Reconstruction Charm and Bottom with the ALICE EMCAL

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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

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Outline

• Physics Motivation
• Method for reconstructing Bottom via displaced
  vertices
• ALICE Electromagnetic Calorimeter
• EMCAL simulation status
• Conclusion

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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.
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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

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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)

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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
• pTgt 2 GeV/c, R???2??2

PeK
e-
D0
SecVtx
r
Reminder B ct 500 mm D ct 100 mm
B-
PrimVtx
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Displaced Vertex Simulations (signal)

• 1st Step pure signal ? efficiency
• PYTHIA 14 TeV, pp, 40k events, pt(hard)gt2.75
• Yields 6000 electrons within detector acceptance
  from beauty
• Reconstruction efficiency per selected electron
  trigger 70

Signal
Lxy (cm)
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Displaced Vertex (charm backgrounds)

• Dominant backgrounds are semi-leptonic charm
  decays
• Simulation PYTHIA, 14 TeV pp, c-cbar,
  pt(hard)gt2.1 GeV
• Effective way of eliminating is by cut on
  invariant mass

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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
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Track impact parameter resolution

• Primary vertex finding proceeds in 2 passes
• Select primary tracks on the basis of their d0
• Cut d0 lt n?sd0(pt)
• sd0(pt) svtx ? strack(pt)

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Secondary vertex resolution (simulation)

• Determine position resolution for semi-leptonic
  heavy flavor vertices from PYTHIA
• Position resolution in x,y,z is 180mm, no strong
  dependency on coordinate

?/e
K
SecVtx
reconstruced- MC (cm)
reconstruced- MC (cm)
reconstruced- MC (cm)
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Secondary vertex resolution (simulation)

• Study of vertex resolution as a function of hits
  in the inner tracker ITS-hits, maximum of 6 hits.

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ALICE Set-up
Size 16 x 26 meters Weight 10,000 tons
TRD
ITS
TPC
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ALICE Electromagnetic Calorimeter
Lead-scintillator sampling calorimeter Shashlik
fiber geometry Avalanche photodiode readout
Coverage hlt0.7, Df110o
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ALICE EMCAL (2)
Supermodule

• 12 supermodules
• 24 strips in ?
• 12 (or 6) modules in f
• 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

Module (2x2 towers)
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EMCAL energy resolution

• Energy resolution has been measured and is within
  specifications 12/?E 2

Production Module Spec
Prototype Module Spec
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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)

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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

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EMCAL PID

• e/p? discrimination
• p/E distribution
• g/p0 discrimination
• Cluster shape analysis
• Effective mass

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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)
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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)
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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