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The Physics Of the ALICE-EMCalThe Physics Of the ALICE-EMCalRene Bellwied - Wayne State Rene Bellwied - Wayne State

UniversityUniversity

2525thth Winter Workshop On Nuclear Dynamics Winter Workshop On Nuclear DynamicsFeb.1-8, 2009Feb.1-8, 2009

Big Sky, MontanaBig Sky, Montana

Why an EMCal ?Why an EMCal ?

Opportunities in Jet PhysicsOpportunities in Jet Physics

Identified particles in jetsIdentified particles in jets

Conclusions from jet measurementsConclusions from jet measurements

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The ALICE EMCalThe ALICE EMCal

Pb-Sci sampling calorimeterShashlik geometry, APD photo-sensor

||<0.7, ~110o , ~13K towers (x~0.14x0.14)

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From RHIC to LHCFrom RHIC to LHC

from AdS/CFT to pQCDfrom AdS/CFT to pQCD

from sQGP to wQGPfrom sQGP to wQGP

Hirano, Gyulassy (2006)RHIC LHC

see also F.Karsch, arXiv:0804.4148

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Define calorimeter driven physics goalsDefine calorimeter driven physics goals Measure parameters that determine energy loss mechanism (e.g. Measure parameters that determine energy loss mechanism (e.g.

transport coefficient, color charge density, transport coefficient, color charge density, ss))))• Jet reconstruction of hadron jets and gamma jetsJet reconstruction of hadron jets and gamma jets

Determine level of medium response through correlation analysis Determine level of medium response through correlation analysis (jet broadening, jet shape, particle correlations). Specify medium (jet broadening, jet shape, particle correlations). Specify medium parameters (viscosity, speed of sound etc.)parameters (viscosity, speed of sound etc.)• Jet correlation measurementsJet correlation measurements

Determine relative strength of recombination and modified Determine relative strength of recombination and modified fragmentation as a function of transverse momentum. Explore fragmentation as a function of transverse momentum. Explore hadronization.hadronization.• Identified particle measurements in jetsIdentified particle measurements in jets

Determine light / heavy quark energy loss and hadronization Determine light / heavy quark energy loss and hadronization differences.differences.• Jet reconstruction of electron jetsJet reconstruction of electron jets

Determine medium modification in jets related to chiral symmetryDetermine medium modification in jets related to chiral symmetry• Identified resonance measurements in jetsIdentified resonance measurements in jets

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General strategyGeneral strategy

Unique EMCal measurements: jet, photon and Unique EMCal measurements: jet, photon and electron reconstruction, EMCal triggering.electron reconstruction, EMCal triggering.

For particle identified jet measurements and jet For particle identified jet measurements and jet correlations develop interface software that correlations develop interface software that utilizes additional detector components in ALICE utilizes additional detector components in ALICE (TPC,TRD, ITS, PHOS)(TPC,TRD, ITS, PHOS)

potentially an away-side calorimeter in the potentially an away-side calorimeter in the future (J-Cal)future (J-Cal)

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Main Simulation GoalsMain Simulation Goals

Six prioritized subtopics Six prioritized subtopics (according to upcoming Physics Performance Report)(according to upcoming Physics Performance Report)

1.) jet reconstruction1.) jet reconstruction 2.) EMCal triggering 2.) EMCal triggering

3.) direct photon identification and isolation 3.) direct photon identification and isolation

4.) electron and heavy quark tagging 4.) electron and heavy quark tagging

5.) identified jet particles and resonances5.) identified jet particles and resonances

6.) jet correlations6.) jet correlations

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Need full jet reconstructionNeed full jet reconstructiontrigger

trigger

recoil

How to do better? Full jet reconstruction

High pT (leading) hadrons bias towards jets that have not interacted

• indirect measurement of jet quenching• little sensitivity to dynamics and modification of jet structure• little sensitivity to medium response

• Recover full energy/momentum flow → unbiased view of quenching• New observables with sound basis in QCD theory• But how to beat the background problem…?

