A vertex detector for the next linear collider

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A vertex detector for the next linear collider

• Stefania Xella
• on behalf of the LCFI collaboration
• Bristol Univ., Lancaster Univ., Liverpool
  Univ., Oxford Univ., Rutherford
  Appleton Laboratory, Queen Mary University
  London
• hep.ph.liv.ac.uk/green/lcfi/home.html
  

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Next Linear Collider a challenging environment
for a vertex detector

• Main goal of the next linear collider is to
  measure PRECISELY the Higgs boson and possibly
  physics beyond the SM. This requires
• High energy and luminosity, which might mean
• high beam background
• Tesla 50 ms 4 backgr hits/mm2 at 15 mm
  radius
• gt fast detector readout
• Optimal jet/flavour reconstruction due to event
  topology
• ee-gttt 6 jets, 2 b and 2 c flavoured
• ee-gtHA 12 jets, 4 b flavoured
• gt very granular, low material budget
  detector

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Importance of the right design
optimal vertex detector design is most
important, to reach final physics goal !
PRELIMINARY tagging purity vs efficiency
5 layers, 0.1X0
4 layers, 0.2X0
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LCFI collaboration

• Linear Collider Flavour Identification
  collaboration RD work concentrates on a CCD
  pixel device

Mechanical support (RAL PPD/Oxford)
CCD development design/test (RAL
PPD/E2V/ Liverpool)
design optimization from physics (see T.Kuhl
talk) (RAL PPD/Bristol/Lancaster)
Readout IC, Driver IC, (RAL ME/Oxford)
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Current design (I)

• Small pixels (20x20 mm2)
• -gt precise point resolution
• thin detector(lt0.1X0)
• -gt less multiple scattering
• close to the IP (15 mm)
• -gt smaller extrapolation
• error
• large polar angle coverage
• cos(?)lt0.90 with 5 hits
• cos(?)lt0.96 with 3 hits

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Current design (II)

• 5 layers
• -gt higher resolution
• -gt robust local alignment
• -gt effective gamma conversion
• fast readout (50?s/layer)
• -gt sustain high integrated
• background
• gas cooled, low mass foam
• cryostat
• minimal electronics (power
• few optical fibres)
• -gt little material at low angles

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Very challenging !
       
 
Detector SLD Future LC
CCDs 96 120
CCD active area (cm2) 12.8 27.5
n. of pixels (106) 307 799
n. of layers 3 5
inner layer radius(mm) 28 15
layer thickness (Xo) 0.4 0.1
cos(?) max 0.90 (2 hits) 0.96 (3 hits)
readout time (1 layer) 216 ms 50 ms (8 ms NLC)
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Column Parallel CCD (CPCCD)

• Fast readout speed only with Column parallel
  readout new design!
• Serial register omitted
• 50 Mpixels/sec from each column
• Image section clocked at high frequency
• Each column has its own ADC/amplifier

M
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Readout chip (CPR)

• CMOS circuit bump bonded to the CCD
• Each column has amplifier and ADC
• Correlated double sampling for low noise
• Sparsification done in the chip
• Buffer memory and I/O interface

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Ladder end

• Bump bonding CPCCD-CPR
• Driver IC provides high frequency (50MHz), low
  voltage (1.5V pp) clocks
• 2-phase driven CCD
• Low inductance connections and layout
• Small clock and digital feedthrough

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Device simulations

• ISE-TCAD software used at RAL. Mostly important
• To check feasibility of current design
• Foresee show-stoppers
• Test new ideas

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Status of RD program

• 5 or 6 stage RD program in collaboration with
  E2V (former Marconi Applied Technology) company
  in the UK
• Test for high speed CCD readout (up to
  50MPix/sec) successfully carried out on standard
  CCD58 device, in serial register
• Test for radiation damage at different
  temperatures/RO frequency being carried out
• CPCCD-1 and CPR-0,1 are (being) produced.
• Testing during end2002/beg2003
• Several options for mechanical support design
  currently investigated (unsupported/semi-supported
  )

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First CPCCD-CPR

• 2 different charge transfer regions
• 3 types of output circuitry
• Independent CPCCD and CPR test possible
• Designed to work in almost any case!

