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Reconstruction tools for the study of short-lived

Reconstruction tools for the study of short-lived resonances in ALICE pp collisions at the LHC startup. F.Riggi Dept. of Physics and Astronomy and INFN, Catania. Outline. The ALICE experiment @LHC Short-lived resonances in ALICE pp collisions: preparing the tools for LHC startup

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Reconstruction tools for the study of short-lived

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  1. Reconstruction tools for the study of short-lived resonances in ALICE pp collisions at the LHC startup F.Riggi Dept. of Physics and Astronomy and INFN, Catania Outline • The ALICE experiment @LHC • Short-lived resonances in ALICE • pp collisions: preparing the tools for LHC startup • Results from local and distributed computing analysis ACAT 2007, Amsterdam, 23-27 April, 2007

  2. The Large Hadron Collider (LHC) @ CERN 4 major experiments waiting for the first beam… Z ALICE Detector @ Point2

  3. Point 2

  4. ALICE: A Large Ion Collider Experiment TOF TPC ITS

  5. ALICE will track and identify products from pp and nucleus-nucleus collisions in a large multiplicity environment Main tracking detectors: ITS and TPC PT > 1 GeV/c

  6. The silicon Inner Tracking System (ITS) Pixel (SPD) 9,830,400 channels Drift (SDD) 133,120 channels Strips (SSD) 2,608,128 channels

  7. Time Projection Chamber (TPC) Arrival of the TPC in the ALICE cavern

  8. Possible ALICE physics at the LHC startup (pp @0.9 TeV?) • Physics aspects • Compare pp and pp data at 900 GeV • Improve the precision in comparison with existing pp data at 900 GeV • Prepare the detector (calibration, alignment) • Provide a reference for data at different cm energies (2.4 TeV, 5.5 TeV?, 14 TeV). • Use first pp events to study global event properties: Charged Multiplicity, Pseudorapidity distributions, pT spectra • First strange particle studies • Short-lived resonances ?

  9. K f signal measured late decay p K p K* K rescattering signal lost p K* p kinetic freeze-out signal measured chemical freeze-out K K regeneration e+ signal measured early decay r e- p+ signal measured late decay r p- p r e+ signal measured late decay p e- Time Short-lived resonances have typical lifetimes comparable to that of the hot and dense matter created in AA collisions Observation of short-lived resonances is affected by two competing effects: rescattering vs regeneration • Resonance Life-time [fm/c] • r 1.3 • ++ 1.7 • f0(980) 2.6 • K*(892) 4.0 • S(1385) 5.7 • L(1520) 13 • ω(783) 23 • (1020) 45

  10. Study of short-life resonances in ALICE Main observables: ●Extraction of the signal/yields ● Mass and widths of resonances ● Transverse momentum and transverse mass spectra ● Particle ratios ● Elliptic flow ● Nuclear modification factors: RCP and RAA Resonance K*(892) Φ(1020)*(1520) Δ(1232) Decay channel (B.R.) K (~100%)K+K- (49%)N K (45%) Nπ (100%) Width [MeV/c2] 50.8 4.5 15.6 100 Life time [fm/c] 3.9 44 13 1.7

  11. pp collisions @900 GeV and @14 TeV ●LHC running scenario at startup: 1-2 days for physics collisions@900 GeV ? ●Expected no. of events: 0 to 106 ●To what extent is the study of short-lived resonances feasible? Results from: ● Local analysis via LSF (@900 GeV): 2 x 105 events ●Distributed GRID analysis (@14 TeV): 1.5 x 106 events Tuning of reconstruction tools: ●Study of the combinatorial background ●Perfect and realistic Particle IDentification Detailed examples for K*(892), other resonances treated in the same way

  12. Reconstruction of short-lived resonances requires optimal performance on: primary and secondary vertex reconstruction Efficiency 3D resolution σ~ 40 μm for pp σ~ 5 μm for PbPb An example of D0-> K-π+ decay in a large multiplicity environment

  13. Reconstruction of short-lived resonances requires optimal performance on: primary vertex reconstruction tracking efficiency ITS + TPC Kalman filter strategy allows a good tracking performance down to very low momenta Methods based on neural networks also implemented for stand-alone tracking in the ITS: 10% improvement

  14. Reconstruction of short-lived resonances requires optimal performance on: primary vertex reconstruction tracking efficiency momentum resolution pT resolution The inclusion of ITS, TPC and TRD results in pT resolution as good as 3 % up to 100 GeV/c

