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Jet probes of nuclear collisions: From RHIC to LHC

Jet probes of nuclear collisions: From RHIC to LHC. Dan Magestro, The Ohio State University. Midwest Critical Mass October 21-22, 2005. Where’s the LHC?. CERN. CERN. BNL. Where’s the LHC?. CERN. Site of ALICE Experiment. CERN. Jets in hadronic collisions. DM, Hard Probes 2004.

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Jet probes of nuclear collisions: From RHIC to LHC

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  1. Jet probes of nuclear collisions: From RHIC to LHC Dan Magestro, The Ohio State University Midwest Critical Mass October 21-22, 2005

  2. Where’s the LHC? CERN CERN BNL Dan Magestro, Ohio State University

  3. Where’s the LHC? CERN Site of ALICEExperiment CERN Dan Magestro, Ohio State University

  4. Jets in hadronic collisions DM, Hard Probes 2004 • High-energy hadronic collisions: collisions of constituent partons • Each parton carries fraction (x) of hadron’s momentum • “Hard-scattered” outgoing partons back-to-back in azimuth (), • not back-to-back in pseudorapidity () due to different x Side view of collision Transverse plane p p Dan Magestro, Ohio State University

  5. Jets as probes of nuclear collisions - 1  • Partons in vacuum fragment characteristically →calibrated probe Can it be calibrated at LHC? Particle Data Group, PLB 592 (2004) parton = pT(hadron) / pT(parton) Dan Magestro, Ohio State University

  6. Jets as probes of nuclear collisions - 2 QCD hard scattering, jets QGP and hydrodynamic expansion hadronic phase initial state pre-equilibrium hadronization 1 fm/c 5 fm/c 50 fm/c 10 fm/c • Hard parton scatterings early in collision  direct probe • ALICE is the only LHC detector that will measure all HI observables Momentum-space anisotropy QCD hard scattering, jets Heavy particles (charm) Strange baryon spectra Direct photons, leptops Resonance production Nuclear coalescence Nuclear modification HBT interferometry , K, p spectra Particle ratios Dan Magestro, Ohio State University

  7. Observable #1: Inclusive spectra baryons Particle production in AA relative to expectations from p+p RHIC measurements • RHIC: Initial + final state effects  RAB ~ constant STAR, Phys. Rev. Lett. 91 (2003) 072304 B. Cole, QM2005 Dan Magestro, Ohio State University

  8. Observable #1: Inclusive spectra LHC expectation • Significant hardening of spectra • Reduced sensitivity to initial-state kinematic effects • Larger variation of energy-loss with pT Dan Magestro, Ohio State University

  9. Observable #1: Inclusive spectra LHC expectation • RAA exhibits strong pT dependence I. Vitev 5x change! Note: collisional energy loss not considered in this model  even MORE suppression? Dan Magestro, Ohio State University

  10. Jet and dijet measurements at LHC Trigger  Near side Away side 0 /2  0  (radians) ET < 20 GeV ET >(>) 20 GeV Calorimetry, jet-cone algorithms • Try to measure full jet energy • Difficult for lower energy jets dueto background Tracking, 2-particle correlations • Correlate high-pTtrigger particles with associated particles • Sample fragmentation function, neutral energy (~1/3) lost Background contains jets at LHC! Dan Magestro, Ohio State University

  11. Jet correlations and the underlying event PRL 90 (2003) 082302 • Spatial anisotropy in collision induces 2nd-order harmonic p+p Au+Au, 20-40% Dan Magestro, Ohio State University

  12. Observable #2: Back-to-back dijets Pedestal&flow subtracted RHIC results (3)   Higher pT→ Away-side suppression Lower pT→ Away-side enhancement pT(assoc) > 2 GeV/c pT(assoc) > 0.15 GeV/c STAR, PRL 95 (2005) 152301 STAR, PRL 91 (2003) 072304 4 < pT(trig) < 6 GeV/c Dan Magestro, Ohio State University

  13. Observable #2: Back-to-back dijets RHIC results (3)  Higher pT→ Away-side peak emerges: Dijets 8 < pT(trig) < 15 GeV/c DM (STAR), nucl-ex/0510002 Dan Magestro, Ohio State University

  14. Aside: At RHIC we’ve now reached pQCD regime O. Barannikova (STAR), QM2005 • At RHIC, pQCD fragmentation dominates hadron production above ~6 GeV/c R. Fries • At LHC, pQCD dominance predicted to set in a bit higher Dan Magestro, Ohio State University

  15. Observable #2: Back-to-back dijets LHC expectation • Low-ET jets: Two-particle correlations • High-ET jets: Jet reconstuction above background Strong pT dependence of energy loss at LHC requires dijet analyses over full pT range!! Dan Magestro, Ohio State University

  16. Observable #2: Back-to-back dijets LHC expectation – Low-ET • Two-particle correlations necessary • Difficult: large suppression + poor acceptance for away-side jet at low-ET Dan Magestro, Ohio State University

  17. Observable #2: Back-to-back dijets Taken from B. Wyslouch, Hard Probe 2004 LHC expectation – High-ET • Multiple jets + background reduces purity at “intermediate” ET • Trigger capabilities NEEDED to access high ET Dan Magestro, Ohio State University

  18. LHC operations plan • Main objectives: • Terminate installation in Febr. 2007 • First pp collisions in summer 2007, √s = 14 TeV • First long heavy ion (Pb+Pb) run end of 2008, √s = 5.5 TeV • Higher jet rates: first jet-quenching questions can be answered with ~104-105 events, e.g. prediction for strong pT dependence of energy loss • Parallel efforts statistical & reconstructed jets needed to explore full pT range Dan Magestro, Ohio State University

  19. An opportunity for early Pb beam? • 2005 LHC Project Workshop (Chamonix XIV) • Pb ions may be available at very early stage of LHC operation • Jowett (CERN): Likely short Pb “Pilot Run” end of p+p Pilot Run in late 2007 • Depends on ability to commission ion cycle in SPS in 2006 • Luminosity = (few) x 1024 cm-2s-1 ~105 events in < 1 day This could be a great opportunity to answer first (zeroth) energy loss questions with a one-day pilot run Dan Magestro, Ohio State University

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