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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
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
2Thomas Bergauer (HEPHY Vienna)9. September 2010
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
3Thomas Bergauer (HEPHY Vienna)9. September 2010
Barrel(BPIX)
Endcap(FPIX)
L ~ 90 cmrmin = 4.4 cmrmax = 10.2 cm
Operation of the CMS Tracker at the Large Hadron Collider
CMS Tracker in pictures
4Thomas Bergauer (HEPHY Vienna)9. September 2010
Operation of the CMS Tracker at the Large Hadron Collider
CMS Tracker Installation December 2007
5Thomas Bergauer (HEPHY Vienna)9. September 2010
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
Thomas Bergauer (HEPHY Vienna)9. September 2010 6
Operation of the CMS Tracker at the Large Hadron Collider
Readout Chain
7Thomas Bergauer (HEPHY Vienna)9. September 2010
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
8Thomas Bergauer (HEPHY Vienna)9. September 2010
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)
9Thomas Bergauer (HEPHY Vienna)9. September 2010
TID+ TEC+
TID- TEC-
TIB TOB
Operation of the CMS Tracker at the Large Hadron Collider
Signal-to-Noise Ratios
10Thomas Bergauer (HEPHY Vienna)9. September 2010
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
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
11Thomas Bergauer (HEPHY Vienna)9. September 2010
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
12Thomas Bergauer (HEPHY Vienna)9. September 2010
Operation of the CMS Tracker at the Large Hadron Collider
THE ENDThank you for your attention
13Thomas Bergauer (HEPHY Vienna)9. September 2010
Operation of the CMS Tracker at the Large Hadron Collider
APV25 Peak vs. Deconvolution mode
14Thomas Bergauer (HEPHY Vienna)9. September 2010
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
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
15Thomas Bergauer (HEPHY Vienna)9. September 2010
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
16Thomas Bergauer (HEPHY Vienna)9. September 2010
Operation of the CMS Tracker at the Large Hadron Collider
Impact parameter
17Thomas Bergauer (HEPHY Vienna)9. September 2010
transverse longitudinal