Performance studies production of the lhcb silicon tracker
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-. GFK. CFK. Production:. Electrical Tests: internal calibration pulses reliable to detect common defects ( broken, short, pinhole ) in final modules simulated defects (artificial bonds) show similar behaviour than real ones. peakheight remainder. broken bond.

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Performance Studies & Production of the LHCb Silicon Tracker

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Performance studies production of the lhcb silicon tracker

-

GFK

CFK

Production:

  • Electrical Tests:

  • internal calibration pulses reliable to detect common defects (broken, short, pinhole) in final modules

  • simulated defects (artificial bonds) show similar behaviour than real ones

peakheight remainder

broken bond

short

  • high leakage (irradiation) affects dc-coupled readout

  • easy test for pinholes (bias voltage @ -0.5V & 0V)

-0.5 Volts

No bias voltage

Stefan Koestner (University Zurich)

on behalf of the Silicon Tracker Collaboration

The LHCb Silicon Tracker:

  • TT- modules:

  • modules are connected to 14 sensor long ladders (4-3-3-4 and 4-2-1-1-2-4)

  • To reduce material inside sensitive area readout hybrids are located at the edges of detector boxes

  • inner sensors connected via Kapton interconnect cable (up to 55cm long)

  • supported by carbon/glass fibre rail

  • high load capacitance: 3 sensor + flex  55 pF

  • inter-strip capacitance 0.17 pF/cm

  • The LHCb experiment:

  • Single-arm forward spectrometer dedicated to B-physics

  • acceptance: 15-300(250)mrad

  • [email protected] TeV, luminosity=2·1032 cm-2s-1

  • 1012 bb/year, full B spectrum

Performance Studies & Productionof the LHCb Silicon Tracker

-

  • The Silicon Tracker:

  • consists of the Trigger Tracker (TT) in front of the magnet and the Inner Tracker (IT) behind the magnet.

  • spatial resolution requirements ~60µm  pitch ~200µm

  • IT - modules:

  • p-n silicon micro-strip sensors (Hamamatsu)

  • 384 AC coupled readout strips, 108 mm long

  • 197µm pitch, w/p=0.25, 320(410) µm thickness

  • readout hybrid with 3 Beetle chips

  • cooling “balcony” for mounting and positioning of the ladder on the supporting cooling rod which is connected to the liquid cooling system

  • Carbon Fibre (CF) support produced out of high thermal conductive fibre used to cool the sensors and the detector box

  • Sensors

  • Kapton

  • Carbon Fibre

  • AIREX faom

  • Carbon Fibre

  • TT-station:

  • Measures transverse momentum of large impact parameter tracks in L1

  • active area: 8.2m2, readout channels: ~180k, cooled to ~5°C

  • modules: 1,2,3-sensor-sectors (11cm, 22cm,33cm )

  • 4 layers in 2 half stations, 2 layers with ±5º stereo angle

  • The Inner Tracker:

  • Provides granularity in the high multiplicity region around the beam pipe - 1.3% of sensitive area  20% of tracks

  • active area: 4.3m2, readout channels: ~130k

  • modules: 1, 2sensor-ladders (11 and 22cm)

  • 3 stations with 4 boxes, 4 layers per box (2 stereo):  336modules

Performance:

Radiation Damage (TT):

  • 1.6·1015 primary pp-collisions (after 10 years)

  • average flux up to ~4·1013 1MeV neutron equivalent/cm2

  • for 1 sensor sector - (safety factor 2)

minimize R/O channels & radiation length:

 large pitch O(200mm)(charge collection)

 long strips 33cm (noise)

 “thin” sensors (little charge)

40MHz, fast readout  (noise)

  • Testbeam Results:

  • 120 GeV pions  ~MIP (minimum ionizing particle)

  • 3 sensor ladders with CMS, GLAST, LHCb sensors (~30cm)

  • 2, 1 sensor ladders with LHCb multigeometry sensors

  • S/N interpolation of on-strip data:

  • ENC = 542 + 49.83·Ctot

  • total capacitance linear with w/p (independent of thickness)

  • parameterization for 320 µm thick sensor

S/N

  • Leakage current:

  • I = α·Φ·V @ 20°C

  • ENC2=11.56·τ·I

  • Pulse-Shaping

  • fast readout in O(charge collection time)

  • variable shaper feedback setting in Beetle (Vfs)  adapt to different detector capacitances

  • S/N interpolation of inter-strip data:

  • charge loss in inter-strip region (trapped on surface)

  • linear as a function of (pitch-width)/thickness (in the range of interest)

  • dominates for pitch wider than ~200 µm

  • Other losses in S/N (pessimistic scenario):

  • charge traps

  • increase of total capacitance

S/N

signal remainder 25ns after peak  specification: remainder < 0.5 (TT)

< 0.3 (IT)

  • Module Production:

  • Readout hybrid and sensors are glued using custom made positioning jigs

  • parallel module production in several jigs

Radiation Damage (IT):

  • up to 1·1013 1MeV neutrons/cm2 close to beam pipe

  • Burn-in and Final Readout Test:

  • temperature cycling and readout for module testing

  • IV measurements, Test-pulses, etc

  • Expected depletion voltage according to the “Hamburg Model”:

  • 410µm thick sensors

  • bulk resistivity 4-9 kΩ/cm

Signal

  • Low material budget for cooling inside sensitive area:

  • liquid (C6F14) cooling for hybrids and module support

  • natural convection on sensor surface to prevent thermal runaway (~5 Wm-2K-1)

Production tested on 4 IT and 7 TT modules so far, almost ready for full production !

Noise


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