Alignment open issues and tasks

This is an incomplete list of open issues in detector alignment. Please add whatever you think is missing. Or assign yourself to a task.

Stripping for alignment

We would like to have a set of dedicated dsts with tracks suitable for alignment. The best would be to create a selection for the stripping. We want to select events with

  • high momentum tracks, e.g. tracks above 20 GeV
  • tracks through velo overlap regions. Use the VeloTrackSelector.
  • velo halo tracks. Use the TrackSelector, or eventually VeloTrackSelector
  • tracks through IT overlap regions. Use the ITTrackSelector.
  • clean J/psis
  • clean Ks
  • unbiased selected muon tracks of high momentum (use muon-stand alone track reconstruction)

Some of these are already in the express stream. The Ks dst probably exist, but I don't know how clean it is.

To speed up the processing of these events, it would be useful to store the tracks in a separate Track container. I don't know if that is possible in the stripping.

Who: ?

Date entered: 2010-05-17

Tool to display differences between databases

We would like to have a tool to display the difference between alignment databases.

Who: Christophe, Albert ?

Date entered: 2010-05-17

Field-on / field-off difference in T station alignment

The alignment constants extracted with field-on and field-off data are not compatible with each other and also not compatible with survey, in particular in the first T stations. Part of the problem is the alignment in 'z': movements in z of several mm are obtained with respect to the survey. These movements are not physical and have lead to a severe curvature bias, which was at some point wrongly attributed to the field. However, even if those z movements are fixed, the field-on and field-off alignment are not compatible. A futher complication here is the internal alignment of IT: the z-position and rotations of the layers inside an IT box are actually not that well constrained.

For a brief overview, see the first few slides of this talk.

To solve this issue several studies have been proposed, a.o. * align the detector with very high momentum tracks (e.g. > 30 GeV). * revive the RASNIK system to get a handle on the true momevents between field-on and field-off

Who: everybody smile

Date entered: 2010-05-17

Velo-TT to T matching

There are significant biases left in the matching of Velo-TT to T segments are seen by the TrckFitMatchMonitor. See e.g. slide 4 of this talk.

This is probably just another symptom of the lack in understanding of field-on and field-off alignment.

TT scaling problem

Even after fixing the pitch there are still some remaining problems with scaling in TT. See recent talks by Christophe.

Who: Christophe, ...

Date entered: 2010-05-17

OT/IT alignment versus time

The OT and IT have been opened several times, in the wintershutdown but also at least once this spring. We need to know how stable the alignment is.


Date entered: 2010-05-18

Ks mass studies, J/psi mass studies

Study invariant mass as function of kinematic, such as

  • phi, Matt's phi: azimuthal asymmetries
  • eta, momentum: material
  • p(pi+) - p(pi-): q/p bias

These studies would greatly benefit from a dst with a clean selection.

Track-Calo alignment

There is a known displacements of a few (up to 7?) mm of the ECAL C-side with respect to the tracker. See e.g. slide 9 of this talk. Olivier Deschamps thinks that 7mm is not physical.

Who: ?

Date entered: 2010-05-17

Strange tail in residual distribution of hits in Velo overlap regions

See slide 16-19 of this talk.

Note that there is a real problem in simulation as well.

Who: David

Date entered: 2010-05-17

-- WouterHulsbergen - 17-May-2010

This topic: LHCb > WebHome > LHCbComputing > LHCbDetectorAlignment > AlignmentOpenIssues
Topic revision: r5 - 2010-05-21 - WouterHulsbergen
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