10 th INTERNATIONAL CONFERENCE ON INSTRUMENTATION FOR COLLIDING BEAM PHYSICS Budker Institute of Nuclear Physics, Siberian Branch of Russian Academy of Science, Novosibirsk, Russia February 28 - March 5, 2008 Operation of the CDF Silicon Detector

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia2  At the core of the CDF detector  Largest operating silicon detector  7-8 concentric layers of silicon  7 m 2 of silicon with 1.2 cm < r < 32 cm  722,432 cha., 5644 chips, 704 sensors Silicon Detectors at CDF Silicon will have to survive through Run IIb (6/8 fb -1 )  Designed only for Run IIa (~2/3fb -1 )  Upgrade for Run IIb was cancelled!

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia3 Silicon Sub-detectors  Three Sub-detectors  SVX II: 5 double sided layers  Intermediate Silicon Layers (ISL): 3 double sided layers  Layer 00 (L00): Single sided, LHC-style sensors

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia4 Sub-detector: SVX II  SVX II: The core of the silicon systems  Overall dimensions:  1 meter along beam direction  Radii from 2.5 to 10.6 cm  Structure: three identical barrels  2 bulkheads  12 wedges  5 concentric silicon layers  Silicon layers  Strip pitch: 60 to 140  m  Layers 0,1 and 3 (Axial and 90º strips)  Layers 2 and 4 (axial and 1.2º strips) SVX II barrel SVX II before installation

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia5 Sub-detector: L00  Layer 00: Right onto the beam pipe  Overall dimensions:  1 meter along beam direction  Radii from 1.2 to 2.1 cm  Structure: one single layer  2 bulkheads –Three consecutive sensors  6 wedges  Silicon layers  Strip pitch: 25  m  Axial strips  Radiation tolerant (LHC style) L00 during installation 1.2 cm 2.1 cm

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia6 Sub-detector: ISL  ISL: Intermediate Silicon Layers  Overall dimensions:  1.9 m along beam direction  Radii from 20.5 to 29 cm  Structure: three different barrels  Central: Single layer,14 wedges  Forward: Two layers,12 and 18 wedges  Each barrel two bulkheads  Silicon layers  Strip pitch: 55  m  Axial and 1.2º strips ISL sensors

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia7 Operational Issues During commissioning:  Blocked Cooling lines  Blocked by glue, well inside the detector  Solution: open them up with a powerful laser  Resonances  Wire bonds  to the magnetic field  Synch. Readout  wire oscillate and break  Solution: Stop high frequency synchronous readouts.  Beam Incidents  High dose accidentally delivered to the detector  Solution:  Collimators in key parts of the Tevatron  New Diamond based BLM system. After commissioning: Infrastructure & Aging Jumper B groove left by beam

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia8 Infrastructure & Aging: Power Supplies  Common failure modes of CAEN SY527  Communication loss  Corrupted read back of voltages/currents  Spontaneous switch off  Failure mode of power supply modules:  Voltages in Analog, Digital and Port-Card supply start slowly dropping.  Up to 47 Power supplies started to show this.  Problem:  aging of one type of capacitor  36 capacitors per power supply  Can result in bit errors  Solution:  Wait for the shutdown of September 2007 and …  take all faulty power supplies out  replace all 36 capacitors (on FNAL site)  put them back in and test them on location.  Time intensive effort, lasted about 2 months.  Not enough time to change all  Still expect to replace others as failure appears All power supplies with this failure were replaced!

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia9 Infrastructure & Aging: Cooling Lines  Cooling Lines  Symptoms: electronic-valves start failing.  Problem: ISL cooling line (10% glycol in water) became ACIDIC (ph=2) during the 2006 shutdown  Solution: coolant neutralized by draining and larger use of de-ionizing resin bed  Welds of the aluminum rings that cool optical transmitter had already been corroded  One meter from the closest accessible point  Why there ?  Corrosion-resistance: is alloy-dependent  Heat affected zone around junctions manifold most sensitive (alloy: 6061-Al).  Ion chromatography analysis showed carboxylic acids, mostly formic acid.  Likely came from the oxidation of glycol

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia10 Infrastructure & Aging: Cooling Lines Repair  Started shutdown of 2007:  Keep the silicon cold and dry at all times  A plastic tent was setup to work.  A custom made air dryer changed the volume every 2 minutes.  Dew Point was always kept below -10 Cº.  Basic Idea:  Cover holes with epoxy from the inside of the pipe  using borescopes and catheters.  Repairs took a month  4 shifts of people  Current tests:  Tight vacuum in the repaired lines Hole Repaired cooling system has been running stable for months !

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia11 Environmental Effects on Silicon Sensors  Radiation effects:  Modifies the crystal structure of the sensor bulk.  Intrinsic parameters change with time.  P-N junction evolves, and eventually disappears with time.  Annealing effects:  Due to temperature change of the sensors.  Defects created by radiation are strongly affected.  Performance of the sensor degrading with time: AGING  Depletion voltage increases with time.  Sensor has a maximum breakdown voltage.  Can we fully deplete the sensor until the last day of operation ?  Signal decreases with time and noise increases with time  Can we keep good signal and noise levels until the last day of operation ?

