Measuring Charm and Bottom using the PHENIX Silicon Vertex Detectors

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Measuring Charm and Bottom using the PHENIX
Silicon Vertex Detectors

• Hubert van Hecke,
• Los Alamos National Laboratory
• for the PHENIX collaboration

Outline

• Physics goals
• Detector requirements
• Description of the detectors
• Some MC results
• Construction Timeline

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Physics Goals for the Silicon Vertex Detectors
e-

• Study production and flow
• mechanisms of heavy quarks
• Study of production and
• suppression of quarkonia
• Measure reaction plane
• Improve p resolution
• Improve high-pT tracking
• q, g contribution to proton spin

m

• Signal channels
• b-gtB-gt??e
• c-gtD-gt ??e
• J/?, ?-gt ?? ???,ee-
• hadrons

e
m-
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Separate Signal from Backgrounds

• The problem backgrounds (? -gtm?e and K-gt m?e)
  overwhelm the signal

Solution Mean ?,K -gtm?e decay distance is
large D, B mesons travel some distance before
semileptonic decay to muons or electrons Prompt
m?e have 0 DCA By measuring the DCA to the
primary vertex, we can separate D, B decays from
prompt leptons and from long-lived decays from ?,
K
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Detector Specifications

• We require
• DCA resolution lt 50 um for the central barrel
• lt 100 um for the
  forward detectors
• Occupancy lt 10
• Large solid angle coverage
• ?? lt 1.2 - barrel, standalone
• ?? lt 0.35 - barrel, matches central arms
• 1.2 lt ?? lt2.4 - forward detectors, covers
  most of
• the muon arms
• Capability to match tracks with Central arm and
• Muon arm tracking systems
• Enough hits (gt3) to reconstruct a track
• Minimal mass

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Detectors
80 cm
40 cm
38 cm

• .

Forward vertex detectors (FVTX)
Barrel vertex detector (VTX)
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Barrel Inner 2 Pixel Layers

• Inner 2 layers
• pixels 50 x 425 ?m
• 200 ?m - thick Silicon
• R 2.5, 5.0 cm
• Length 22 cm
• 1.3, 2.6M channels
• Readout with ALICE1LHCb chip
• Bump-bonded to detector
• RL 1.44 total
• AuAu occupancy 0.5, 0.2

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Barrel Inner 2 Pixel Layers (contd)
Test of half-ladder, extension cable, spiro
board successfully completed
Carbon support cooling tube prototype
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Barrel Outer 2 Layers

• Outer 2 layers stripixels
• elements 80 x 1000 ?m
• 650 ?m - thick Silicon
• R10,14 cm
• Length32, 38 cm
• 140K, 280K channels
• Readout with SVX4 chip
• RL 2.7 total
• AuAu occupancy 4.6, 2.6

Single_sided, 2D readout
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Barrel - strip layers (contd)
Strip pixel sensor wafer made by HPK
ROC-3 prototype currently under study
CFC
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Forward Detectors
Basic unit wedge

• 4 disks / side
• 48 wedges/disk
• 75 um strips,
• 2.8-11.2 mm long
• 1664 strips/column
• 1.1M channels total
• readout with FPHX chip,
• derived from BTeV chip.
• RL 2.4

2.8 - 11.2mm strips, 75 um wide



12.5 cm 1664 strips 13 chips
75-um strips
3.750
2.8mm strip
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Forward detectors (contd)
Mechanical design 80 done
Electronics chain fully prototyped
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• Some simulation results

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Barrel Expected DCA resolution
Hadron background
s 40 mm
DCA distribution for single pions in 3ltpTlt4
GeV/c. Simulation is done with 200 micron pixel
layers and 650 micron strip layer. The passive
material is 1.0 per pixel layer and 2.75 per
strip layer.

• Results of simulation of AuAu collision.
• After a chi2 cut, DCA distributions of light
  hadrons and D0 decay are clearly separated

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Endcaps Open charm, bottom signal

• In the forward detectors
• Using DCA cuts, plus ?? and isolation cuts, we
  can now improve the signal/background for D,B-gt?

D- -gt??
B- -gt??
S/N
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Improved resolution background reduction
?

• Simulated RHIC-II pp run
• - improved background . rejection
• - improved mass resolution
• - separate ????

Without FVTX
??
?
With FVTX
?
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Status and outlook
- Barrel construction well underway
pixel layers completed in 2009, installed and
ready for PHENIX run 10 stripixels
completion 2010, insalled and ready for run 11
- Forward detector construction started in FY08,
installation in 2011, ready for run 12

• Collaborating institutions
• KEK, RIKEN, Rikkyo, Ecole Polytechnique, Columbia
  U. SUNY Stony Brook, Los Alamos, Brookhaven, Oak
  Ridge U. New Mexico, New Mexico State U. Iowa
  State U. Bhabha Atomic Research Centre, India
  Saclay, France Charles University, Prague Czech
  Technical University, Prague Institute of
  Physics, Academy of Sciences, Prague Kyoto
  University University of Jyvaskyla, Finland
  Yonsei University, Korea

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.

• backups

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Endcaps DCA resolutions
100 ?m

• Since the barrel pixels are // to the beampipe
  (orthogonal to the FVTX mini-strips), using them
  greatly improves phi resolution

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External mount
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Acceptance

• Since the event vertex spans
• -10 cm in z, we can use the barrel hits for
  some events.

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Can we match muon arm tracks with a FVTX track?

• Use the chi2 of the Kalman track fitter

3 GeV muon 75 correct match
9 GeV muons 93 correct match