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Jet Quenching TheoryJet Quenching Theory

Bjorken ’82: elastic energy lossGyulassy, Wang, Plumer ’92: bremsstrahlung dominates

Now: several different approaches, many groups active→ jet quenching measures color charge density, plasma transport coefficients

But quantitative analysis of data requires model buildingCurrent status: large discrepancies (factor~10) in extracted medium parameters (transport coefficients) → ongoing efforts to resolve this

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Fundamental QCD studies:Fundamental QCD studies: distributions – modified (AA) & unmodified (pp) distributions – modified (AA) & unmodified (pp)

In AA: Jet quenching populates lower pIn AA: Jet quenching populates lower pTT hadron spectrum hadron spectrum In pp: QCD models predict particle mass ordering of mean In pp: QCD models predict particle mass ordering of mean

value, BABAR and STAR observe an inverse <value, BABAR and STAR observe an inverse <> ordering of > ordering of KK00

ss and and or por p

R<0.4

=ln(EJet/phadron)

pThadron~2 GeV

for Ejet=100 GeV

RHICequiv.

LHCequiv.

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Tool 1: ‘Realistic Event-generators’ Tool 1: ‘Realistic Event-generators’ Monte Carlo Implementations:Monte Carlo Implementations:

Renk:Renk:medium increases virtuality of partons during evolutionmedium increases virtuality of partons during evolution

PYQUEN (Lokhtin, Snigriev):PYQUEN (Lokhtin, Snigriev):PYTHIA afterburner reduces energy of final state partons and adds PYTHIA afterburner reduces energy of final state partons and adds radiated gluons according to BDMPS expectations.radiated gluons according to BDMPS expectations.

PQM (Dainese, Loizides, Paic):PQM (Dainese, Loizides, Paic):MC implementation of BDMPS quenching weightsMC implementation of BDMPS quenching weights

HIJING (Gyulassy, Wang):HIJING (Gyulassy, Wang):jet and mini-jet production with induced splittingjet and mini-jet production with induced splitting

JEWEL (Zapp, Ingelman, Rathsman, Stachel, Wiedemann):JEWEL (Zapp, Ingelman, Rathsman, Stachel, Wiedemann): parton shower with microscopic description of interactions with mediumparton shower with microscopic description of interactions with medium

q-PYTHIAq-PYTHIA (Armesto, Cunquiero, Salgado, Xiang):(Armesto, Cunquiero, Salgado, Xiang):includes BDMPS-like radiation in modified splitting functionincludes BDMPS-like radiation in modified splitting function

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Tool 1: JEWELTool 1: JEWEL(available at zapp@physi.uni-heidelberg.de)(available at zapp@physi.uni-heidelberg.de)

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Tool 1: q-PYTHIATool 1: q-PYTHIA(http://igfae.usc.es/QatMC)(http://igfae.usc.es/QatMC)

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Jet Reconstruction AlgorithmsJet Reconstruction Algorithms (see talks by E.Bruna & S.Salur)(see talks by E.Bruna & S.Salur)

Seedless, not bound to a circular structure kT: starts from merging low pT particles close

in the phase-space Anti-kT: starts from merging high pT particles

close in the phase-space

Rcone

seed

tracks or towers

R=√(Δφ2+Δη2)

Seed Cone: ‘seed’ (E>Ethreshold) iterative approach

• Seedless Cone (SIS cone): all the particles used as

seeds Splitting/Merging applied

Con

e

Alg

ori

thm

s

Recom

bin

ati

on

A

lgori

thm

s

[Cacciari, Salam, Soyez, arXiv:0802.1189]

[Cacciari, Soyez, arXiv:0704.0292]

outgoing parton

fragmentation

seed

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Tool 2: The FastJet AlgorithmsTool 2: The FastJet Algorithms(see talk by Gregory Soyez)

Suite of modern Colinear-safe and InfRed-safe jet algorithms• seq recomb: kT, Cambridge/Aachen, anti-kT

• cone: SISCone (Seedless InfRed-safe Cone)

Motivated by high precision jets in high lumi p+p at LHC (pileup)• but directly applicable to heavy ion collisions

Two important algorithmic advances:•Numerical tricks → large improvements to processing time vs. event multiplicity → kT was previously unusable at hadron colliders•Rigorous definition of jet area enables much more precise subtraction of diffuse event background

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Recent studies of jet reconstructionRecent studies of jet reconstruction

Attempt to extend the reliability of jet finding algorithm to jet Attempt to extend the reliability of jet finding algorithm to jet energies below 100 GeV. Important for single jets, crucial for energies below 100 GeV. Important for single jets, crucial for jet correlations.jet correlations.

