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