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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
22
The ALICE EMCalThe ALICE EMCal
Pb-Sci sampling calorimeterShashlik geometry, APD photo-sensor
||<0.7, ~110o , ~13K towers (x~0.14x0.14)
33
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
44
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
55
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)
66
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
77
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…?
88
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
99
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.
1010
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
1111
Tool 1: JEWELTool 1: JEWEL(available at [email protected])(available at [email protected])
1212
Tool 1: q-PYTHIATool 1: q-PYTHIA(http://igfae.usc.es/QatMC)(http://igfae.usc.es/QatMC)
1313
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
1414
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
1515
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
1616
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
1717
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
1818
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
1919
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
2121
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
2222
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
2323
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
2424
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
2525
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
2626
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
2727
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
2828
Efficiency and acceptance corrected spectraEfficiency and acceptance corrected spectra
original efficiency & acceptance relativeoriginal efficiency & acceptance relative
correctedcorrected error error
k0
pk
2929
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)
3030
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)
3131
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
3232
Formation Time of Resonances in LHC QGPFormation Time of Resonances in LHC QGP
arXiv:0807.1509arXiv:0807.1509
3333
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
3434
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
3535
Backup slidesBackup slides
3636
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 ?
3737
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
3838
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.
3939
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).