The Forward Vertex Upgrade Detector for PHENIX

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The Forward Vertex Upgrade Detector for PHENIX

• Sergey Butsyk
• for the PHENIX Collaboration

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Outline

• Muon Identification in PHENIX
• FVTX detector for Muon Arm Upgrade
• Displaced vertex muon tagging
• Signal to Background improvement
• Future Outlooks

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PHENIX Detector

• Muon measurements
• 1.2 lt h lt 2.4
• Two separate arms in forward and backward
  rapidity
• No vertex tracking
• All particles assumed to come from primary vertex
  measured by Beam-Beam Counter

Space for Vertex upgrade detectors
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Muon Sources in PHENIX
Muon ID
Absorber
Muon Tracker

• Muon arm consists of several layers of detectors
  and hadron absorbers
• Muon candidates consists of for
  current analysis
• Prompt muons Background
• Heavy flavor decay muons Signal
• Hadronic (p,K) decay muons Background
• Punch through hadrons Background

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Single Muon Analysis

• Analysis in pp and AuAu suffers from large
  hadronic background
• Strongly relies on hadron production yields and
  interaction cross sections for absorber material
• Need to improve background rejection capabilities
• No accurate vertex information, all particles
  assumes to come from primary vertex
• ? Propose to upgrade PHENIX muon arm with
  precision tracking detector

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FVTX Muon Arm Upgrade

• 4 discs of Si sensor in acceptance of each Muon
  Arm
• 75 mm pitch strips accurately measure R
  coordinate of track
• Scheduled to be installed in FY11

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FVTX Detector Elements

• 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

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Design Strategies

• Fitted track provides a DCA to the primary vertex
  (measured by central arm barrel VTX detector)

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DCA Performance

• Tracking uses Kalman fit to all the hits from
  FVTX and Muon Arm (also include VTX hits)

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DCA for Signal and Background

• DCA depends both on decay length and decay angle
• Hadron decays are easy to suppress due to large
  decay distance
• DCA in f already rejects a significant portion of
  hadronic background

hadrons
B
D
K
D decay
B decay
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Radial DCA and c2 cuts

• Adding FVTX hits into Muon arm help to remove
  hadronic decays between FVTX and MuTr
• c2/n for those tracks is a clear cut parameter

hadrons
D decay
D decay
B decay
hadrons
chi2

• Radial direction is much more precise for DCA
  measurement
• B and D meson decay muons produce asymmetric DCA
  distributions due to large decay angle
• Cut on negative DCAr improves S/B substantially

B decay
Cut region
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Heavy Quark S/B improvement

• Signal to background improves by a factor of 10
  over the whole range of measurements
• At the same time recover 20-30 after all the
  cuts
• Both statistical and systematic errors on Heavy
  Flavor signal improve due to the smaller
  background uncertainties contribution

x8 improvement
x3 improvement
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Heavy Flavor Signal Expectations

• Error bars show combined systematical and
  statistical error on Open Charm single muons
• Red Year2 pp results
• Blue Same data with FVTX detector background
  rejection

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Physics Outlook with FVTX

• Wide variety of physics probes can be measured
  with increased precision with FVTX detector
• Double spin asymmetry ALL
• Open Charm nuclear modification factor RAA
• J/y and y in pp and AuAu
• Muons from W decay

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Construction Schedule
pixels
stripixels
RD Phase
Construction Phase
Ready for Data

• Barrel VTX construction well underway
• pixel layers completion in 2009
• stripixels completion in 2010
• FVTX detector construction started in FY08,
  installation to be in 2011

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Conclusions

• FVTX detector upgrade significantly improves
  hadronic background rejection for all muon arm
  physics observables
• Tagging displaced vertexes of Heavy Flavor
  semi-leptonic decays with FVTX detector is a
  feasible task
• S/B for the Open Charm and Open Bottom single
  muons improves by a factor of 10 while leaving a
  large portion 20-30 of the signal after the cuts
• Detector is approved by DOE for construction
  (starting April 08) and planed to be put into
  operation in FY11