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Muon Alignment: Organization. MUIB. Organization New co-coordinator: Jim Pivarski (to be formalized at MUIB) The sign-off chain is formalized, but long: we'll need to have a common decision on a muon geometry within the group a few weeks in advance of the CMS-wide sign-off.

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Muon Alignment: Organization


  • Organization
    • New co-coordinator: Jim Pivarski (to be formalized at MUIB)
    • The sign-off chain is formalized, but long: we'll need to have a common decision on a muon geometry within the group a few weeks in advance of the CMS-wide sign-off

Muon Alignment: Strategy

  • “Quasi-static” alignment state
    • Even when a requested sign-off date is announced in advance,

slippage can make the actual date uncertain

    • To avoid being caught without an agreed-upon geometry, will aim to

always have a “state-of-the-art" at hand

    • The discrepancies/problems that we're working on are usually motivated by the results of validation anyway: having a validated working point formalizes that (and can help assess priorities)
  • Documentation!
    • So far largely underused muon alignment Twiki
    • Aim to document results, validations, tools periodically
    • Keep documentation updated with respect to “state-of-the-art”

Muon Alignment (quick) Status

  • Full barrel alignment
    • All DTs aligned simultaneously
    • using optical (barrel+link) system
    • Good agreement of TK-MU relation
    • between HW and tracks
    • Decent agreement between track-based
    • and HW constants
      • discrepancies under study
    • First combined HW+track-based
    • alignments
    • Validated by PVT
  • Improved internal DT alignment
    • Includes theta superlayer
    • Includes all corner-block-to-wires
    • and quality control measurements





  • CSC alignment
    • New beam-halo + photogrammetry alignment
    • New optical alignment in r-f coordinates
    • Combined Endcap + Link information
    • Next step: integration of optical + track-based
    • alignments

Track-Based Alignment Status I

  • Unexpected dependence of residuals on position within the chamber (“sawtooth effect”) and on track curvature are now both explained:
    • Due to a typo, RPC hits were allowed to bias tracker-to-muon propagation
    • With this corrected, many long-standing mysteries have been resolved
  • Consequences:
    • Can lower pT > 100 GeV/c cut used in alignment (see next slide)
    • Must revise resolution vs. integrated luminosity estimates (“5-20 pb-1 for 200 microns” derived from affected code, likely to be too optimistic)

Track-Based Alignment Status II

Residuals are now wider but mean is independent of Pt:

can align without high Pt cut

removing the rpc hit bias

Track-Based Alignment III

Removing the RPC-hit bias
  • Both of these effects had the same cause
  • All barrel residuals distributions now behave ~ as expected; new alignment produced

Muon Alignment: HW vs Tracks

  • Chamber-to-chamber agreement at the level of 1.3mm
    • Outliers in these TB-HW rf difference plots are low-statistics chambers
  • Largest remaining discrepancy: trend vs. wheel in local-x
  • Independent of RPC-hit bias
  • Simple twist model already ruled out by Link and Global and SA track constrains
  • Other possibilities under study

Muon Alignment: ongoing studies

  • Track-based analysis:
    • Confirmed at the level of raw residuals: no sharp breaks at chamber boundaries indicates either a track bias or a coherent rotation of the superplanes
    • Not proportional to station number, as would be expected of rotated tracks (effect is clearly constant with respect to station number)
  • Hardware analysis:
    • End-to-end difference measured by link: 1.1 +- 0.6 mm, not 4 mm as it appears from tracks
    • Inclinometers and transfer lines can provide additional independent cross-checks
  • Using independence of the TB/HW datasets to find remaining problems and converge upon a solution

Alignment Constants Time-line











Agree on common HW runs @ 3.8T




CSC tracks

BH, cosmics, pp

Tools for

HW Automation

Endcap X,Y ME2,3,4

DT tracks

Cosmics, pp



AR vs. TK

Endcap Z, fx


Endcap T.L.


Optimize HW+Track


Integrated HW Geom @ 3.8T

Validated HW alignment

Validated track alignment

Integrated HW + track-based Geom

Validated Muon Alignment Geometry

Enter “quasi-static” loop (with faster turn-around)

New alignment constants due ~ here ?