Jets quenching: what’s next?

1. Jets quenching: what’s next? Peter Jacobs Lawrence Berkeley National Laboratory Jet quenching: what's next?

2. LRP Phases of QCD: Recommendation #1 • 1. Our central goal is a dramatic advance in our understanding of QCD Matter, through quantitative comparison of theory and experiment to determine the properties of the strongly coupled Quark-Gluon Plasma discovered in the initial phase of RHIC operations, and through further exploration of the QCD phase diagram at non-zero baryon density where a critical point has been predicted. The essential requirements for the success of this scientific program are therefore our highest priority: • Effective utilization of the RHIC facility and completion of the ongoing detector upgrade program; • The RHIC II luminosity upgrade, which will enable quantitative study of rare processes; • Strong support for the ongoing theoretical studies of QCD matter, including finite temperature and finite baryon density lattice QCD studies and phenomenological modeling, and an increase of funding to support new initiatives enabled by experimental and theoretical breakthroughs. What does this mean? Jet quenching: what's next?

3. χ2 fit to RAA GLV 1-pvalue ASW Towards precision: measuring PHENIX QM06 B. Sahlmueller et al, nucl-ex/0701060 RAA constrains theory parameters to ~factor 2 Jet quenching: what's next?

4. trigger Yield per trigger pTtrigger>8 GeV/c ? recoil STAR, nucl-ex/0604018 Quantitative jet quenching: dihadron correlations at higher pT… Recoil jet clearly seen above background but at suppressed rate differential measurement of`DE  upper bound on qhat Jet quenching: what's next?

5. Zhang, Owens, Wang and Wang nucl-th/0701045 Df from inclusive and di-hadon suppression Consistent minima for two independent measurements Jet quenching: what's next?

6. RHIC Performance: Run 7 slopeRun7 ~ 2 X slopeRun4 Jet quenching: what's next?

7. Transport Coefficients RHIC I AuAu 2nb-1 (Recorded?) Systematics dominated. Run-4 AuAu 0.2 nb-1 RHIC I ++ Jet quenching: what's next?

8. P. Jacobs and M. van Leeuwen Nucl. Phys A774, 237 (2006) Jet in LHC Heavy Ions Pb+Pb at 5.5 TeV: huge kinematic reach Jet quenching: what's next?

9. Jets at RHIC in the fb era (from Jamie Dunlop’s talk on Monday) STAR PRL 97 (2006) 252001 Jet reco under optimization Data in hand: p+p, Cu+Cu, Au+Au From LHC studies should work for Et>~20-30 GeV Nbin projection from p+p # Jets in bin at 40 GeV Run 6 Cu+Cu: ~50 Run 7 Au+Au: ~1000 600 ub-1, 23 pb-1 p+p equiv. RHIC II: ~50, 000Precise D(z) 2 pb/GeV 40% precision with 0.3 pb-1,half barrel Jet quenching: what's next?

10. c a b d Jet observables • Fully reconstructed single jets • much reduced geometric bias • Jet shape and fragmentation modified by the medium • Observables • “RAA” of jets • Fragmentation function • Acoplanarity of dijets • Jet-g • Jet-Z0 • Multi jets • … ATLAS Jet quenching: what's next?

11. colinear safety: finite calorimeter threshold misses jet on left? infrared safety: one or two jets? Jet reconstruction: generic issues Two broad classes of algorithms: “kT/Durham”: merge all tracks/energy clusters that are nearby in phase space “cone”: fixed shape; stable energy-weighted maxima around seeds; special rules for merging/splitting Jet quenching: what's next?

12. 100 GeV jet in central Pb+Pb Energy (GeV) Jet reconstruction in heavy ion collisions Large backgrounds  optimal resolution using small jet cones R~0.3? • Complex underlying event fluctuations in heavy ion events: • full jet reconstruction is difficult • jet trigger is tricky (large background fluctuations) Jet quenching: what's next?

