First Reconstruction ResultsFirst Reconstruction Resultson the Alignment of Muon on the Alignment of Muon Endcap Chambers in the Endcap Chambers in the CMS Experiment at CERNCMS Experiment at CERN
S. Guragain, G. Baksay, M. Hohlmann
Florida Tech
74th Annual meeting of SESAPS, Nashville, TN, Nov 8-10, 2007
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CMS detector of LHC @ CERNCMS detector of LHC @ CERN
CMS solenoid -13 m long
Magnetic field - 4 TeslaTotal weight - 12500 tOverall diameter -15 m
Overall length - 21.6 m
Muon Endcaps
ME+1ME+2ME+3ME+4
ME -
Z+
Compact Muon Solenoid
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A part of CMSA part of CMS
2 Crosshair Lasers (adjustable)
Ref. DCOPS
Chamber DCOPS’s
Transfer Line
DCOPS
Z-tube
Z-sensors
Transfer Plate
Clinometer
MountingTower
ME+2 SLM
BackCham
ber
R-sensor
Laser beam
Laser on !ZCMS
RphiCMS
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Full Reconstruction ModelFull Reconstruction Model
R-sensors
Z-sensors
Note: only smallsample of analog sensors shown
ClinometersTransfer plate
DCOPS’s
Straight Line Monitors (SLMs)and Transfer lines
Lasers
SLM currently under study (ME+2 SLM 2-5)
Lasers
Chamber resolution 75 micron for ME1/2
and 150micron for other.
The system monitors the positions of
CSCs relative to each other and to the
MABs
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Basic strategyBasic strategy
• Fit DCOPS data at B=0T and reconstruct DCOPS and CSC positions using COCOA (CMS Object-oriented Code for Optical Alignment)
• Check B=0T reco results for one SLM against photogrammetry (PG) in full detail and with great care until we can trust the reconstruction
• Quantify precisions and accuracies
• Reconstruct DCOPS & CSC positions at B=4T
• Apply lessons learned to reco of other SLMs
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Simultaneous fit in zSimultaneous fit in zCMS CMS for two for two
lasers in ME+2 SLM2-5 at B=0Tlasers in ME+2 SLM2-5 at B=0T
DCOPSCCDs
B=0T
Laser hits(shifted to the sides of CCDs for display)
CCD2 CCD4CCD2 CCD4
fitted position
First CCD pixels
Simultaneous fitting of 2 laserswith hits that overlap on 4 central
DCOPS’s is now working !
Ref. CCDRef. CCD
bad hitsnot usedin fit
Note: In MTCC 2006 the lasers were tilted towards the CSCs on purpose to compensate for disk bending at B=4T !
laser line fitlaser line fit
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Fit ResidualsFit Residuals
Precision in zCMS (“z-resolution”) ≈ 60 m
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Dowel pins
Reconstructed tops of CSC Alignment pins
Reconstructed tops of DCOPS boxes
First CCD pixels
Reconstructed positions of outer CSC PCB skins
B=0T
CCDs
PG of TPsdeterminesglobal zCMS
position of entire system
Reconstructed DCOPS & CSC Reconstructed DCOPS & CSC Positions and their PrecisionPositions and their Precision
Note: In this coordinate system the DCOPS are“up-side-down” (ME+2 DCOPS tops are at smaller zCMS)
zreco~ 270 m
Shimdelta
Newshim
Newshim
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Now, accuracy …
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Solid triangles: Reconstructed tops
of CSC Alignment pins
Solid triangles: Reconstructed tops of DCOPS boxes
First CCD pixels
Reconstructed positions of outer CSC PCB skins
B=0T
CCDs
PG of TPsdeterminesglobal zCMS
position of entire system
Accuracy check of ABSOLUTE Accuracy check of ABSOLUTE positions against PG at B=0Tpositions against PG at B=0T
Open triangles: PG measurement of tops of DCOPS boxes
Open triangles: PG meas. of
CSC Alignment pins
PG measurements of coded targets on outer CSC PCB skins
Reco and PG now match well !!!
Perfect !
(no PG avail.)
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Discrepancy in Z between Discrepancy in Z between PG and Fitted positionsPG and Fitted positions
683 micron
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Reconstruction of zReconstruction of zCMS CMS for for
CSCs in ME+2 SLM2-5 at B=4TCSCs in ME+2 SLM2-5 at B=4T
B=4T
B=0T fit positions
B=4T fitted CSC positions
Disk bending is reconstructed !This assumes (incorrectly) that the TP’s donot shift in z &do not rotate!
