1 / 15

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

tadhg
Download Presentation

Perspective on Electron-Tagging in ALICE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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)

More Related