Matching between charged tracks and electromagnetic calorimeter (EMCAL) clusters in ALICE

1. Matching between charged tracks and electromagnetic calorimeter (EMCAL) clusters in ALICE Alberto Pulvirenti University & INFN Catania ACAT 2007 Conference Amsterdam, 24 April 2007

2. Outlook • The context • the ALICE experiment • the EMCAL detector • the computing framework • The algorithm ingredients • ALICE tracking • EMCAL clusters • Description of the algorithm • Tests and results • Conclusions and perspectives

3. http://www.cern.ch LHC ~9 km SPS CERN The CERN Large Hadron Collider & ALICE

4. Pb-Pb collisions at 5.5 A TeV Expected charged multiplicity from RHIC data: (dNch / dy)y=0 = 3000 design baseline: (dNch / dy)y=0 = 8000 Luminosity for Pb-Pb: Lmax = 11027 cm-2s-1 Event rate: 8000 minimum bias coll. / s ~109 events/year 1% collected Some numbers about LHC “worst” actual case: RHIC …and “worst” expectation for LHC

5. The ALICE detector HMPID PID at high pt EMCAL Photons, jets TOF PID TRD Electron ID PMD g multiplicity TPC Tracking, dE/dx MUON-Arm m-pairs ITS low pt tracking Vertexing PHOS g,p0

6. Particle transport GEANT3 GEANT4 FLUKA Particle generators HIJING PYTHIA PDF Analysis HBT JET PWG0-4 ISAJET DPMJET HBTP AliROOT: the ALICE computing framework STEER Base classes, overal control AliReconstruction  ESD reconstruction Event Summary Data Detectors TRD ITS HMPID EMCAL PHOS ZDC TOF TPC MUON T0 PMD V0 Response Alignment Geometry Calibration

7. The ElectroMagnetic CALorimeter (EMCAL) Acceptance Dh = 1.4 DF = 100o

8. 12 supermodules 24 strips in η 12 (or 6) modules in φ projective wr. to TPC/TRD sectors 12672 elementary sensors (towers) 77 alternating layers of 1.44 mm Pb (1% Sb) 1.76 mm polystirene scintillator radiation length: ~20 X0 Acceptance: φ : 80  190 degrees η : -0.7  0.7 The ElectroMagnetic CALorimeter (EMCAL)

9. EMCAL primary objective: jet study • High energy partons fragmentation jets • Jets traveling through a dense color medium loose energy through gluon radiation  “jet quenching” EMCAL PROVIDES: • Jet trigger • Improved jet reconstruction up to 200 GeV jets • background reduction • improved energy resolution (including neutrals)

10. PID with EMCAL (high momentum particles) • g/p0 discrimination (measure of direct photons) • invariant mass • shower shape analysis • e/p discrimination • E (from EMCAL) / p (from tracking) ratio

11. Tracking in ALICE TIME PROJECTION CHAMBER (TPC) up to 180 pt / track [main contribution - seed] INNER TRACKING SYSTEM (ITS) up to 6 pt / track [resolution improvement] TRANSITION RADIATION DETECTOR (TRD) up to 6 pt / track • Tracking procedure based on Kalman Filter: • Predict track intersection point at a layer of tracking device • Choose the cluster which determines the smalles ² increase • Add a cluster  adjust track parameters according to Kalman matrix equations

12. ALICE tracking work flow time ITS TPC TRD Seeding & inward track propagation through the TPC Inward track propagation through the ITS Outward track propagation through the ITS Outward track propagation through the TPC Outward track propagation through the TRD Final inward re-fit through all tracking devices, up to the beam pipe

13. Barrel to EMCAL track matching Target: • associating to each track the EMCAL cluster generated by its particle (if any) • cleaning the sample of cluster for photon analysis (jets) • adding PID information from EMCAL to high momentum charged tracks Implementation in AliROOT framework • “tracker” class  algorithm execution • “track class”  input data  final information • EMCAL clusters are not used to update the track state vector

14. Work-flow of the algorithm Propagate track to the EMCAL surface Geometrical CUTS Search for EMC clusters close to the intersection Quality parameter: Track-Cluster distance Create a list of “match candidates” Save the “surviving” candidates as final information. Each cluster/track is used only in the “best” candidate

15. Performance tests Test on single-track events • Data: • 1 track / event (fixed type) • fixed momentum • 1, 5, 10, 25, 50, 75, 100 GeV • fixed direction • Objective: • evaluate / shift between track hit and reconstructed cluster • evaluate typical cluster size (# towers) Test on “box” events • Data: • <N> (fixed) track / event • photons, pions, electrons • Random momentum in a fixed range (1-10 GeV) • Random direction in a fixed window (EMCAL acceptance) • Objective: • evaluate efficiency and contamination in a simple multi-track scenario Test on “physical” simulations Proton-Proton collision:PYTHIA Pb-Pb collisions:HIJING parameterized • Objective: • evaluate efficiency and contamination in a “physical” sample with a realistic momentum distribution and signals from neutral particles (as a perturbation factor)

16. Phi and Eta shift between hits and clusters ELECTRONS PHOTONS PIONS

17. Average #digits per particle amp > 2% of total amp > 1% of total amp > 5% of total amp > 10% of total

18. Cluster/Particle energy comparison electrons & photons: ~100% of total pions: ~20% of total

19. Efficiency Contamination Track matching evaluation Geometrical cuts tuned on pion events and used for all tests without changes

20. Efficiency evaluation: “box” of electrons 10 primaries / event 50 primaries / event 100 primaries / event 150 primaries / event

21. Efficiency evaluation: “box” of pions 10 primaries / event 50 primaries / event 100 primaries / event 150 primaries / event

22. Efficiency evaluation: PYTHIA simulation of minimum bias p-p collisions at 14 TeV

23. Efficiency evaluation: HIJING parameterized (preliminary) dN/dη = 4000

24. Conclusions & perspectives • Track matching code preliminary version implemented within ALICE reconstruction framework • based on Kalman Filter-style track propagation • Efficiency results: • box: good • not negligible contamination for high multiplicity (150) • PYTHIA: good • HIJING: good only for very high momenta • investigate performances at this track density • Future perspectives: • improve results for high mutiplicity events • cluster pattern study

26. Seed: outer “snapshot” of the reconstructed track Propagate tracks to the EMCAL surface Work-flow of the algorithm:STEP 1  propagation XY plane (transverse to beam) Cluster positions Track intersections with EMCAL

27. Track propagation plane(in track local coords.) Track local reference system: rotation of detector plane around Z axis, in order to put it in a plane orthogonal to X axis X = distance of detector plane from origin Y X Z not all clusters lie in the same plane (Δy,Δz)LOCAL cuts  (Δφ,Δη)GLOBAL cuts

28. Insertion of track matching into global barrel reconstruction work-flow EMCAL (matching) TOF (matching) Entry point TRD (out) TRD (refit) TPC (out) TPC (in - I) TPC (refit) ITS (in – I) ITS (out) ITS (refit)

29. Energy distribution in clusters Portion (%) of total cluster energy per hit tower. p (25 GeV) e (25 GeV) LOG scale!!!

30. Heavy ion collisions in a new energy range Properties of nuclear matter at high temperature and energy density Formation and study of Quark-Gluon Plasma (QGP) ALICE objectives QGPNucleons Nuclei Atoms Today Big Bang 10 –6 s 10 –4 s 3 m ~1010 yrs