Silicon Vertex Detector Upgrade Physics Program

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Silicon Vertex Detector Upgrade Physics Program

• Patrick L. McGaughey
• P-25

July 17, 2003
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Physics Beyond Reach of PHENIX Baseline
Provide key measurements so far inaccessible at
PHENIX

• Detailed study of Heavy Quark production
• Beauty and Charm measurement in pp, p-A and A-A
  collisions.
• Energy loss of charm/beauty in hot matter.
• ?G (gluon polarization) measurement by heavy
  quark production over a wide Bjorken-x range.
• Gluon shadowing over a wide x range

• Measurements complement and enhance the present
  PHENIX physics program
• Fully exploit existing rare event capabilities
  of PHENIX
• Complete the PHENIX central and muon
  spectrometers

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Open Charm in Au-Au Collisions

• PHENIX measured charm via inclusive electrons
  (PRL88 (2002) 192303)
• Cannot distinguish between charm and beauty at pT
  gt 3 GeV/c
• Large systematic errors (50 of total cross
  section) due to background subtraction (dalitz
  decays and conversions), not shown on figure
  below

charm
beauty
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Direct Observation of Open Charm and Beauty
Detection of displaced decay vertex will allow
clean identification of charm and bottom decays

• Detection options
• Beauty and low pT charm through displaced e
  and/or m
• Beauty via displaced J/?
• Charm through D ? ? K

Central arm barrel VTX
muon arm endcap VTX
Need secondary vertex resolution lt 50 mm
(barrel), lt 150 mm (barrel)
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Silicon Vertex Tracker (VTX) in PHENIX
Strawman design under investigation
1.2lthlt2.4
hlt1.2
Pixel barrel (50 mm x 425 mm) Strip barrels
(80 mm x 3 cm) Endcap mini-strips (50 mm x 2 mm)
1.0 X0 per layer barrel resolution lt 50 mm
forward resolution lt 150 mm
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Silicon Vertex Upgrade
µ
D
IP
Channels Occupancy (central AuAu)
barrel 1st pixels 1.3 M lt1
barrel 2nd strips 92 K 12
barrel 3rd strips 123 K 7
barrel 4th strips 154 K 5
endcaps mini-strips 2.8 M lt3
Endcaps detect following by displaced vertex of
muons D -gt µ X B -gt µ X B -gt J/ ? X -gt
µ µ-
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Charm/Beauty measurements with the barrel VTX
Simulations

• Direct measurement of charmed hadron with
  central arm barrel

HIJING AuAu
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Simulated Signal to Noise for D-gt m with Endcap
VTX
300K per day with 10L0
Good S/N for pT gt 1 GeV/c
Events
pp ?S200 GeV ?L1036
pT GeV/c
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Simulation of B-gt J/y -gt mm- with Endcap VTX
1mm cut
Prompt J/y
?133?
1mm vertex cut eliminates gt99.95 of prompt J/y
Ratio of B decay to prompt J/y 1
Events
B decays
pp ?S200 GeV ?L1036
RHIC 10L0 400 B-gt J/y per day
Decay Distance (cm)
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Spin Physics with VTX Upgrade

• Measurement of gluon polarization by heavy flavor
  production
• using VTX measurement of displaced vertex
• Improved S/B (rejection of ? and K decays) ?
  higher sensitivity to DG(x)
• Much broader x-range coverage

via electrons
via muons
VTX significantly increases the Bjorken-x
converage of DG(x) measurement
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Measurement of gluon shadowing with VTX

• Heavy-flavor measurement in pA
• Single lepton and J/Y with displaced vertex
• Extracting gluon structure function in nuclei
  (shadowing)
• Vertex detector provides broader range in x in
  the predicted shadowing region (x lt 10-2)

via muons
via electrons
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Other Benefits of VTX upgrade to PHENIX muon
program
?, J/?, ? - VTX will improve mass resolution and
background rejection. ?, ?, ? VTX
can improve detection of these at rapidities
near zero. µ µ- Continuum - S/N can be
greatly improved by VTX. Charm,
beauty and Drell-Yan pairs can be
separated. e µ pairs VTX upgrade would improve
S/N of these charm decays.
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Summary

• Goal
• Detailed study of Heavy Quark production in p-p,
  p-A (d-A) and A-A collisions at RHIC.
• Physics with VTX upgrade
• Total charm and beauty cross sections, thermal
  charm
• Energy loss of charm and beauty in nuclear/quark
  matter
• Nuclear dependence (gluon shadowing) of charm and
  beauty production over a wide x range
• DG(x) measurement over wide x range (polarized
  proton)
• Proposed Silicon vertex detector
• Si barrel (1 pixel layer 3 strip layers)
• Si end caps (4 mini-strip layers)
• LDRD program underway (end of 2nd year)
• Very favorable review of VTX upgrade by RHIC DAC
  (fall 2002) and approval by PHENIX.
• Letter of Intent written (March 2003), encouraged
  by DOE to prepare Conceptual Design Report by end
  of CY 2003.