  15. Reconstruction of short-lived resonances requires optimal performance on: primary vertex reconstruction tracking efficiency momentum resolution track impact parameter Transverse impact parameter resolution Information on impact parameter mainly provided by the ITS

  16. Reconstruction of short-lived resonances requires optimal performance on: primary vertex reconstruction tracking efficiency momentum resolution track impact parameter particle identification r(s | i) Ci w(i | s)= Σk r(s | k) Ck Bayesian PID for each detector with ITS and TPC at low momenta… and TOF at high momenta…

  17. Signal extraction (unlike-sign) Inside same event, correlations between K+ and π- candidates K- and π+ candidates Evaluate invariant mass spectrum Example: K*(892)  Kπ (~100%) Mixed-event technique Combinatorial background Like-sign technique

  18. Transport of particles GEANT3 GEANT4 FLUKA Particle generation HIJING PYTHIA PDF Analysis HBT JET PWG0-4 ISAJET DPMJET HBTP Detectors TRD ITS HMPID EMCAL PHOS ZDC TOF TPC MUON T0 PMD V0 Response Alignment Geometry Calibration The AliROOT framework STEER Base classes, overall control AliReconstruction  ESD Reconstruction Event Summary Data

  19. Local analysis of 200,000 pp min bias events via LSF (Load Sharing Facility, A general purpose distributed computing system) For such application: ● Cluster of 60 multiprocessors CPU (up to 30 simultaneous jobs running) ● Generation and full reconstruction of events (1 job= 100 events) ● CPU time/event: 110 s @ 900 GeV ( 230 s @14 TeV) ● Total CPU time: approx. 200 days (about 10 effective days) Selection of primary and identified tracks Size reduction by 200 From generation and reconstruction AOD: Analysis Object Data ESD: Event Summary Data Kinematics Analysis Cuts,histograms,… …

  20. Effect of event selection (multiplicity and vertex location) on mixing procedure True background = (Signal) – (True pairs) (True Background) (Mixed events background) No event selection Only events with Δm<5 and Δzv < 3 cm mixed Selection in multiplicity is more effective than in primary vertex location

  21. Like-sign technique Signal Background

  22. Effect of particle identification on the results PID information from TPC and TOF used in the present analysis, with Bayesian procedure Different scenarios ● Perfect PID ● Realistic PID with no threshold on max_probability ● Realistic PID with improvement both in K and pion identification ● Realistic PID with improvement in K identification /no PID on pions K*(892) invariant mass with perfect PID

  23. Improving kaon identification in the Bayesian algorithm by a threshold on max.probability From max_prob > 0 to max_prob > 0.7

  24. Summary of PID influence on K*(892) reconstruction True Found Realistic PID Perfect PID S/B = 0.11 S/√B = 20.28 S/B = 0.111 S/√B = 20.01 No thresh on maxprob Maxprob > 0.7 (K) Maxprob > 0.7 (π) Maxprob > 0.7 (K) No PID (π)

  25. Similar analyses also done on other short-lived resonances Λ*(1520) Φ(1020) Particle ratios Statistical K*/K- 1.6 % Λ*/Λ 9 % Φ/K* 8 % Φ/Λ* 12 % K*/Λ* 9 % Yields and particle ratios uncertainties expected at 900 GeV with 200K pp events

  26. More detailed analyses require a large number of events Distributed analysis of 1.5 Mevents pp min bias events @ 14 TeV from PDC06 on the GRID via AliEn (ALICE Grid Environment)

  27. Submitting and monitoring jobs on the GRID via AliEn

  28. Distributed computing on the GRID: ~1.5 Mevents (pp @14 TeV) processed on the grid via AliEn middleware Monitoring the jobs on the GRID in ALICE

  29. Typical results at 14 TeV from distributed analysis on the GRID

  30. pT-analysis with realistic PID pT= 0 - 0.5 pT= 1.5 - 2 pT= 3.5 - 4

  31. Correction matrix pT=0-4 GeV/c (8 bins) Y = -1.5 – 1.5 (4 bins)

  32. Summary ● Study of short-lived resonances in pp and PbPb collisions @ LHC energies could be studied in ALICE from the very beginning ● With a small sample of events [O(105)] and realistic PID: ●Extraction of yields at least for K*(892), Φ(1020), Λ*(1520) ●Rough pT - distribution for K*(892) up to 1.5-2 GeV/c ●Particle ratios Φ/K*, Λ*/K*, Φ/Λ* measurable ● Analysis of O(106) pp events at 14 TeV fully reconstructed on the GRID ●Resonance yields with large statistics ●pT-analysis ● Correction matrix (y,pT) ● Extension to other resonances in progress

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