1. 1 The Physics Of the ALICE-EMCal Rene Bellwied - Wayne State University 25 th Winter Workshop On Nuclear Dynamics Feb.1-8, 2009 Big Sky, Montana Why an EMCal ? Opportunities in Jet Physics Identified particles in jets Conclusions from jet measurements

2. 2 The ALICE EMCal Pb-Sci sampling calorimeter Shashlik geometry, APD photo-sensor |  |<0.7,  ~110 o, ~13K towers (  x  ~0.14x0.14)

3. 3 From RHIC to LHC from AdS/CFT to pQCD from sQGP to wQGP Hirano, Gyulassy (2006) RHIC LHC see also F.Karsch, arXiv:0804.4148

4. 4 Define calorimeter driven physics goals Measure parameters that determine energy loss mechanism (e.g. transport coefficient, color charge density,  s )) Measure parameters that determine energy loss mechanism (e.g. transport coefficient, color charge density,  s )) Jet reconstruction of hadron jets and gamma jetsJet reconstruction of hadron jets and gamma jets Determine level of medium response through correlation analysis (jet broadening, jet shape, particle correlations). Specify medium parameters (viscosity, speed of sound etc.) Determine level of medium response through correlation analysis (jet broadening, jet shape, particle correlations). Specify medium parameters (viscosity, speed of sound etc.) Jet correlation measurementsJet correlation measurements Determine relative strength of recombination and modified fragmentation as a function of transverse momentum. Explore hadronization. Determine relative strength of recombination and modified fragmentation as a function of transverse momentum. Explore hadronization. Identified particle measurements in jetsIdentified particle measurements in jets Determine light / heavy quark energy loss and hadronization differences. Determine light / heavy quark energy loss and hadronization differences. Jet reconstruction of electron jetsJet reconstruction of electron jets Determine medium modification in jets related to chiral symmetry Determine medium modification in jets related to chiral symmetry Identified resonance measurements in jetsIdentified resonance measurements in jets

5. 5 General strategy Unique EMCal measurements: jet, photon and electron reconstruction, EMCal triggering. Unique EMCal measurements: jet, photon and electron reconstruction, EMCal triggering. For particle identified jet measurements and jet correlations develop interface software that utilizes additional detector components in ALICE (TPC,TRD, ITS, PHOS) For particle identified jet measurements and jet correlations develop interface software that utilizes additional detector components in ALICE (TPC,TRD, ITS, PHOS) potentially an away-side calorimeter in the future (J-Cal) potentially an away-side calorimeter in the future (J-Cal)

6. 6 Main Simulation Goals Six prioritized subtopics Six prioritized subtopics (according to upcoming Physics Performance Report) 1.) jet reconstruction 2.) EMCal triggering 3.) direct photon identification and isolation 4.) electron and heavy quark tagging 5.) identified jet particles and resonances 6.) jet correlations

7. 7 Need full jet reconstruction trigger recoil How to do better? Full jet reconstruction High p T (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…?

8. 8 Jet Quenching Theory Bjorken ’82: elastic energy loss Gyulassy, 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 building Current status: large discrepancies (factor~10) in extracted medium parameters (transport coefficients) → ongoing efforts to resolve this

9. 9 Fundamental QCD studies:  distributions – modified (AA) & unmodified (pp) In AA: Jet quenching populates lower p T hadron spectrum In AA: Jet quenching populates lower p T hadron spectrum In pp: QCD models predict particle mass ordering of mean  value, BABAR and STAR observe an inverse ordering of K 0 s and or p In pp: QCD models predict particle mass ordering of mean  value, BABAR and STAR observe an inverse ordering of K 0 s and or p R<0.4  =ln( E Jet / p hadron ) p T hadron ~2 GeV for E jet =100 GeV RHIC equiv. LHC equiv.

10. 10 Tool 1: ‘Realistic Event-generators’ Monte Carlo Implementations: Renk: medium increases virtuality of partons during evolution PYQUEN (Lokhtin, Snigriev): PYTHIA afterburner reduces energy of final state partons and adds radiated gluons according to BDMPS expectations. PQM (Dainese, Loizides, Paic): MC implementation of BDMPS quenching weights HIJING (Gyulassy, Wang): jet and mini-jet production with induced splitting JEWEL (Zapp, Ingelman, Rathsman, Stachel, Wiedemann): parton shower with microscopic description of interactions with medium q-PYTHIA (Armesto, Cunquiero, Salgado, Xiang): includes BDMPS-like radiation in modified splitting function