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia12  Measured using more than 1000 thermo-luminescent dosimeters (TLDs)  Two different data-taking periods allowed for distinction between fields:  Radiation field is collision-dominated and scales with Radiation Field (See R. J. Tesarek et al., IEEE NSS 2003) due to beam lossesdue to pp collisions pp How this field affects the silicon sensors ?

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia13 Depletion Voltage: Signal Vs Bias  Look at the charge collection distribution  Reconstruct a track w/o using the studied sensor  If track points to hit in sensor record its charge  Charge collection distribution  Follows a landau distribution  Distribution is smeared by intrinsic noise  Fit the curve to a Landau convoluted by Gaussian (4 parameter fit)  Depletion Voltage:  Maximal for a fully depleted sensor  Study charge collection as function of V BIAS  Identify charge of Most Probably Value (MPV) in each distribution

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia14 Depletion Voltage: Signal Vs. Bias  Plot charge’s Most Probable Value for different bias voltages  Fit to a sigmoid (parameters include the plateau of maximum charge)  Define depletion voltage V d  Our criteria: voltage that collects 95% of the charge at the plateau  Depletion Voltage as a function of luminosity  3 rd order polynomial fit around the inversion point  Linear fit to extrapolate to the future

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia15 Depletion Voltage: Noise Vs Bias  Take advantage of double sided sensors, that have strips on the back side  Depletion zone grows from the p + side  Noise on the other side’s strips (n + ) reduce when the depletion zone reaches them.  Need a criteria for defining V d  We use 95% reduction in noise between the two plateaus  No beam required  no interference with data-taking  Does not work after the sensor underwent inversion.  Depletion zone generated differently

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia16 Depletion Voltage: Results  Prediction for L00  Depends on type of sensor  Oxygenated ladders invert much later  Prediction for SVX-L0 We should be able to deplete sensors until the end of Run II

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia17 Signal to Noise Ratio  Signal  Use J/    +  - tracks  Get total charge of cluster  Decrease linearly with Lum.  Mean Strip Noise  Average over strips in charge cluster  Obtained from calibrations taken every two week.  Square root increase with Lum.  The figure of merit of the performance is the Signal to Noise Ratio (S/N)  Signal: charge collected when a charged particle crossed the sensor  Noise: intrinsic noise of the detector

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia18 Signal to Noise Ratio  Fit of S/N  Limit I: S/N=8 (SVT eff.)  S/N = 6, ~5% loss in SVT eff.  Limit II: S/N=3 (B tag eff.)  Sensor-type behavior  Layers 2,4 (Micron)  Layers 0,1,3 (Hamamatsu)  First layer  careful monitoring to see if it is going to be useful at 4/5 fb -1. Most of the silicon layers will be fully operational until the end of Run II

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia19 Conclusions  Operational Issues:  Advice : expect the unexpected.  We have recovered cooling to the full detector subsystems.  Power supply modules with unstable voltages fixed at FNAL  Sensor Aging  Data indicates that we will be able to fully deplete the sensors  The innermost layers of the detector have passed type inversion  Studies indicate we will remain with a very effective S/N ratio. The CDF Run II Silicon Detector will continue successful operation for the rest of Run II !!

Backup Slides

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia21  Bias current increases with integrated radiation  Theory:  Can be used to obtain flux  Comparison with TLD’s prediction Radiation Effects on Silicon Sensor sensor’s volume damage factor fluence (See R. J. Tesarek et al., IEEE NSS 2003)

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia22  Fermilab (1967)  Large number of H.E.P. projects  Tevatron Run II (2001–2009)  Proton-antiproton collider  Two multi-purpose detectors  CDF & DØ 2 km Tevatron [Fermilab Visual Media Service] Fermi National Accelerator Laboratory – Aerial View  Proton-antiproton collider  √s = 1.96 TeV, 36×36 bunches  Record instant. peak luminosity 292 µb –1 s –1 (1 µb –1 s –1  10 –30 cm –2 s –1 )  Expect 6–8 fb –1 by end of Run II Fermilab and the Tevatron

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia23 Main Purpose of Silicon Detectors  Precision tracking  Momentum measurement  From track curvature  Impact parameter  Closest distance between track helix and z-axis:  Need precision tracking point close to primary interaction  B-tagging  Identification of jets originating from B mesons  Long-lived B mesons (cτ ≈ 500 µm) lead to displaced vertices.  Resolution about 50  m  CDF triggers on displaced vertexes  Silicon needs to be readout at L1A (up to 35 kHz) Missing ET b-tag 1.2 cm jet x y Double “tagged” event in Layer 00 of CDF silicon detector

Feb 29th, 2008Ricardo Eusebi - INSTR 08, Novosibirsk, Russia24 Silicon detectors: Basic functioning  Bulk of material is n -, implants of p + : Intrinsic parameters of the sensor  Charge particle moving through  ions  Problem: free charge carriers overwhelm ionization carriers  Solution: remove free charge carriers  Volume w/o free carriers = depleted  Depletion (w) depends on bias (V BIAS )  The higher the Bias voltage  Higher depletion volume  higher charge collection  V BIAS chosen to fully deplete the bulk This is the operational point of a silicon sensor