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First CPR tests

• 0.25 mm CMOS
• Charge transfer amplifier (CTA) in each ADC
  comparator
• Designed to work up to 50 MHz
• First CPR produced small chip (2x6mm), testing
  flash ADC and voltage amplifiers. Very promising
  results.
• Next CPR contains CTA,ADC,FIFO memory in 20 mm
  pitch

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Tests of high speed CCD

• E2V CCD58
• 3-phase driven CCD
• Classical readout
• (serial register)
• 12 ?m 2 pixels
• 2 outputs
• 2x106 pixels in two sections

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Tests of high speed CCD

• 55Fe X-ray spectrum at 50 Mpix/s
• MIP-like signal (5.9 keV X-rays generate ? 1620
  electrons)
• Low noise ? 50 electrons at 50 MHz clocks
• CCD58 is designed to work with large signals
  at 10 Vpp clocks
• No performance deterioration down to 5
  Vpp clocks
• Still good even at 3 Vpp clocks

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low drive voltage/CTI
Clock traces and 55Fe spectrum for low drive
voltages at 50 Mpix/sec

• Radiation damage effects
• beam background expected
• about 50krad/year
• (neutron 5x109/cm2/year)
• CTI should improve at fast
• readout to be verified
• CCD58 can be flexibly clocked from 1 to 50 MHZ,
  so it should be possible to obtain good results
  for CTE

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Mechanical support RD

• Final goal is to design a CCD support structure
  with
• Low mass (lt 0.1 Xo)
• Stable shape under repeated temperature cycles
  down to 100oC
• Minimum metastability and hysteresis effects
• Compatible with bump bonding
• Robust assembly
• Able to undergo gentle gas cooling

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Thin ladder options

• Unsupported CCD thinned to 50 mm and held under
  tension. Tested experimentally
• sagitta stability found better than 2 mm
  at Tgt2N, but
• large differential contraction at CCD
  surface causes lateral curling design is
  difficult to handle
• Semi-supported CCD thinned to 20 mm and attached
  to thin (not rigid) Be support, held under
  tension. Tested in ANSYS simulation
• CCD surface may become dimpled under
  study
• may need fine pitched matrix of glue
  difficult?
• gt still lots of work to do and ideas to test

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Thin ladder options
CCD (20 µm thin) bonded with adhesive pads to 250
µm Be substrate On cooling adhesive contracts
more than Be ? pulls Si down on to Be
surface Layer thickness ? 0.12 Xo 1 mm diameter
adhesive columns inside 2 mm diameter wells 200
µm deep in Be substrate
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Summary

• The LCFI collaboration RD program is
• vast, and very challenging.
• Its aim is to provide a
• fast and low material budget CCD based pixel
  detector
• to maximize the physics potential of the next
  linear
• collider
• We are only at the first stage of a long RD
  program, so stay tuned to hear more !

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Backup slides
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Backgrounds at the nlc
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CPR-1

• In CPR-1
• Voltage amplifiers for source follower
  outputs from the CPCCD
• Charge amplifiers for the direct connections
  to the CPCCD output nodes
• Amplifier gain in both cases 100 mV for 2000
  e- signal
• Noise below 100 e- RMS (simulated)
• Direct connection and charge amplifier have many
  advantages
• Eliminate source followers in the CCD
• Reduce power ? 5 times to ? 1 mW/channel
• Programmable decay time constant (baseline
  restoration)
• ADC full range ? 100 mV, AC coupled, Correlated
  Double Sampling built-in (CTA does it)

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Semi-supported silicon
Carbon fibre support
Aerogel support
Carbon fibre CTE is tunable, layers can have
optimal orientation and fibre diameter, difficult
to simulate Aerogel support chemically bonds to
Si, aerogel in compression Many other ideas CVD
diamond, vacuum retention, etc