9. september 2010 thomas bergauer (hephy vienna) operation of the cms tracker at the large hadron...
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9. September 2010
Thomas Bergauer (HEPHY Vienna)
Operation of the CMS Tracker at the Large Hadron Collider
ÖPG/FAKT Annual Meeting Salzburg
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Operation of the CMS Tracker at the Large Hadron Collider
CMS: Compact Muon Solenoid
Weight: 12.500 tDiameter: 15 Length: 21.5 m
Weight: 12.500 tDiameter: 15 Length: 21.5 m
SupraconductingMagnet (4 T)
HadronicCalorimeter
ElectromagneticCalorimeter
SiTracker (Pixel and Strips) Muon System
Magnet Return Yoke
Very ForwardCalorimeter
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Operation of the CMS Tracker at the Large Hadron Collider
CMS Silicon Strip Tracker
• Largest silicon tracker built• Active area of 198 m2
– 5.4 m long, 2.4 m diameter
• Components:– Pixel detector
(not covered in this talk)
– TIB (Inner barrel): 4 layers
– TID: 3 Inner Disks
– TOB: (Outer Barrel): 6 layers
– TEC (Endcaps): 9 disks on each side
• Key features:– 9.6 Million readout channels
– Analog readout
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Barrel(BPIX)
Endcap(FPIX)
L ~ 90 cmrmin = 4.4 cmrmax = 10.2 cm
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Operation of the CMS Tracker at the Large Hadron Collider
CMS Tracker in pictures
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Operation of the CMS Tracker at the Large Hadron Collider
CMS Tracker Installation December 2007
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Operation of the CMS Tracker at the Large Hadron Collider
• Angular coverage down to 9 degree to the beam-pipe (|η|<2.5)
• 4 layers and 3 rings contain stereo modules for 2D hit reconstruction
Basic Building Block:
Detector module• 15 148 pieces in total• 15 different geometries• Modules consist of– Carbon fiber/graphite frame– Front-end hybrid with APV25
readout chips– One or two p-on-n silicon
sensor(s), 320/500 micron thick
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Operation of the CMS Tracker at the Large Hadron Collider
Readout Chain
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Operation of the CMS Tracker at the Large Hadron Collider
Commissioning Procedures
• Analog readout– Digitization is done only in off-
detector electronics (FEDs)
• Thus, detector needs to– Time-align internally (different
cable lengths)– Tune laser gain (analog opto-
hybrids)– Optimize chip parameters
(baseline,…)– Determine noise and
pedestals (zero-suppressed data)
• Benefit of analog readout– Higher position resolution– Makes debugging easy
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Operation of the CMS Tracker at the Large Hadron Collider
Operational fraction of SST
• 98.1% of channels in operation
• TIB/TID: 96.3 %– One ring lost (short,
appeared with B field), ~1%
– HV missing and HV shorts, ~2.5%
• TOB: 98.8 %– One ring lost (short,
comes/goes with B field)
• TEC: 99.0 %– One HV PG missing (short)– One LV PG missing (short)
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TID+ TEC+
TID- TEC-
TIB TOB
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Operation of the CMS Tracker at the Large Hadron Collider
Signal-to-Noise Ratios
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TIB TID TOBTEC thin
TEC thick
19.4 18.5 22.5 19.1 23.4
• Charge clusters of
associated tracks– Divided by noise determined
during calibration (pedestal) run
– Non-perpendicular tracks
normalized by trigonometry
• Landau convoluted
with Gaussian – MP value taken for summary
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Operation of the CMS Tracker at the Large Hadron Collider
Tracker Alignment• 15148+1440 sensors
– 6 degree of freedom each
• O(10m) accuracy
• Minimization hit/track residuals 2
• Two approaches:– Millipede (II): Global minimization– “Hits and Impact Points” (HIP): local
minimization of sensor position, iterative, detailed track model
– Kalman Filter-based fit method working on “correlated” elements, iterative
– Applied sequentially • from large substructures to sensor level
• Distributions of Mean Residual (DMR): median of the residual distributions in each sensor
• 2010 cosmics and collision events used for present alignment:
– 1.5M cosmic tracks (p>4 GeV)– 1.7M collision tracks (p>3 GeV)
• with constraint to primary vertex
p>3 GeV/cp
T>0.65GeV/c
Only modules with >200 hits
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Operation of the CMS Tracker at the Large Hadron Collider
Summary
• CMS Tracker (together with whole CMS experiment) performs excellently in both cosmics and pp collision runs
– 98,1 % channels in operation
• Tracker uses analog readout from detector to off-detector electronics
– Makes different calibration runs necessary
• Signal-to-noise ratio meets expectations
• Alignment algorithms reveal accuracy of 10μm
• Tracker contributes to the high quality physics data CMS delivers
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Operation of the CMS Tracker at the Large Hadron Collider
THE ENDThank you for your attention
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Operation of the CMS Tracker at the Large Hadron Collider
APV25 Peak vs. Deconvolution mode
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Deconvolution mode– output charge for each strip represents a
weighted sum of three consecutive pipeline cells
– designed to avoid signal pile-up in high luminosity operations
– necessary whenever bunch separation is less than a few hundred nanoseconds
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Operation of the CMS Tracker at the Large Hadron Collider
Collected Events
• pp Collisions– Dec 2009 (900GeV+2.36 TeV):
~300k MinBias Events– 2010 (7 TeV): ~3000 nb-1
• Cosmics muons– 2008: 3M tracks in tracker– 2009: 4M tracks– 2010: 2.2M tracks
• ~ 4% in pixel detector volume
• alignment, calibration, noise, resolution
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Operation of the CMS Tracker at the Large Hadron Collider
Track Reconstruction Efficency
Tracks reconstructed in three steps:• seeding: hit triplets (mainly pixel hits)
or pairs + beam spot used as track candidate
• Pattern recognition: track candidate propagation (Kalman filter), addition of new compatible measurements, track candidate cleaning
• Final Track Fit: track parameter estimator
• Track Selection: fakes rejected with quality cuts
Iterated several times:• hits associated to reconstructed tracks
are removed• different seeding algorithms• different quality cuts
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Operation of the CMS Tracker at the Large Hadron Collider
Impact parameter
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transverse longitudinal