Optimize jet finding algorithm through comparison (FastJet)Optimize jet finding algorithm through comparison (FastJet) Optimize quenching simulations, estimate effects elliptic and Optimize quenching simulations, estimate effects elliptic and

radial flow, hadron corrections, electron conversions, jet-radial flow, hadron corrections, electron conversions, jet-energy correctionenergy correction

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Main studies for jet correlationsMain studies for jet correlations

Simulate possibility of acoplanarity and jet shape measurements based Simulate possibility of acoplanarity and jet shape measurements based on jet reconstruction resolution.on jet reconstruction resolution.

Compare jet axis correlations to leading particle correlations.Compare jet axis correlations to leading particle correlations.

di-jet angle di-jet energy correlation di-jet energy balance

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0 1.2 6.5 88 t [sec]

Collision

L0: Trigger detectors detect collision(V0/T0, PHOS, SPD, TOF, dimuon trigger chambers)

L1: select events according to • centrality• high-pt di-muons• high-pt di-electrons (TRD)• high-pt photons (PHOS/EMCAL)• jets (EMCAL)

L2: reject events due to past/future protection

HLT rejects events containing• no J/psi, Y• no D0• no high-pt photon• no high-pt pi0• no jet, di-jet, -jet

ALICE Trigger HierarchyALICE Trigger Hierarchy

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Recent studies of jet triggeringRecent studies of jet triggering

Attempt to extend the trigger efficiency for jet Attempt to extend the trigger efficiency for jet energies of 50-100 GeV. Check effect of jet energies of 50-100 GeV. Check effect of jet quenchingquenching

Optimize LVL-1 algorithm by taking altering patch Optimize LVL-1 algorithm by taking altering patch size/geometry based on new mapping manipulations size/geometry based on new mapping manipulations (elelctronics).(elelctronics).

Optimize HLT based on EMCalOptimize HLT based on EMCal

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Triggered jet yields in one LHC yearTriggered jet yields in one LHC year

Another factor 5 is possible by triggering TPC at 500 Hz Another factor 5 is possible by triggering TPC at 500 Hz instead of 100 Hz and using EMCal L1/HLT to cut recorded instead of 100 Hz and using EMCal L1/HLT to cut recorded rate down to 100 Hzrate down to 100 Hz

Jet yield in 20 GeV bin

2020

Jet trigger and wrong slope extrapolation can Jet trigger and wrong slope extrapolation can make large difference in particle yield estimatesmake large difference in particle yield estimates

Reach out to 12 GeV/c or 30 GeV/c per year ?

EMCal PPR Original ALICE-PPR

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Direct photons and gamma-jetsDirect photons and gamma-jets

Optimize shower shape algorithms, isolation cutsOptimize shower shape algorithms, isolation cuts

Isolation cut study, PbPb quenched

Shower shape study, PbPb quenched

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Fragmentation PhotonsFragmentation Photons

|| < 0.5

NLO fragmentation photons are a large fraction of the photon x-section

Isolation efficiency in p+p

Pb+Pb: complex problem, no event generator available, just NLO

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Latest gamma-jet simulationsLatest gamma-jet simulations The modification of the fragmentation function can be The modification of the fragmentation function can be

measured for 30 GeV photons in the range of 0.5 < measured for 30 GeV photons in the range of 0.5 < < 3.2. < 3.2. HI Background is the main source of error. Need more HI Background is the main source of error. Need more

studies on: studies on: bkg area, min bkg area, min pT pT cut, jet-jet bkg, pcut, jet-jet bkg, photon hoton IsolationIsolation

Ratio pp / PbPb

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Heavy quark tagging with electronsHeavy quark tagging with electrons

Show electron to heavy meson correspondence in AA Show electron to heavy meson correspondence in AA collisions.collisions.

