High pT Hadron/Jet SuppressionHisayuki Torii, Hiroshima Univ.Workshop at Wuhan02/12/2008

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First Impact on “Jet Quenching” at RHIC• High pT ’s produced at

expected rate▫ No large initial state effects

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STAR, Phys Rev Lett 91, 072304

pTassoc > 2 GeV

• Yield of high pT 0’s suppressed▫ Parton energy loss reflected in

softer fragmentation products

• Suppression of back-to-back high pT hadrons

• Recoil parton is quenched

Systematic Study with High-pT Hadrons• Single Hadron Measurement

• Di-Hadron Measurement (Correlation)

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STAR PRL97(2006)162301

PHENIX PRC78(2008)014901

SKIN Effect in Hadron Measurements4

H.Z.Zhang et al. PRL98(2007)212301 + slides at ATHIC08

High-pT Hadron as Quenching Study•Systematic study of single-hadron and di-

hadron is very critical to understand several effects.▫Flavor Dependence : g – uds – c – b Recombination model at Middle pT Various identified hadrons (or electrons)

▫Skin Effects Single- or Di- or Gamma-hadron Reaction Plane Dependence Nucleus Size Dependence (PbPb vs smaller

nucleus collisions)•I will show a quick review of hadron

measurement at ALICE-PHOS in following several slides.

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Status of Analysis with ALICE-PHOS (1)•0 yield estimates at first (next) LHC run

(p+p)

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PP@14TeV L = 1030 cm-2 s-1 L = 0.5 1029 cm-2 s-1 TPC 200Hz

3 days 45 GeV/c 27 GeV/c 17 GeV/c1 month >60 GeV/c 43 GeV/c 27 GeV/c3 months >60 GeV/c 53 GeV/c 34 GeV/c

Status of Analysis with ALICE-PHOS (2)

Data

AliAnalysisTaskSE

AliAnaPartCorrMaker AliAODCaloTrackReaderESD, AOD, MC

AliAnalisisTaskParticleCorrelation

Data

aodEMCal, aodPHOS,

aodCTS

aodEMCal, aodPHOS,

aodCTS aodParticleCorr

AliAnaPi0derives from

AliAnaPartCorrBaseClas

s

Output: AliAODParticleCorrelation and/orAliAODCaloClustersand/orHistograms

Status of Analysis with ALICE-PHOS (3)• Geometrical Acceptance

▫ Determined by 0 decay kinematics

▫ Flat acceptance at pT>10GeV/c

• Reconstruction Efficiency▫ Because of finite energy and

position resolution of PHOS and steep slope of 0 pT slope, so called “Smearing Effect” appear. This causes the efficiency is not

equal to 100%. The effect depends on the PHOS

calibration Detail analysis of PHOS

calibration is on going.

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Status of Analysis with ALICE-PHOS (4)• Conversion Probability

▫Photons from 0 can be lost due to interactions between other detectors Conversion Loss

▫20% loss is expected• Off-Vertex Contribution

▫0 can be produced at the other detectors Ex. +0 + X 0 + X’

▫<1%

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Further details including eta/omega measurement with PHOS See Renzhuo’s

Talk

Hadron vs Jet MeasurementsLeading Hadron

Reconstructed Jet Bad: Bias in jet finding algorithm

Ideally, the analysis of reconstructed jets will allow us to measure the original parton 4-momentum and the jet structure (longitudinal and transverse).

Measuring the recoil direct photon from +jet processes would provide direct measurement of the parton energy (@LO)

“Golden” measurement, but difficult due to low rate and huge backgrounds

BAD: Surface emission “trigger bias” leading to Small sensitivity of RAA to variations of transport

parameter qhat. Yields only lower limit on color charge density. For increasing in medium path length L leading particle

is less and less correlated with jet 4-momentum. Good

No experimental bias unlike jet identification

Gluon vs Quark Jets• Naively, gluon jet is quenched more than quark jet

▫Strong Interaction Color Factor C(A) : C(F) = 3 : 4/3• Comparison between gluon and quark

Extreame test of quenching effect

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Gluon Dominant

Single/Di-Hadrons/Jets

Photon-Jets

Quark Dominant

PYTHIA 5.5TeV PYTHIA 5.5TeV

PYTHIA Pi0 at 14TeV

GOLDEN measurement

An Idea of How to See Gluon/Quark 12

Gluon Dominant

Single/Di-Jets Photon-Jets

Quark Dominant

PYTHIA 5.5TeV PYTHIA 5.5TeV

Statistics:Good

(<150-200GeV/c : EMCal)

Statistics:Bad

(<40GeV/c with EMCAL)

Caveat: Difficult due to huge background. Hard to

obtain a reference measurement at p+p

Upgrade of EMCal with Trigger is critial

An Idea of How to See Gluon/Quark 13

Gluon Dominant

Single/Di-Jets Photon-Jets

Quark Dominant

PYTHIA 5.5TeV PYTHIA 5.5TeV

Tri-Jets

More Gluon?

Naively, the gluon/quark ratio is much more than that in di-jets because of additional gluon radiation

Statistics:Good

(up to 150-200GeV/c)

Statistics:Bad

(up to 40GeV/c)

Caveat: Difficult due to huge background. Hard to

obtain a reference measurement at p+p

Statistics:???

EMCal with TriggerWhat do we need?Upgrade of ALICE?

An NLO-pQCD Event Generator• GR@PPA

▫ “GRace At Proton-Proton/Antiproton collisions”▫ One of existing NLO-pQCD event generator in the world.▫ Developed by KEK theory group.▫ Fortran▫ Fragmentation by string model in PYTHIA▫ Familiar interface for PYTHIA fortrun users.▫ Many channels including 2,3,4jets.

• Analysis▫ Instead of employing a jet finding algorithm (kT or cone),

following cuts were applied on the 2 or 3 parton kinematics. pT of each parton > 10GeV/c Rapidity of all parton < +-1.4 Distance between two partons > 0.4 in eta/phi space.

▫ This is first view of tri-jet effect.

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Ratio of Tri-Jets and Di-Jets by GR@PPA

• 3-jets contribution is suppressed strongly at pt<50GeV/c because of requirement on jets

• Gluon/Quark jets ratio decrease from 12% to 9% at 20GeV/c▫ A little smaller than naïve expectation▫ More detail analysis is on going.

• Question : How the surface effect is different between tri and di?

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Just an Idea about How to Measure?• Inclusive/Di-jet estimation exist

with EMCal• Inclusive Jets measurement at

EMCal by two different trigger▫ Triggered by another jets

(detected by TPC) at 180deg direction in azimuthal plane.

▫ Triggered by two jets (detected by TPC) not at 180deg direction in azimuthal plane

• Both statistics must be enough up to 160GeV/c▫ Jet shape analysis▫ Hadron multiplicity inside

the jets• Question: How to define

the scale of jet?

10k/year

From ALICE-EMCal Proporsal

Summary•Systematic study of single/di-hadron measurements

▫Critical to separate various effect▫High pt hadron measurement with PHOS is on going

•Jet measurement▫Sensitive to modification of fragmentation function▫Gluon/Quark separation is critical test on quenching

effect, so gluon density in QGP•Tri-Jet for gluon jet enhancement

▫An idea of enhancing gluon jets more than single/di-jet measurement Tri-Jet

▫First estimate of yield: Comparable with Di-jet.▫Upgrade at ALICE?

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