11. 11 Tool 1: JEWEL (available at zapp@physi.uni-heidelberg.de)

12. 12 Tool 1: q-PYTHIA (http://igfae.usc.es/QatMC)

13. 13 Jet Reconstruction Algorithms (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 R cone seed tracks or towers R=√(Δφ 2 +Δη 2 ) Seed Cone: ‘seed’ (E>Ethreshold) iterative approach Seedless Cone (SIS cone): all the particles used as seeds Splitting/Merging applied Cone Algorithms Recombination Algorithms [Cacciari, Salam, Soyez, arXiv:0802.1189] [Cacciari, Soyez, arXiv:0704.0292] outgoing parton fragmentation seed

14. 14 Tool 2: The FastJet Algorithms (see talk by Gregory Soyez) Suite of modern Colinear-safe and InfRed-safe jet algorithms seq recomb: k T, Cambridge/Aachen, anti-k T 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: 1.Numerical tricks → large improvements to processing time vs. event multiplicity → k T was previously unusable at hadron colliders 2.Rigorous definition of jet area enables much more precise subtraction of diffuse event background

15. 15 Recent studies of jet reconstruction Attempt to extend the reliability of jet finding algorithm to jet energies below 100 GeV. Important for single jets, crucial for jet correlations. Attempt to extend the reliability of jet finding algorithm to jet energies below 100 GeV. Important for single jets, crucial for jet correlations. Optimize jet finding algorithm through comparison (FastJet) Optimize jet finding algorithm through comparison (FastJet) Optimize quenching simulations, estimate effects elliptic and radial flow, hadron corrections, electron conversions, jet- energy correction Optimize quenching simulations, estimate effects elliptic and radial flow, hadron corrections, electron conversions, jet- energy correction

16. 16 Main studies for jet correlations Simulate possibility of acoplanarity and jet shape measurements based on jet reconstruction resolution. Simulate possibility of acoplanarity and jet shape measurements based 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

17. 17 0 1.26.5 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 Hierarchy

18. 18 Recent studies of jet triggering Attempt to extend the trigger efficiency for jet energies of 50-100 GeV. Check effect of jet quenching Attempt to extend the trigger efficiency for jet energies of 50-100 GeV. Check effect of jet quenching Optimize LVL-1 algorithm by taking altering patch size/geometry based on new mapping manipulations (elelctronics). Optimize LVL-1 algorithm by taking altering patch size/geometry based on new mapping manipulations (elelctronics). Optimize HLT based on EMCal Optimize HLT based on EMCal

19. 19 Triggered jet yields in one LHC year Another factor 5 is possible by triggering TPC at 500 Hz instead of 100 Hz and using EMCal L1/HLT to cut recorded rate down to 100 Hz Another factor 5 is possible by triggering TPC at 500 Hz instead of 100 Hz and using EMCal L1/HLT to cut recorded rate down to 100 Hz Jet yield in 20 GeV bin

20. 20 Jet trigger and wrong slope extrapolation can make large difference in particle yield estimates Reach out to 12 GeV/c or 30 GeV/c per year ? EMCal PPR Original ALICE-PPR

21. 21 Direct photons and gamma-jets Optimize shower shape algorithms, isolation cuts Optimize shower shape algorithms, isolation cuts Isolation cut study, PbPb quenched Shower shape study, PbPb quenched

22. 22 Fragmentation 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

23. 23 Latest gamma-jet simulations The modification of the fragmentation function can be measured for 30 GeV photons in the range of 0.5 <  < 3.2. The modification of the fragmentation function can be measured for 30 GeV photons in the range of 0.5 <  < 3.2. HI Background is the main source of error. Need more studies on: bkg area, min pT cut, jet-jet bkg, p hoton Isolation HI Background is the main source of error. Need more studies on: bkg area, min pT cut, jet-jet bkg, p hoton Isolation Ratio pp / PbPb

24. 24 Heavy quark tagging with electrons Show electron to heavy meson correspondence in AA collisions. Show electron to heavy meson correspondence in AA collisions. Optimize e/h discrimination Optimize e/h discrimination Simulate signed DCA method for B-mesons Simulate signed DCA method for B-mesons

25. 25 If coupling stays strong, viscosity stays low (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 many times smaller than pQCDpQCD ratio asymptotically approaches unity,AdS/CFT ratio is flat and many times smaller than pQCD W. Horowitz, arXiv:0710.0595 c/b quenching

26. 26 Particle identified jet measurements e.g.Sapeta/Wiedemann (Eur.Phys.J. C55 (2008) 293) : The hadro-chemistry will change in medium medium modification medium modification