Optimize e/h discriminationOptimize e/h discrimination Simulate signed DCA method for B-mesonsSimulate signed DCA method for B-mesons

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If coupling stays strong, viscosity stays lowIf coupling stays strong, viscosity stays low(test with heavy flavor v2 and RAA)(test with heavy flavor v2 and RAA)

• At RHIC: heavy flavor quenches and flows like light flavorAt RHIC: heavy flavor quenches and flows like light flavor• Taking the ratio cancels most normalization differences seen previouslyTaking the ratio cancels most normalization differences seen previously• pQCD ratio asymptotically approaches unity,AdS/CFT ratio is flat and pQCD ratio asymptotically approaches unity,AdS/CFT ratio is flat and

many times smaller than pQCDmany times smaller than pQCD

W. Horowitz,arXiv:0710.0595

c/b quenching

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Particle identified jet measurementsParticle identified jet measurementse.g.Sapeta/Wiedemann e.g.Sapeta/Wiedemann (Eur.Phys.J. C55 (2008) 293)(Eur.Phys.J. C55 (2008) 293)::The hadro-chemistry will change in mediumThe hadro-chemistry will change in medium

mediummodification

mediummodification

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ALICE primary track analysis using TPC rdE/dxALICE primary track analysis using TPC rdE/dx

Based on:Based on:tracking efficiencytracking efficiencyrdE/dx efficiencyrdE/dx efficiencyrdE/dx purityrdE/dx purity

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Efficiency and acceptance corrected spectraEfficiency and acceptance corrected spectra

original efficiency & acceptance relativeoriginal efficiency & acceptance relative

correctedcorrected error error

k0

pk

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Accuracy of measurement compared to Accuracy of measurement compared to Sapeta-Wiedemann predictionsSapeta-Wiedemann predictions

SW predictions(MLLA plusJEWEL-typemedium modifications)

Scaled PYTHIAreconstructed in ALICE jets(one LHC yearStatistics)

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Could chiral symmetry restoration Could chiral symmetry restoration decouple from deconfinement ?decouple from deconfinement ?

In lattice QCD comparison quark condensate to Polyakov Loop evolution as a function of T shows that deconfinement and chiral symmetry restoration (CSR) happen at about the same T. But does constituent quark scaling and little evidence for CSR at RHIC indicate decoupling ?

CSR

Peter Petreczky et al. RB, N.Xu (2005)

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Probe chirality through resonances in jetsProbe chirality through resonances in jets(see talk by C. Markert, arXiv:0807.1509)(see talk by C. Markert, arXiv:0807.1509)

Is it possible to have hadron Is it possible to have hadron production prior to hadronization, production prior to hadronization, i.e. can there be a mixed phase of i.e. can there be a mixed phase of degrees of freedom degrees of freedom (partons/hadrons) ?(partons/hadrons) ?

If these hadrons are resonances, If these hadrons are resonances, can they also decay within the can they also decay within the partonic phase or the dense partonic phase or the dense hadronic phase and thus be hadronic phase and thus be medium modified ?medium modified ?

Lattice QCD predicts a cross-over, Lattice QCD predicts a cross-over, thus no mixed phase in the thus no mixed phase in the thermal sense (e.g. water/steam), thermal sense (e.g. water/steam), but the degrees of freedom could but the degrees of freedom could still be mixed if one dof is still be mixed if one dof is governed by thermalization and governed by thermalization and the other dof is governed by the other dof is governed by fragmentationfragmentation

