H. Wieman

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EIC Vertexing for A A

• H. Wieman
• Sept. 19, 2002
• BNL

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Motivation for an inner tracker

• A tool for reducing combinatory background to
  measure yields of particles with short decay
  times
• Works with collections of many events
• Background can be less than 1 per event, but
  signal is still less
• Does not extract special decays event by event in
  the high multiplicity environment of AA
• Measure D mesons

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Invariant mass reconstruction of D0s ?k
?(preliminary simulation)
D0
S
B
M (GeV)
Because AA at RHIC produces very high
multiplicity events the vertex detector must be
exceptionally good to reduce B
Number of events required to get a statistically
significant result
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1 priority go thin to reduce Background
Shows effects of first layer SI thickness,
includes contribution from 760 ?m beam pipe.
Preliminary GEANT simulation
B
Si thickness reduction 300 ?m ? 50 ?m reduces
beam time by factor 19
Si thickness (?m)
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The options

• ATLAS style hybrid
• Thick 300 ?m Si
• High power 800 ?W/cm2 requires liquid cooling,
  more thickness
• CCDs
• Very thin
• Power vs speed ?
• Rad soft
• Active Pixel Sensors (APS)
• Very thin
• Rad hard enough
• Slow? But good potential with low power
• New technology with normal uncertainties

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APS Compromises

• Short, does not cover diamond
• Most running not luminosity limited so not an
  issue unless run with a very good trigger
• Slow, contains multiple events
• Background rejection is pileup tolerant

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False rejection by pileup

• Purpose of vertex detector remove primary
  tracks before calculating invariant mass
• 40 x design luminosity, 5 ms readout
• 400 hits/cm2
• 1.4 pixels filled
• false rejection 0.5
• 40 X design luminosity, 20 ms readout
• 1500 hits/cm2
• 5.3 pixels filled
• false rejection 2.9

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A Monolithic Active Pixel Sensor for Charged
Particle Tracking and Imaging using Standard VLSI
CMOS TechnologyJ.D. Berst, B.Casadei, G.Claus,
C.Colledani, W.Dulinski, Y.Hu, D.Husson, J.P.Le
Normand, R. Turchetta and J.L.RiesterLEPSI,
StrasbourgG.Deptuch, Y.Gornushkin, S.Higueret,
M.WinterIReS, Strasbourg

• LEPSI - IReS APS
• 20 ?m square pixels
• 4 64X64 arrays
• MIMOSA 1, 0.6 ?m CMOS
• MIMOSA 2, 0.35 ?m CMOS

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All this on a 23 ?m by 23 ?m pixel
Rapid progress toward fast low power readout with
on detector zero suppression
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LBL APS test with 1.5 GeV/c e-beam
17 e RMS per pixel
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LBL APS measured MIP signal
Sums of 25 pixel regions centered on pixels with
ADC ? 7
Same sums with empty frames
Background subtracted APS signal with Bichsel
calculation for 8 mm Si

• Conclusion, signal to noise is good enough to get
  good efficiency without excessive false hits
• The above analysis is with CDS and leakage
  current subtraction

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Active Pixel Sensor (APS)

• 20 ?m square pixels
• 5 chips per slat
• 90 million pixels
• 50 ?m thick chips
• 760 ?m Be beam pipe

5.6 cm
8 cm
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One of 8 Modules
LBNL mechanical concept for an inner vertex
detector for STAR
Aluminum/Kapton flex cable under tension
50 ?m Silicon supported under tension
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END