- Performance Studies & Production of the LHCb Silicon Tracker Stefan Koestner (University Zurich) on behalf of the Silicon Tracker Collaboration 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 TT- modules: modules are connected to 14 sensor long ladders ( and ) 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 minimize R/O channels & radiation length:  large pitch O(200  m) (charge collection)  long strips 33cm (noise)  “thin” sensors (little charge) 40MHz, fast readout  (noise) Pulse-Shaping fast readout in O(charge collection time) variable shaper feedback setting in Beetle (V fs )  adapt to different detector capacitances signal remainder 25ns after peak  specification: remainder < 0.5 (TT) < 0.3 (IT) Signal Noise Sensors Kapton Carbon Fibre AIREX faom Carbon Fibre The LHCb experiment: Single-arm forward spectrometer dedicated to B-physics acceptance: (250)mrad TeV, luminosity=2·10 32 cm -2 s bb/year, full B spectrum 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 TT-station: Measures transverse momentum of large impact parameter tracks in L1 active area: 8.2m 2, 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: 4.3m 2, readout channels: ~130k modules: 1, 2sensor-ladders (11 and 22cm) 3 stations with 4 boxes, 4 layers per box (2 stereo):  336modules 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 = ·C tot total capacitance linear with w/p (independent of thickness) parameterization for 320 µm thick sensor 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 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 3σ3σ short broken bond high leakage (irradiation) affects dc-coupled readout easy test for pinholes (bias -0.5V & 0V) -0.5 VoltsNo bias voltage 1.6·10 15 primary pp-collisions (after 10 years) average flux up to ~4· MeV neutron equivalent/cm 2 for 1 sensor sector - (safety factor 2) Other losses in S/N (pessimistic scenario): charge traps increase of total capacitance up to 1· MeV neutrons/cm 2 close to beam pipe GFK CFK S/N Module Production: Readout hybrid and sensors are glued using custom made positioning jigs parallel module production in several jigs Burn-in and Final Readout Test: temperature cycling and readout for module testing IV measurements, Test-pulses, etc Production tested on 4 IT and 7 TT modules so far, almost ready for full production ! Leakage current: I = 20°C ENC 2 =11.56·τ·I Expected depletion voltage according to the “Hamburg Model”: 410µm thick sensors bulk resistivity 4-9 kΩ/cm Low material budget for cooling inside sensitive area: liquid (C 6 F 14 ) cooling for hybrids and module support natural convection on sensor surface to prevent thermal runaway (~5 Wm -2 K -1 ) -