~ 13mm
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SummarySummary• Reconstruction of zCMS coordinate is working
• Z-resolution & Sensitivity to relative motion ≈ 60 m
• Z-precision of reconstructed CSC centers ≈ 270 m
• Z-accuracy of reconstruction ≈ 680 m (Comparison with Photogrammetry data) Accuracy required by design 1 mm
• Disk bending at B=4T is reconstructed
THANKS
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Back up slides
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ME+2 DiskME+2 Disk
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Beam Profiles measured with CCDs 2 & 4 Beam Profiles measured with CCDs 2 & 4 in ME+2 SLM2-5 for both Lasersin ME+2 SLM2-5 for both Lasers
Laser Beam Profiles supplied by Jim Bellinger
Pt.5Pt.2 One MTCC2 alignment event: Nov 3, 2006 00:01:16:48
CCDs 4
Laser 2
CCDs 2 in 10 DCOPS
Good hits !
Laser 2
Laser 5
Laser 5
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Reconstructing ABSOLUTE CSC Reconstructing ABSOLUTE CSC zzCMSCMS- coordinates via DCOPS geometry…- coordinates via DCOPS geometry…
z-coordinate of first CCD pixel(14 m/pixel × 1024 pixels)
z-reference surface for DCOPS dowel pin (new!)
nominal zCMS- position for SLM
updated CAD Drawing by Dave Eartly – 10/15/07
CCD
Top of DCOPS box
DCOPS foot
Dowel pin (precision element)center
AllowedLaser Range
CCDs2 & 4
All dimensions in mm
DCOPS Side View
+
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z-coordinate of first CCD pixel
z-reference surface for DCOPS dowel pin
nominal zCMS- position for SLMCCD
Top of DCOPS box z-coord. of PG Target on top of DCOPS box
Shim
Mounting plate
Mounting barDCOPS foot
top CSC PCB panel
updated CAD Drawing by Dave Eartly – 10/15/07
CSC z-reference surface for al. reco (new!)
coded PG target
lives here !
CSCframe
… … CSC geometry…CSC geometry…
38
.19
4
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……and Transfer Plate (TP) geometryand Transfer Plate (TP) geometry
TP ref. surface (also for PG)
SLM Reference DCOPS
Transfer Line DCOPS
Laser
6.73 (newly found shim !)
updated CAD Drawing by Dave Eartly – 10/17/07
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Sanity check on Precision as Sanity check on Precision as returned by Reconstructionreturned by Reconstruction
All errors in microns
All tolerancesIn this columnunder review !
Precision dominated by mechanical tolerances and not by spread of laser hits in fit (60 m res.) !
ok !
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Effect of missing hitsEffect of missing hits
This Example: Turn onegood hit into a bad hit on two separate DCOPS on the same chamber
Result:This has only a small effect on the overall fit and reconstructed positions !
Simulate effect of missing laser hits (e.g. due to shadowing) on the reco results by manually inflating errors on good hits
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Effect of missing hits cont’dEffect of missing hits cont’d
Chambers MEp2_2_08 MEp2_1_14 MEp2_2_08 MEp2_2_08
1 7 DCOPS included and 3 DCOPS excluded (Original positions) 8096.52 mm 8097.02 mm 8097.95 mm 8095.92 mm
Ids for forced bad hits Shifts in Measurement (mm) Error (micron) Shift (micron) Shift (micron) Shift (micron) Shift (micron)
2 ID 7 L 0 10000 0 0 0 0
3 ID 7 L 0 5000 0 0 0 0
4 ID 7 L 20 17 6170 4800 2370 2370
5 ID 7 L, 6 L 0 10000 30 -20 10 10
6 ID 7 L, 6 LR 0 10000 20 -20 10 10
7 ID 7 L, 6 LR, 16 LR 0 10000 10 880 -10 -10
8 ID 7 L, 6 LR, 16 LR, 17 UDLR 0 10000 -60 660 -50 -50
9 ID 7 LR, 6 LR, 16 LR, 17 UDLR 0 10000 -60 -40 -50 -50
10 ID 1-7 all Left CCDs 0 10000 -200 -140 -440 -440
11 Id 3 L (10 mm error) 0 10000 0 0 -190 -190