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Heavy flavor measurements with high- p T electrons in the ALICE EMCal

Heavy flavor measurements with high- p T electrons in the ALICE EMCal. Mark Heinz (for the ALICE Collaboration) Yale University 26 th Winter Workshop on Nuclear Dynamics Ocho Rios, Jamaica, Jan 2-9 2010. Physics Motivation ( p+p ). Beauty physics in p+p (examples):

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Heavy flavor measurements with high- p T electrons in the ALICE EMCal

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  1. Heavy flavor measurements with high-pT electrons in the ALICE EMCal Mark Heinz (for the ALICE Collaboration) Yale University 26th Winter Workshop on Nuclear Dynamics Ocho Rios, Jamaica, Jan 2-9 2010

  2. Physics Motivation (p+p) • Beauty physics in p+p (examples): • Transverse momentum spectrum, X-section, (normalization for “Quarkonia” studies) • Jet-Shapes • Fragmentation function Jet-Shape X-section vs NLO Y(r/R) CDF (PRD78,2008) Winter Workshop 2010, Jamaica

  3. Physics Motivation (Heavy Ion) • Investigate energy loss of quarks vs. gluons • Investigate differences between the predictions of pQCDvs ADS/CFT RHIC (200 GeV) RAA(charm)/RAA(beauty) pQCD ADS/CFT Horowitz, Gyulassy (arXiv:0804.4330) S.Wicks et al (Nucl.Phys.A784 (2007) Winter Workshop 2010, Jamaica

  4. Electron Identification in Alice • Barrel (TPC/TRD/TOF) • Superior electron/hadron discrimination up to p~10 GeV/c • EMCal • Very good electron/hadron discrimination for p > 10 GeV/c. PID parameters tuned. • 4 Super-modules installed in ALICE • 5th SM at calibration stage at Yale University • Energy calibration of detector with p0 currently underway • Part of routine data-taking • Sufficient coverage for day 1 physics Run 2010 configuration (Pb+Pb low luminosity) Winter Workshop 2010, Jamaica

  5. Electron Rates (PYTHIA) • PYTHIA Rates are scaled to 1 month of Pb+Pb running (0.5mb-1s-1, 106sec, A2) • Significant beauty-electron yield out to pT~50 GeV/c • Dominant background are W-electrons above 20 GeV/c • Hadron/Electron ratio is 500-800. Sets scale for PID performance. Winter Workshop 2010, Jamaica

  6. EMCAL PID: E/p • For electron identification we use the ratio of Ecluster/ptrack. • Track-Cluster matching efficiency ~65% • The electron peak can be cleanly separated from pions. Material interaction in front of the EMCAL does deteriorate the performance. Simulation Simulation Winter Workshop 2010, Jamaica

  7. Hadron Rejection Power (HRP) From published NIM paper arXiv: 0912.2005 • Results from CERN test-beam for energies 40-80 GeV. These compare well to ideal simulation (ie. no additional detector material in front of EMCAL) • Results from simulation for a set of optimized cuts for electron identification and full ALICE detector simulation. For ~65% electron efficiency we obtain a HRP between 400-1000. Simulation Winter Workshop 2010, Jamaica

  8. Electron Spectra • Reconstructed conversion electron vertices are found by the V0-finder and tagged using an invariant mass cut (Minv<100 MeV). These are then subtracted from the inclusive electrons. • After EMCAL PID non-photonic electron candidates dominate misidentified hadrons by at least factor 10. • Dominant background to b-electrons above 20 GeV/c from W-electrons. This can be further reduced by secondary vertex strategies. PYTHIA Winter Workshop 2010, Jamaica

  9. Corrected Spectra • Efficiency corrected rates of non-photonic electron candidates • Systematical errors indicate the variation of EMCAL PID criteria PYTHIA Simulation Winter Workshop 2010, Jamaica

  10. /e K Pe+K e- CDF Phys.Rev.D66 (2002)) D0 SecVtx r B- PrimVtx Lxy B-Tagging: Displaced Vertex Method • The method previously used by CDF to identify secondary vertices from semi-leptonicdecays. Further development and implementation in ALICE. • Breakdown of method: • Find a high-pt electron trigger particle in EMCAL • Pair with all charged hadrons within a cone of radius dR. • Reconstruct “approximate” (average between B-D decay) secondary vertex using an identified electron and all associated hadrons • apply more cuts to reduce backgrounds from other leptonic decays. • Plot Lxy distribution and obtain B-contribution from positive/negative imbalance Lxy= r .pe+k / |pe+k| M.Heinz, arXiv: 0712.2422 Winter Workshop 2010, Jamaica

  11. Method Cuts • Tracks • Track Impact Parameter < 0.5 cm (electron) • Silicon Hits: ITS>=4 • PT > 1.0 GeV/c (associated hadrons) • Secondary Vertex • pairDCA< 0.02 cm • R= √Dh2+Df2 (electron-hadron) < 1.0 rad • Vertex length < 1.0 cm • SignDCALxy > 0.1 • Invariant Mass (e+k) > 1.5 Winter Workshop 2010, Jamaica

  12. Sign-DcaLxy • The method relies on the fact that the B-meson creates a displaced vertex with ct~500mm. Winter Workshop 2010, Jamaica

  13. Electron tag efficiency • Tagging algorithm can be tuned by requiring a given number of heavy flavor vertices which pass our cuts Winter Workshop 2010, Jamaica

  14. B-Jet Tagging performance in p+p • FASTJET Jet-Finding Algorithm: kT, R= 0.4 (anti-kT comparable) • Standard definitions: • Efficiency = tagged B-jets/MC-B-jets • Fake Rejection = Non B-Jet efficiency • Algorithm currently tuned for maximum fake rejection. Studies ongoing to map out full cut-space • Results comparable to CMS Soft Lepton Tag (Note 2005/058) Signal Efficiency Fake rejection PYTHIA jets (pThard 12-150 GeV/c) PYTHIA jets (pThard 12-150 GeV/c) Winter Workshop 2010, Jamaica

  15. Expected tagged Jet yield Winter Workshop 2010, Jamaica

  16. Conclusions & Outlook Conclusions • EMCAL PID (using E/p method) works well and we expect a hadron rejection powerof 400-1000 (65% efficiency) for 10 GeV/c< pT <80 GeV/c. Hadron/Electron ratios from MC in this range are ~500. • Reconstructed electrons after subtraction of the photonic component and EMCAL PID dominate the background of mis-identified hadrons by at least a factor 10. • Preliminary studies of B-jet tagging algorithms in simulated p+p events have been performed. First results for efficiency and fake rejection using the displaced vertex method have been calculated and are comparable to similar methods used in other experiments. • Tagged Jet-yieldsshould besufficient for measurements of B-jets to pT~50-60 GeV/c. Outlook • More optimization of B-tagging algorithms • First look at real data … Winter Workshop 2010, Jamaica

  17. Backup

  18. CMS Electron Tag performance • c • uds • g - Winter Workshop 2010, Jamaica

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