The Physics Of the ALICE-EMCal Rene Bellwied - Wayne State University

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

2. The ALICE EMCal • Pb-Sci sampling calorimeter • Shashlik geometry, • APD photo-sensor • |h|<0.7, Df~110o , ~13K towers (DhxDf~0.14x0.14)

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

4. Define calorimeter driven physics goals • Measure parameters that determine energy loss mechanism (e.g. transport coefficient, color charge density, as)) • Jet 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.) • Jet correlation measurements • Determine relative strength of recombination and modified fragmentation as a function of transverse momentum. Explore hadronization. • Identified particle measurements in jets • Determine light / heavy quark energy loss and hadronization differences. • Jet reconstruction of electron jets • Determine medium modification in jets related to chiral symmetry • Identified resonance measurements in jets

5. General strategy • 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) • potentially an away-side calorimeter in the future (J-Cal)

6. Main Simulation Goals • 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. Need full jet reconstruction • High pT (leading) hadronsbias 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 trigger trigger How to do better? Full jet reconstruction recoil • 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. 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. Fundamental QCD studies:x distributions – modified (AA) & unmodified (pp) pThadron~2 GeV for Ejet=100 GeV =ln(EJet/phadron) R<0.4 LHC equiv. RHIC equiv. In AA: Jet quenching populates lower pT hadron spectrum In pp: QCD models predict particle mass ordering of mean x value, BABAR and STAR observe an inverse <x> ordering of K0s and L or p

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

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

13. Jet Reconstruction Algorithms(see talks by E.Bruna & S.Salur) seed • Seed Cone: • ‘seed’ (E>Ethreshold) • iterative approach • Seedless Cone (SIS cone): • all the particles used as seeds • Splitting/Merging applied fragmentation tracks or towers Cone Algorithms outgoing parton Rcone seed R=√(Δφ2+Δη2) [Cacciari, Soyez, arXiv:0704.0292] • 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 Recombination Algorithms [Cacciari, Salam, Soyez, arXiv:0802.1189]

14. Tool 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

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. • Optimize jet finding algorithm through comparison (FastJet) • Optimize quenching simulations, estimate effects elliptic and radial flow, hadron corrections, electron conversions, jet-energy correction

16. Main studies for jet correlations di-jet angle di-jet energy correlation di-jet energy balance • Simulate possibility of acoplanarity and jet shape measurements based on jet reconstruction resolution. • Compare jet axis correlations to leading particle correlations.

17. ALICE Trigger Hierarchy 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 88 t [sec] 0 1.2 6.5

18. Recent studies of jet triggering • 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 HLT based on EMCal

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 Jet yield in 20 GeV bin

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

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

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

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

25. If coupling stays strong, viscosity stays low(test with heavy flavor v2 and RAA) c/b quenching W. Horowitz, arXiv:0710.0595 • At RHIC: heavy flavor quenches and flows like light flavor • Taking the ratio cancels most normalization differences seen previously • pQCD ratio asymptotically approaches unity,AdS/CFT ratio is flat and many times smaller than pQCD

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

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

28. L k0 p k p Efficiency and acceptance corrected spectra original efficiency & acceptance relative corrected error

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. 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. 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) ? • 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 • Fragmentation is driven by fundamental formation time hadrons/ resonances partonic medium partonic medium hadrons/ resonances a mixed d.o.f. system

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

33. Quadrant correlation analysis: requires EMCal for jet reco and trigger side 1 near away side 2 near side1 away side2

34. Summary 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. Backup slides

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 medium properties through medium response • Can we measure a change in coupling and thus a change in the degrees of freedom ? • Can we measure chiral restoration ?

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 (<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

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. • Determine neutral energy in jet by measuring protons (neutrons) and K0s (for K0L) very precisely.

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. • Compare to models: • Recombination: L. Maiani et al. (hep-ph/0606217) • Quenched Fragmentation: Sapeta/Wiedemann (arXiv:0707.3494) • For resonances: • Possible chiral effects due to differing formation time for jet and bulk resonances. Determine statistics and resolution in quadrants (arXiv:0807.1509).