13. Energy in cone R: background and jets Central Pb+Pb R Soft Background in Jet Cones Large cone radius  large background Radius cut of .4 + pT cut  lowers background  > 80% of Ejet Cone radius R=√(Δη2+ΔΦ2) • Preserve “most” of jet while strongly suppressing bkgd: • pT>2 GeV/c • R~0.4 Jet quenching: what's next?

14. Small cones and jet splitting But why this huge tail for a mono-energetic jet sample with EjetT=100 GeV? Jet quenching: what's next?

15. all particles, R=0.3, pt>2GeV # Jets • input • - Njets,rec=1 • - Njets,rec>=1 highest jet • Njets,rec>=1 mid-cone • - Njets,rec>=1 sum Jet Energy [GeV] Jet splitting/Sub-jet summing fraction of events with Nreconstructed>1 Work in progress Input Jet Energy [GeV] • Small cone radius splits jets - need a correction pass to sum sub-jets and recover jet energy accurately • Internal structure of jet and its modification may also be of great interest… Jet quenching: what's next?

16. kT at a hadron collider: CDF inclusive jets …same performance as modern cone algorithms Jet quenching: what's next?

17. Fast kT PhysLett B641, 57 (2006) • Infrared safe  measure area using zero-energy ghost particles • Potential advantage over cone: smaller effective area, lower integrated background Jet quenching: what's next?

18. Fast kT for LHC Heavy Ions: ATLAS Jet quenching: what's next?

19. Jet quenching pThadron~2 GeV =ln(EJet/phadron) Benchmark measurement: modified fragmentation function • MLLA: good description of vacuum fragmentation (basis of PYTHIA) • introduce medium effects at parton splitting Borghini and Wiedemann, hep-ph/0506218 Jet quenching  fragmentation strongly modified at pThadron~1-5 GeV Jet quenching: what's next?

20. 175 GeV jets in ALICE acceptance Jet quenching Dashed line = no jet quenching Measuremement of modified fragmentation Ratio of purple/red Kinematic reach beyond ~200 GeV Jet quenching: what's next?

21. is a transport property of a medium at T=200 MeV What is learned by probing it with ~200 GeV jets? So what? Jet quenching: what's next?

22. k=E q p (DLA) Evolution of qhat Casalderrey-Solana and Wang, arXiv 0705.1352 High energy jet  small x Large momentum transfer  large scale Jet quenching: what's next?

23. Casalderrey-Solana and Wang arXiv:0705.1352 Evolution of qhat cont’d • Consider jet quenching similar to DIS • jet energy variation probes QGP structure at small and varying x… Jet quenching: what's next?

24. Jet multiplicity dN/d ln(1/x) ln(1/x) Virtuality Q2 Frag Fn modification via elastic scattering • H. Pirner et al (LHC Final Predictions workshop): • Frag Fn modified by scattering in a screened gluon gas (ng~T3) • “evolution” is kinematic in origin Jet quenching: what's next?

25. Direct measurement of qhat: dijet acoplanarityX.-N. Wang jet, g  Jet quenching: what's next?

26. Run-4 AuAu 0.2 nb-1 RHIC I AuAu 2 nb-1 RHIC II AuAu 20 nb-1 q,g Direct Photons at RHIC II g+ jet : photon ET = parton ET at LO g Detailed measurement of modified fragmentation  needs RHIC II luminosity Phys.Rev.C74:034906,2006. Phys.Rev.Lett.77:231-234,1996. Jet quenching: what's next?

27. g/p0 Pb+Pb 104/year p+p hep-ph/0311131 Direct Photons in LHC Heavy Ions This is a difficult and limited measurement cannot be the flagship of the LHC heavy ion program Jet quenching: what's next?

28. Final remarks • Jet quenching is well-established • multiple high-pT signatures with large experimental effects  enables detailed quantitative study • theory: qualitative successes but quantitative gaps • New provocations and speculations: AdS/CFT, Mach cones/whatever,... • Qualitatively new opportunities at RHIC II and LHC • But the Gee-Whiz Era of RHIC Physics is over • now vital to turn our qualitative successes into solid quantitative measurements of hot QCD matter with credible error bars  ongoing, intensive collaboration of experiment and theory Jet quenching: what's next?