27. 27 ALICE primary track analysis using TPC rdE/dx Based on: tracking efficiency rdE/dx efficiency rdE/dx purity

28. 28 Efficiency and acceptance corrected spectra original efficiency & acceptance relative original efficiency & acceptance relative corrected error corrected error k0pkk0pk

29. 29 Accuracy of measurement compared to Sapeta-Wiedemann predictions SW predictions (MLLA plus JEWEL-type medium modifications) Scaled PYTHIA reconstructed in ALICE jets (one LHC year Statistics)

30. 30 Could chiral symmetry restoration 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)

31. 31 Probe chirality through resonances in jets (see talk by C. Markert, arXiv:0807.1509) Is it possible to have hadron production prior to hadronization, i.e. can there be a mixed phase of degrees of freedom (partons/hadrons) ? Is it possible to have hadron production prior to hadronization, i.e. can there be a mixed phase of degrees of freedom (partons/hadrons) ? If these hadrons are resonances, can they also decay within the partonic phase or the dense hadronic phase and thus be medium modified ? If these hadrons are resonances, can they also decay within the partonic phase or the dense hadronic phase and thus be medium modified ? Lattice QCD predicts a cross-over, thus no mixed phase in the thermal sense (e.g. water/steam), but the degrees of freedom could still be mixed if one dof is governed by thermalization and the other dof is governed by fragmentation Lattice QCD predicts a cross-over, thus no mixed phase in the thermal sense (e.g. water/steam), but the degrees of freedom could still be mixed if one dof is governed by thermalization and the other dof is governed by fragmentation Fragmentation is driven by fundamental formation time Fragmentation is driven by fundamental formation time partonic medium partonic medium hadrons/ resonances hadrons/ resonances a mixed d.o.f. system

32. 32 Formation Time of Resonances in LHC QGP arXiv:0807.1509

33. 33 Quadrant correlation analysis: requires EMCal for jet reco and trigger side 1 side 2 near away Low pt High pt near side No medium or late hadronic medium No medium away side Late hadronic medium Partonic or early hadronic medium (depend on formation time) CSR ? side 1&2 Late hadonic medium Late or early hadronic medium near side1 away side2

34. 34Summary The 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 medium modification of particle production in medium chiral symmetry restoration in medium strong coupling strength in medium We expect to complete an EMCal Physics Performance Report by summer ‘09

35. 35 Backup slides

36. 36 Learn more about the state of matter and its differences at RHIC & LHC There will be many studies of a more quantitative understanding of parton energy loss in a partonic medium There will be many studies of a more quantitative understanding of parton energy loss in a partonic medium There will be many studies of medium properties through medium response There will be many studies of medium properties through medium response Can we measure a change in coupling and thus a change in the degrees of freedom ? Can we measure a change in coupling and thus a change in the degrees of freedom ? Can we measure chiral restoration ? Can we measure chiral restoration ?

37. 37 High Level Trigger Assembles 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 ( 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

38. 38 Particle identified jet measurements Correlate high momentum PID measurements (rdE/dx, V0, hadronic resonances) to triggered jet rates for single hadron or resonance and di-hadron correlation measurements in jets and between di-jets. Correlate high momentum PID measurements (rdE/dx, V0, hadronic resonances) to triggered jet rates for single hadron or resonance and di-hadron correlation measurements in jets and between di-jets. Determine neutral energy in jet by measuring protons (neutrons) and K 0 s (for K 0 L ) very precisely. Determine neutral energy in jet by measuring protons (neutrons) and K 0 s (for K 0 L ) very precisely.

39. 39 Identified particles: goals / plans Determine statistics and resolution of identified particle measurements in away-side jet cone (non EMCal info) under EMCal trigger assumption. Measure fragmentation functions and form hadron ratios. Determine statistics and resolution of identified particle measurements in away-side jet cone (non EMCal info) under EMCal trigger assumption. Measure fragmentation functions and form hadron ratios. Compare to models: Compare to models: Recombination:Recombination: L. Maiani et al. (hep-ph/0606217) Quenched Fragmentation:Quenched Fragmentation: Sapeta/Wiedemann (arXiv:0707.3494) For resonances: For resonances: Possible chiral effects due to differing formation time for jet and bulk resonances. Determine statistics and resolution in quadrants (arXiv:0807.1509).Possible chiral effects due to differing formation time for jet and bulk resonances. Determine statistics and resolution in quadrants (arXiv:0807.1509).