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DT Barrel Alignment Using Standalone Muon Tracks
Luca ScodellaroMuon Barrel Workshop
February 24th, 2011
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Outline• Brief remind of the methods• MC analysis set up• Reconstructing barrel geometry: ◊ Sectors ◊ Sector connection ◊ Wheels ◊ Whole barrel• Final remarks
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Brief Remind of the Method
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Standalone Geometry with Tracks• Hardware alignment close to its design precision• Alignment with respect to the tracker might suffer
for several effects: ◊ Tracker misalign., B field, material description• Exploring a third source of information: SA tracks• Millipede approach based on a linear
approximation of residuals: R = B∆p + Aδ• B matrix hard to describe in a non-uniform
magnetic field
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Standalone Geometry with Tracks• Trying an approach based on DT segments: ◊ Selecting tracks with pT>50 GeV/c ◊ For small movements, we can assume ∆p to depend only on chamber movements B ∆p = ACδinit = A’δfinal ◊ Simplified χ2 minimization
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MC Analysis Set Up
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Studies on MC• We want to understand the sensitivity we can
reach on ideal MC • MC sample: ◊ CosmicMC_BON_10GeV_22X_V6_MuAlStandalone• Using 1Leg tracks used to improve pT
measurements ◊ Same performances with 2Leg tracks and 2
iterations• The idea is to start from HW based alignment• A misalignment scenario has been generated by
smearing ideal positions (local frame) by: ◊ Center of the chamber: 400 μm ◊ Orientation: 400 μrad
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Validation of the Fits• We reconstruct objects (sectors, wheel,
etc.) in a standalone way • When comparing two geometries for an
object, we look at the local coordinate of each chamber in a geometry in the reference system of the same chamber in the other geometry
• The global transformation which minimize these coordinates is computed
• Resulting local coordinates are presented
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Reconstructing Sectors
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Chamber to Chamber Fit• Residual distribution for YB0, Sector 10, Station
2Misaligned geometryCorrected geometry (1 iter.)
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Chamber to Chamber Performance• Performance in chamber alignment vs. number
of segments used
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Sector Recontruction Performance• Distance of chamber position from ideal
geometry
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Sector Recontruction Performance• Performance in sector alignment vs number of
segments in the chamber with lowest statistics
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Sector Connection
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Sector Connection Strategies• All chamber to chamber approach (All
C2C): ◊ Treat all chamber separately ◊ Compute at the same time internal sector
structure and sector relative position ◊ Alignment matrix A is 20x36
• Sector to sector approach (S2S): ◊ Froze sector structure ◊ Fit relative sector position by using segments from crossing tracks ◊ Alignment matrix A is 20x6
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Sector Connection Performance• Sector connection performance for All C2C and
S2S:
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Sector Connection Performance• Sector connection performance with All C2C vs
number of segments in the chamber with highest statistics
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Reconstructing Wheels
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Wheel Reconstruction• WheelS2S: using S2S strategy and fitting all
sectors in a wheel together (A~172x258)
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Wheel Reconstruction• Details on the performance in local Y for subsets of
sectors (all wheel was fitted)
Sectors Mean ΔY Mis. (μm)
RMS ΔY Mis. (μm)
Mean ΔY Algn. (μm)
RMS Δ Y Algn. (μm)
2 to 6 -12 286 6 1518 to 12 39 258 -18 1485 to 9 24 235 10 2556 t0 8 14 196 -11 22511 to 3 28 280 -21 25312 to 2 14 217 -1 177
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Wheel Reconstruction• Sector connection comparison for S2S and
WheelS2S• WheelS2S connect the sectors as S2S (no
degradation)
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Reconstructing Whole Barrel
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Barrel Reconstruction• Wheel2Wheel: same strategy as for WheelS2S but
using frozen wheels instead of frozen sectors
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Final Remarks• Studies of standalone barrel alignment with MC
cosmics basically complete• Testing on data ongoing: ◊ Cosmics first: low statistics for certain barrel region,
and ttrig not optimal ◊ Collisions data: better ttrig, better relative statistics
between sector/wheel, no as much muon with high pT, no 1leg tracks
◊ Could use different datasets for each alignment step
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Backup Material
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Sector Recontruction Performance• Sector reconstruction with 1 leg tracks and 2 leg
(2 iterations) tracks
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Chamber to Chamber Performance• Performance in the alignment of chambers
between sectors
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Distribution of Segments in Cosmics
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Sectors
Whe
els
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Sector Connection Performance• Sector connection performance for All C2C and
S2S strategies
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Distribution of Segments in Cosmics
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Sectors
Whe
els