Performance Studies & Production of the LHCb Silicon Tracker

1. - 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 3σ • 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 • pp@14 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