoc,cut) pt,assoc,cut pt,assoc,cut Ridge pT-spectra are ‘bulk-like’ Ridge independent of pT,trigger

  16. What is the ridge? Ridge shape STAR, J. Putschke dN/dDh A. Majumder, B. Muller, S. Bass • Radiated gluons, broadened by • Longitudinal flow, Armesto et al, PRL 93 (2004) • QCD magnetic fields, Majumder et al, hep-ph/0611035 • Medium heating + recombination,Chiu & Hwa PRC72, 034903 • Radial flow + trigger bias, Voloshin nucl-th/0312065, Nucl. Phys. A749, 287 hep-ph/0611135 3 < pt,trigger < 4, pt,assoc. > 2 GeV Dh Proposed explanations so far: Jury still out More differential measurements possible? Detailed predictions welcome!

  17. Energy content of Ridge } “Ridge energy” } “Ridge energy” STAR, Phys. Rev. Lett. 95 (2005) 15230 J. Putschke talk 4 < pt,trigger < 6 GeV 6 < pt,trigger < 10 GeV 0.15 < pt,assoc < 4 GeV Near-side modification in published results also due to ridge Energy content of ridge: few GeV

  18. Away-side yields and energy loss Preliminary M. Horner C. Zhang |Dj| > 0.9 8< pTtrig < 15 GeV, PRL 95, 152301 |Dj| > p/2 Clear evolution of away-side suppression with pT,trig, pT,assoc Low pT,trig, pT,assoc: enhancement Increase Q2 for same pT,trig due to energy loss? Caveat: shapes change non-trivially

  19. Di-hadrons: away-side shape Preliminary PHENIX: C. Zhang, N. Grau, J. Jia, E. Vazquez 40-60% 2.5 < pT,trig < 4.0 GeV/c 1.0 < pT,assoc < 2.5 GeV/c nucl-ex/0611019 STAR, M. Horner 0-12% High statistics Run IV data 0-12% Clear evolution peripheral → central: Widening, flattening and ‘dip at p’

  20. Away-side shape: energy dependence 2.5 < pT,trig < 4.0 GeV/c 1.0 < pT,assoc < 2.5 GeV/c PHENIX, C. Zhang Similar trends seen at lower √s=62.4 GeV at RHIC nucl-ex/0611019 CERES, S. Kniege 0-5% 10-20% And at SPS Is this still jet-fragmentation? Compare p+p?

  21. Away-side shape: pT,trig dependence Preliminary 3.0 < pTtrig < 4.0 GeV/c 4.0 < pTtrig < 6.0 GeV/c 6.0 < pTtrig < 10.0 GeV/c 1.3 < pTassoc < 1.8 GeV/c STAR, M. Horner 0-12% 0-12% Away-side flatter for larger pT,trigger But broadening at low pT,assoc persist

  22. Summary of shape evolution dashed=PHENIX, solid=STAR*0.35 away hump System size dependence F. Wang PHENIX, C. Zhang, A. Sickles Npart1/3 Cu+Cu follows trend vs Npart Shape change due to yield increase away from Dj=p

  23. Interpretations of away-side broadening Gluon rad+Sudakov Mach Cone/Shock wave Cherenkov radiation T. Renk, J. Ruppert V. Koch, A. Majumder, X-N. Wang A. Polosa, C. Salgado Stöcker, Casseldery-Solana et al Also: Vitev, Phys. Lett. B630 (2005) Or large kT from radial flow or energy loss Fries, Armesto et al, Hwa Many explanations possible, need more input to conclude

  24. 3-particle correlations Event by event deflection of jets Cone like structure in each event   13 13   0   0   12 12 3-particle Dj-Dj probes away-side structure: Distinguish event-by-event deflection vs conical (Mercedes) emission pattern However: Large backgrounds, background shapes not simple

  25. 3-particle results C. Pruneau, J. Ulery C. Zhang, N. Ajitanand 13 12 3 < pT,trig < 4 GeV/c 1 < pT,assoc < 2 GeV/c Au+Au 0-12% PHENIX Preliminary (12+13)/2- (12-13)/2 Cumulant analysis: Model-independent Non-zero 3-particle structure Jet+background analysis: Model-dependent, more sensitive Off-diagonal peaks consistent with conical emission Different co-ordinates: No ‘deflected-jet peak’ consistent with conical emission Tantalising results! Discussion/comparison of methods between experiments needed

  26. 3-particle correlations at SPS Dfti Dftj Like sign Unlike sign Raw signal CERES, S. Kniege Raw signal 2.5 < pT,trig < 4.0 GeV/c 1.0 < pT,assoc < 2.5 GeV/c 0-5% central All charge background subtracted Strong charge-dependence seen in raw signal Baryon density effect? Off-diagonal peaks seen after background subtraction Indicative of conical emission Mach cones at SPS? Some other mechanism?

  27. Origin of p/p enhancement: PID correlations Away side Near side A. Sickles Preliminary Preliminary Baryon/meson assoc Baryon/meson assoc B/M singles Trigger h±: 2.5 < pT < 4.0GeV/c Near side: increase with centrality Measure particle composition of ridge? Away-side B/M increases strongly with centrality Need comparisons to theory for interpretation Extended pT -range desirable

  28. L,X,W-h correlation J. Bielcikova Near-side yield similar for L, X, W triggered correlations Initial expectation: W dominantly from TTT recombination, no associated yield R. C. Hwa et al., nucl-th/0602024 Revisited (at QM06): possible large contribution from reheated medium Experimental tests pending

  29. Away-side suppression at high pT Theory talk, H. Z. Zhang Emission pointsHydro profile NLO Data: STAR PRL 95, 152301 Di-hadron suppression: smaller surface bias, potentially better differential probe J. Jin, N. Grau, J. Jia, H. Pei T. Renk and Eskola, hep-ph/0610059 Comparison to theory ongoing New data: RAA IAA also in Cu+Cu

  30. g-jet measurements J. Jin, M. Nguyen S. Chattopadhyay, F. Benedosso First results in p+p Consistent with expectations from Pythia Consistent between experiments Promising results: statistical errors can be reduced in coming runs

  31. g-jet in Au+Au Dj distribution Yields J. Jin, M. Nguyen Goal: Measure g-jet suppression in A+A Monochromatic source: differential measurement of jet-quenching X.-N. Wang, Z. Huang, PRC 55:3047, F. Arleo et al JEHP 0411, 009, T. Renk, PRC 71, 034906 First results in Au+Au: consistent with suppression But large statistical uncertainties Upcoming RHIC run will improve statistics for this measurement

  32. Summary/outlook • Impressive amount of new data • Extending pT-reach for inclusives • System size, energy dependence mapped out • Detailed shapes/yields at low, intermediate pT Will this constrain energy loss models? Some open questions: 1) Intermediate pT: origin of ridge and away-side broadening 2) Role of baryon fragmentation vs coalescence(quark/gluon energy loss) Expect developments in near future: Baryon/meson fragmentation at higher pT Improve on g-jet measurements

  33. Future directions g-jet rates RAA at LHC B. Jacak, W. Vogelsang T. Renk Need plot S. Wicks, W. Horowitz RAA at LHC not independent of pT: more sensitive to energy loss distribution Slower rise in BDMPS than GLV g-jet at RHIC-II and LHC … and much more!

  34. Thank you For your attention And to all who provided input and discussion to shape this talk!

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