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Reconstruction, Charm, and Bottom with the ALICE EMCAL

Explore the physics motivation behind reconstructing charm and bottom quarks using the ALICE Electromagnetic Calorimeter at the Yale University Winter Workshop of Nuclear Dynamics in Big Sky, Montana in February 2007.

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Reconstruction, Charm, and Bottom with the ALICE EMCAL

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  1. Reconstruction Charm and Bottom with the ALICE EMCAL Mark Heinz for the ALICE collaboration Yale University Winter Workshop of Nuclear Dynamics Big Sky, Montana, Feb 2007

  2. Outline • Physics Motivation • Method for reconstructing Bottom via displaced vertices • ALICE Electromagnetic Calorimeter • EMCAL simulation status • Conclusion Winter Workshop, Feb 2007

  3. Physics Motivation • Current theoretical estimates for bottom and charm production still have large uncertainties. NLO pQCD, pp, s = 14 TeV CERN/LHCC 2005-014, hep-ph/0601164 MNR code: Mangano, Nason, Ridolfi, NPB373 (1992) 295. Winter Workshop, Feb 2007

  4. non phot. el. Physics Motivation STAR, submitted to PRL (nucl-ex/0607012) • Heavy ion collisions: • Interactions of heavy quarks with the medium • RHIC has recently shown the that the suppression of non-photonic electrons is not consistent with current energy loss predictions • Using the current best estimates for medium density (q-hat) the suppression pattern is consistent with charm quarks only up to 8 GeV/c in pT • Similar uncertainties are present for LHC energies Winter Workshop, Feb 2007

  5. Charm and Bottom via semi-leptonic decays • Semileptonic Channels: • c  e+ + anything (B.R.: 9.6%) • D0  e+ + anything(B.R.: 6.87%) • D e + anything(B.R.: 17.2%) • b  e+ + anything (B.R.: 10.9%) • B e + anything(B.R.: 10.2%)  single “non-photonic” electron continuum “Photonic” Single Electron Background: • g conversions (p0 gg) • p0, h, h’ Dalitz decays • r, f, … decays (negligible) • Ke3 decays (neglible) Winter Workshop, Feb 2007

  6. /e K CDF Phys.Rev.D66 (2002)) Signed DCA: Lxy= r .pe+k / |pe+k| Lxy Displaced Vertex Method • Search for semi-leptonic B-decay • B  e + D0  e + K- + +/e • Idea of Displaced vertex finding using muons was first tested at CDF • Create pairs of leptons and charged tracks which match the criteria for a secondary vertex: • pT> 2 GeV/c, R=2+2 Pe+K e- D0 SecVtx r Reminder: B ct: ~500 mm D ct: ~100 mm B- PrimVtx Winter Workshop, Feb 2007

  7. Efficiency of method improves significantly with #ITS hits Displaced Vertex Simulations (signal) • 1st Step: pure signal  efficiency • PYTHIA: 14 TeV, p+p, 40k events, pt(hard)>2.75 • Yields 6000 electrons within detector acceptance from beauty • Reconstruction efficiency per selected electron trigger ~70% Signal Lxy (cm) Winter Workshop, Feb 2007

  8. Charm PYTHIA events Displaced Vertex (charm backgrounds) • Dominant backgrounds are semi-leptonic charm decays • Simulation: PYTHIA, 14 TeV p+p, c-cbar, pt(hard)>2.1 GeV • Effective way of eliminating is by cut on invariant mass Winter Workshop, Feb 2007

  9. Displaced vertex (backgrounds) • 80k Minbias PYTHIA events (MSEL1) • Combinatoric, pi0 and photon backgrounds can be investigated • Background is consistent with zero, but more simulation statistics are needed to obtain an exact estimate of significance Minbias PYTHIA, 14 TeV Minbias PYTHIA, 14 TeV Winter Workshop, Feb 2007

  10. y track x vertex parametrized resolution Track impact parameter resolution • Primary vertex finding proceeds in 2 passes • Select primary tracks on the basis of their d0 • Cut |d0| < nsd0(pt) sd0(pt) = svtxstrack(pt) Winter Workshop, Feb 2007

  11. Secondary vertex resolution (simulation) /e • Determine position resolution for semi-leptonic heavy flavor vertices from PYTHIA • Position resolution in x,y,z is ~180mm, no strong dependency on coordinate K SecVtx reconstruced- MC (cm) reconstruced- MC (cm) reconstruced- MC (cm) Winter Workshop, Feb 2007

  12. Secondary vertex resolution (simulation) • Study of vertex resolution as a function of hits in the inner tracker ITS-hits, maximum of 6 hits. Winter Workshop, Feb 2007

  13. ALICE Set-up Size: 16 x 26 meters Weight: 10,000 tons TRD ITS TPC Winter Workshop, Feb 2007

  14. ALICE Electromagnetic Calorimeter Lead-scintillator sampling calorimeter Shashlik fiber geometry Avalanche photodiode readout Coverage: |h|<0.7, Df=110o Winter Workshop, Feb 2007

  15. 12 supermodules 24 strips in η 12 (or 6) modules in φ 12672 elementary sensors (towers) 77 alternating layers of 1.44 mm Pb (1% Sb) 1.76 mm polystirene scintillator Dh x Df = 0.014x0.014 ALICE EMCAL (2) Supermodule Module (2x2 towers) Winter Workshop, Feb 2007

  16. EMCAL energy resolution • Energy resolution has been measured and is within specifications ~12%/E +2% Production Module Spec Prototype Module Spec Winter Workshop, Feb 2007

  17. EMCAL Project milestones • 18 institutions worldwide of which 13 are from ALICE-USA collaboration • Assembly of supermodules will be shared between Yale (US) and Grenoble (F) • US-portion of project dependant on funding from DOE: CD-2 (critical decision) this summer. • Assembly and testing of supermodules (SM) at Yale to start in 2008 • Installation of first SM in ~2009 (low luminosity PbPb) Winter Workshop, Feb 2007

  18. EMCAL software development • Cluster shape analysis for PID • Electron/Hadron discrimination • Track-Cluster Matching • Electron trigger simulations • High-Pt simulations (jet-finder) Institutes involved in HF simulations: Yale, LBL, LLNL, WSU, Nantes (Subatech), Strassbourg, Catania Winter Workshop, Feb 2007

  19. Cluster in EMCAL  ° hadrons Study by Guenole Bourdaud EMCAL PID • e/p discrimination • p/E distribution • g/p0 discrimination • Cluster shape analysis • Effective mass Winter Workshop, Feb 2007

  20. Hadron/p0 discrimination • Granularity study of EMCAL Granularity 2x2 Granularity 3x3 For a 30 GeV photon the 0 suppression factor improve from 10 to 100 when increasing the granularity from 2x2 to 3x3 Study by A.Pavlinov (WSU) Winter Workshop, Feb 2007

  21. dN/dη = 4000 TPC track to EMCAL cluster matching • Code is now in Alice CVS • Good matching effiency for low multiplicity • Still some parameter tuning needed for Hijing simulations Cluster Matching Prob for electrons % Mult = 10 % Study by A.Pulvirenti (Catania) Winter Workshop, Feb 2007

  22. Conclusion • Displaced vertex method will be promising in measuring direct B-meson contribution to non-photonic electrons • The method combines the EMCAL PID and triggering capabilities • The ALICE EMCAL project is a collaboration between ALICE USA and European institutions • The simulations for the EMCAL are on track, however more detailed physics simulations are required for the DOE CD-2 decision this summer Winter Workshop, Feb 2007

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