Jet probes of nuclear collisions: From RHIC to LHC
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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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Jet probes of nuclear collisions: From RHIC to LHC

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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

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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