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Perspective on Electron-Tagging in ALICE

Perspective on Electron-Tagging in ALICE. Mark Heinz, Josh Spitz (grad student) Yale University ALICE-USA collaboration meeting Oct 7, 2006. Why measure Beauty with electrons?. Semi-leptonic decay channel of heavy flavor is large

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Perspective on Electron-Tagging in ALICE

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  1. Perspective on Electron-Tagging in ALICE Mark Heinz, Josh Spitz (grad student) Yale University ALICE-USA collaboration meeting Oct 7, 2006

  2. Why measure Beauty with electrons? • Semi-leptonic decay channel of heavy flavor is large • EMCAL provides signal enhancement through triggering capabilities for electrons • Solve theoretical uncertainties of HF models (NLO pQCD) • Investigating B-Fragmentation function in vacuum and (more importantly) in the dense QGP medium ALICE collaboration meeting (Oct 6-7,2006)

  3. Methods of measuring Beauty ? • Beauty is measured through it’s semi-leptonic channel: • Secondary Vertex reconstruction method • Relies on e/h discrimination and resolution of sec. vertex position (get’s better with pT) • Impact parameter method (Padua) • Relies on e/h discrimination and resolution of electron impact parameter (get’s worse with pT) • Di-Muon reconstruction • N-Prong vertex method (no PID) • … ALICE collaboration meeting (Oct 6-7,2006)

  4. K Pe e- D0 SecVtx r B- Method: Secondary vertex reconstruction • Search for semi-leptonic B-decay • B  e + D0  e + K- + + • Create pairs of leptons and charged tracks which match the criteria for a secondary vertex: • pT>1 GeV/c, R=2+2 • Idea of displaced vertex finding was first used by CDF using muon-hadron pairs • Critical Detectors: EMCAL, ITS(SVT), TPC Quantity sDCA: L(xy)z= r .pe / |pe| STAR Simulation + SVT: B-meson in empty events m+h pairs Lxy (mm) Lxyz (cm) ALICE collaboration meeting (Oct 6-7,2006) CDF, Phys Rev D 66 (2002)

  5. STAR Simulation of B-Signal from secondary vertex method • PYTHIA generated with and without SVT: • Example: B  e- + D0  e- + K- + + • Kinematics: MSEL 5 (bottom) • Propagate through GEANT +TPC slow and SVT Fast simulator (80m resolution) – has a i.p. resolution ~ 150-200 mm • Primary Vertex “smeared” around (0,0,0) with 150m resolution in each (x,y) and z. How can the SVT (Silicon Vertex Tracker) help? STAR simulation TPC+SVT ~600um STAR simulation TPC ~2000um • Resolution of e-h-DCA • at Secondary Vertex • Critical for calculating sDCA • Critical for combinatorical • background rejection ALICE collaboration meeting (Oct 6-7,2006) electron-hadron DCA @ sec. vertex

  6. Semi-leptonic D0 (~120mm) Semi-leptonic B0 (~500mm) Disentangling Beauty/charm sec. vertices • Main background will be charm semi-leptonic decays. PYTHIA Simulation Inv mass e + h (K) PYTHIA Simulation PYTHIA Simulation • Can be cleanly seperated by applying invariant mass cut ALICE collaboration meeting (Oct 6-7,2006)

  7. Momentum dependence of B-meson Signal • Efficiency for B-Signal from sec. vertex method per selected electron for the integrated pT-spectrum is: ~4% • This value depends strongly on the spectrum of the B and on the cuts to reject combinatorical background • At least a factor 2 efficiency improvement is achieved at higher pT Cuts are different than below This is in contrast to the IP-method (Padua) of measuring B-mesons where the stat. errors increase significantly with pT ALICE collaboration meeting (Oct 6-7,2006)

  8. “Plan of Attack” for Alice • Complete simulations of semi-leptonic B-Signal (PYTHIA) using sec. vertex method • Study electron ID in EMCAL, ie. analyze cluster shapes and energy deposition • Reduction of hadronic backgrounds • Simulation of backgrounds in sec. vertex method and optimization of cuts. • Performance of ITS for electrons. Necessary resolution for Sec Vtx method. ALICE collaboration meeting (Oct 6-7,2006)

  9. First simulation results (EMCAL) • Electron/Hadron discrimination: p/e plots for different MC particles, determine energy resolution • Electron/Gamma discrimination: Track-Veto method… • lot of work done by Gustavo (PHOS) • has to be repeated for EMCAL pT> 2GeV Hadrons gamma Pions electrons p/E p/E ALICE collaboration meeting (Oct 6-7,2006)

  10. Prim tracks First simulation results (ITS) • Minbias Pythia simulations (only 140k events) • ITS Hit probabilities are different for pions and electrons…needs further investigation • Improvement in track i.p. by adding ITS hits. All tracks i.p. [cm] Hadrons Pions electrons N(ITS hits) ALICE collaboration meeting (Oct 6-7,2006)

  11. To-Do List for HF-simulation • Study cluster shapes, ie. size (digits per cluster) and dispersion as a function of particle species. • Track-Cluster Matching (code development in progress at Catania) is starting point • Study reconstruction efficiencies for electrons and hadrons ALICE collaboration meeting (Oct 6-7,2006)

  12. Summary • STAR is focusing on Heavy flavor measurement with SVT in Run 7 (2007) • In ALICE we should be able to do a “much better” job, considering the improved impact parameter resolution and the enhanced HF yields • ALICE semi-leptonic heavy flavor simulation studies have now started at Yale: • We will be focusing on electron-ID in EMCAL • Efficiency of Sec. Vertex Beauty reconstruction method • Estimate backgrounds for the sec. vertex method ALICE collaboration meeting (Oct 6-7,2006)

  13. backups

  14. Impact parameter vs PID nITS=0 nITS=4 nITS=5 nITS=6 Electron Hadron pion ALICE collaboration meeting (Oct 6-7,2006)

  15. e from c e from b d0 [cm] ALICE method: impact parameter • Simply use impact parameter of all identified electrons above 1 GeV/c • Electrons from Beauty can be identified in a “sweetspot” of d0 ~200-500 mm (red shaded area) • In STAR, even with optimistic resolution parameters we are not able to obtain such an area in d0 STAR MonteCarlo (H.Caines) ALICE (PPR, Lunardon) Pure MC SVT (resolution variable) TPC only d0 [cm] ALICE collaboration meeting (Oct 6-7,2006)

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