LHCb Vertex Detector and Beetle Chip

1
LHCb Vertex Locator present and future
Martin van Beuzekom On behalf of the LHCb VELO
group
Liverpool University

• Outline
• Introduction to LHCb and VErtex LOcator (VELO)
• Status of VELO
• Beamtests
• Upgrades
• Summary

2
LHCb overview
interaction region

• LHCb
• Studies physics of b-flavoured hadrons (CP
  violation)
• B-hadrons produced at small angles
• -gt Single arm forward spectrometer
• 10 300 (250) mrad in bending plane (non bend.)
• Luminosity 21032 cm-2 s-1

• Large Hadron Collider
• pp collisions vs 14 TeV
• bunch crossing every 25 ns

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Vertex Locator

• 2 retractable detector halves
• Range 3 cm each
• 23 silicon microstrip modules / side
• Silicon modules in secondary vacuum

(2 mm)

• Modules separated from beam vacuum (10-9) by 300
  mm Alu foil (RF box)
• Maximum allowed diff. pressure 5 mbar
• Shield against beam induced EMI
• Innermost strip 8 mm from beam

4
Silicon sensor details
R-measuring sensor (45 degree circular segments)

• 300 mm thick sensors
• n-on-n, DOFZ wafers
• 42 mm radius
• AC coupled, double metal
• 2048 strips / sensor
• Pitch from 40 to 100 mm
• Produced by Micron Semiconductor

42 mm
8 mm
F-measuring sensor (radial strips with a stereo
angle)
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Module construction
Beetle

• 4 layer kapton circuit
• Heat transport with TPG
• Readout with 16 Beetle chips
• 128 channels, 25 ns shaping time,
• analog pipeline
• 0.25 mm CMOS
• no performance loss up to 40 Mrad
• Yield gt 80

Kapton hybrid
Carbon fibre
Thermal Pyrolytic Graphite (TPG)
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Silicon microstrip modules

• 21 stations with R-F geometry
• Fast R-Z tracking in trigger farm
• Overlap of right and left det. halves
• Total of 176k strips
• 2 stations with R-sensor for PileUp trigger

Carbon fibre base
Fine pitch kapton cables
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Pile Up (veto) trigger

• PileUp system detects multiple interactions
• Vetoes Level-0 trigger
• Increases physics output
• Multiple interactions complicate Level-1 trigger
  (CPU-farm)
• Factor 3 reduction in crossings with multiple
  interactions
• 2 R-sensors, prompt binary readout
• Combine 4 strips in 1 to reduce inputs
• 2048 bits _at_ 40 MHz 80 Gbit/sec
• Special hybrids (4 times signals)

LHCb luminosity
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PileUp continued
all combinations
true tracks

• Each vertex bin corresponds to a small wedge in
  the RA-RB correlation plot
• Each track is represented by a point
• Histogramming of Z-vertex
• determine vertices with FPGAs
• find 1st peak, mask hits,
• find 2nd peak
• Algorithm highly pipelined
• ( 80 Bunch crossings)

2 vertices
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LHCb status
Installation progressing, first collisions
expected in fall 2007
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Status _at_ Interaction point

• Vacuum vessel installed May 2006
• Vacuum controlled by PLC
• Movement system controlled by PLC
• Thin (2 mm) exit foil mounted in Aug 2006
• Vacuum qualification ongoing
• Detector installation early 2007

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CO2 cooling

• 2 phase CO2 cooling system
• Low mass
• Radiation hard
• Non toxic
• Silicon modules in parallel
• 1 mm Ø stainless steel capillaries
• Pressure up to 70 bar
• Large DT over TPG interface
• heat load max. 30W

T-30 ºC
T -5 ºC
12
Testbeam performance

• 2004
• Single sided module with 200 mm sensor
• Characterized (final) sensor (final) Beetle
• S/N 16
• Spillover _at_25 ns lt 25
• Resolution 4 mm

Beetle Frontend pulseshape

• August 2006
• 3 double sided modules
• Full electronics chain with final electronics
• ADCs, Timing, Fast Slow Control
• Data taken for many sensor and chip settings
• Analysis ongoing

• November 2006
• Aim for a complete detector half (21 mod.)
• Module production in Liverpool at full speed
• Delivery 4 modules per week
• Major effort!

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VELO Upgrades

• Why
• Limited lifetime of VELO due to high radiation
  dose
• (1.3x1014 neq/cm2/year)
• Improve (impact parameter) resolution
• Displaced vertex trigger
• Increase statistics
• Readout of complete LHCb detector _at_ 40 MHz
• How
• Different sensor technology/geometry
• Reduce material in VELO
• Move closer to beam
• Currently 8 mm, goal 5 mm (min. allowed by
  accelerator)
• Up to 36 resolution improvement
• Increase luminosity (not SLHC)
• Level-1 computing power

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Radiation environment

• Radiation environment for current design
• Strongly non-uniform
• Dependence on radius and z-position
• Max fluence 1.3x1014 neq/cm2/year
• Define as 1 LHCb-year
• Expected (useful) lifetime 3 years
• assuming nominal luminosity
• no accidents

• With upgrades
• 5 mm strip radius -gt 2.5x increase
• Luminosity to 1x1033 -gt 5x increase
• Fluence 1.7x1015 neq/cm2/year
• Only possible with
• Different sensor technology
• and/or smaller strips or pixels (Syracuse group)

15
Radiation Hard Technologies
Magnetic Czochralski

• p-on-n MCz
• Assume required CCE min. 60
• Single sided processing
• RD by Glasgow group

5..6 LHCb-years
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Radiation Hard Technologies- II
n-on-p
gt 20 LHCb-years

• High resistivity p-silicon
• Single sided processing
• Very high bias voltage
• RD by Liverpool group

Presentation by Gian-Luigi Casse
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Radiation Hard Technologies- III
3D - sensors

• Extremely radiation hard
• Low bias voltage
• Very promising
• Complex processing
• RD by Glasgow group

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Reduce material in VELO

• Radiation length of total VELO 19 X0
• Largest contribution from RF-foil and sensors
• Thin sensors (200 mm) already tested extensively
  
• Thinner RF-foil is under investigation

• BTeV planned sensors in primary vacuum
• Beam (mirror) current via wires/strips
• Cryo pumping against outgassing
• Totem (_at_LHC)
• 150 mm Inconel (Ni-Cr) foil 1 mm from beam

19
Summary

• Construction of LHCb VErtex LOcator is well
  underway
• Mechanics, vacuum, motion system installed
• Cooling system steadily progressing
• Silicon module production at full speed
• Next deadline is half detector for November
  testbeam
• Detector (sensors) installation early 2007
• Already starting to think about upgrades
• Limited lifetime of VELO
• More radiation hard sensors
• Reduce material to improve performance