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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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slide1
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
Where’s the LHC?

CERN

CERN

BNL

Dan Magestro, Ohio State University

where s the lhc1
Where’s the LHC?

CERN

Site of ALICEExperiment

CERN

Dan Magestro, Ohio State University

jets in hadronic collisions
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

jets as probes of nuclear collisions 1
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

jets as probes of nuclear collisions 2
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

observable 1 inclusive spectra
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

observable 1 inclusive spectra1
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

observable 1 inclusive spectra2
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

jet and dijet measurements at lhc
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

jet correlations and the underlying event
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

observable 2 back to back dijets
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

observable 2 back to back dijets1
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

aside at rhic we ve now reached pqcd regime
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

observable 2 back to back dijets2
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

observable 2 back to back dijets3
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

observable 2 back to back dijets4
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

lhc operations plan
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

an opportunity for early pb beam
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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