Fragmentation is driven by Fragmentation is driven by fundamental formation timefundamental formation time

partonicmedium

partonicmedium

hadrons/resonances

hadrons/resonances

a mixed d.o.f. system

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Formation Time of Resonances in LHC QGPFormation Time of Resonances in LHC QGP

arXiv:0807.1509arXiv:0807.1509

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Quadrant correlation analysis: Quadrant correlation analysis: requires EMCal for jet reco and trigger requires EMCal for jet reco and trigger

side 1

side 2

near

away

Low pt Low pt High pt High pt

near near side side

No medium or No medium or

late hadronic mediumlate hadronic mediumNo mediumNo medium

away away side side

Late hadronic Late hadronic mediummedium

Partonic or early hadronic Partonic or early hadronic medium (depend on formation medium (depend on formation time) time) CSR ?CSR ?

side side 1&21&2

Late hadonic mediumLate hadonic medium Late or early hadronic mediumLate or early hadronic medium

near side1 away side2

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SummarySummaryThe EMCal in ALICE allows us to perform fundamental QCD studies in pp and AA.

Besides full jet reconstruction and jet triggering, the identification of direct photon and heavy quark jets as well as triggered very high momentum identified mesons, baryons, and resonances round out a program that addresses key issues of QCD such as:

mechanism of energy loss in the mediummodification of particle production in medium chiral symmetry restoration in mediumstrong coupling strength in medium

We expect to complete an EMCal Physics Performance Report by summer ‘09

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Backup slidesBackup slides

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Learn more about the state of Learn more about the state of matter and its differences atmatter and its differences at

RHIC & LHC RHIC & LHC There will be many studies of a more quantitative There will be many studies of a more quantitative

understanding of parton energy loss in a partonic understanding of parton energy loss in a partonic medium medium

There will be many studies of medium properties There will be many studies of medium properties through medium responsethrough medium response

Can we measure a change in coupling and thus a Can we measure a change in coupling and thus a change in the degrees of freedom ? change in the degrees of freedom ?

Can we measure chiral restoration ?Can we measure chiral restoration ?

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High Level TriggerHigh Level TriggerAssembles complete events from all ALICE detectors → run quasi-offline algorithms (e.g. jet reconstruction)

Current developments for EMCal Jet Trigger:• FastJet implemented in Aliroot

– direct usage in HLT

– Jet patch-like HLT algorithm

• HLT developments

– TPC-HLT – new CA tracker (<CPU time> for 14 TeV pp ~ 20 ms)

– Matching TRD+TPC

– Integration of ITS into HLT global track information

– Interface and provide algorithms for prediction mechanisms

– Interface to ECS trigger information and definition of the trigger sets on HLT

• Dedicated triggering/monitoring scheme

– Initial implementation ready to be tested soon

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Particle identified jet measurementsParticle identified jet measurements

Correlate high momentum PID measurements (rdE/dx, V0, hadronic resonances) to Correlate high momentum PID measurements (rdE/dx, V0, hadronic resonances) to triggered jet rates for single hadron or resonance and di-hadron correlation triggered jet rates for single hadron or resonance and di-hadron correlation measurements in jets and between di-jets.measurements in jets and between di-jets.

Determine neutral energy in jet by measuring protons (neutrons) and KDetermine neutral energy in jet by measuring protons (neutrons) and K00ss (for K (for K00

LL) )

very precisely.very precisely.

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Identified particles: goals / plansIdentified particles: goals / plans Determine statistics and resolution of identified particle Determine statistics and resolution of identified particle

measurements in away-side jet cone (non EMCal info) measurements in away-side jet cone (non EMCal info) under EMCal trigger assumption. Measure under EMCal trigger assumption. Measure fragmentation functions and form hadron ratios.fragmentation functions and form hadron ratios.

Compare to models:Compare to models:• Recombination: Recombination:

L. Maiani et al. (hep-ph/0606217)L. Maiani et al. (hep-ph/0606217)• Quenched Fragmentation: Quenched Fragmentation:

Sapeta/Wiedemann (arXiv:0707.3494)Sapeta/Wiedemann (arXiv:0707.3494)

For resonances:For resonances:• Possible chiral effects due to differing formation time for jet and Possible chiral effects due to differing formation time for jet and

bulk resonances. Determine statistics and resolution in bulk resonances. Determine statistics and resolution in quadrants (arXiv:0807.1509). quadrants (arXiv:0807.1509).