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Seeding Plans M. Needham EPFL

Seeding Plans M. Needham EPFL. Outline. The problem How the seeding works Questions + Solutions. No solutions here, just ideas, suggestions, brainstorming of how to improve the seeding Slides are to provoke discussion/suggestions etc. What is the problem ?.

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Seeding Plans M. Needham EPFL

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  1. Seeding Plans M. Needham EPFL

  2. Outline • The problem • How the seeding works • Questions + Solutions No solutions here, just ideas, suggestions, brainstorming of how to improve the seeding Slides are to provoke discussion/suggestions etc

  3. What is the problem ? Hits are not added to the track even though we know they are there To try to account for this windows are set large [which certainly costs time if nothing else] Suggestion is that it is caused by rotations around x (alignment gives up to 30 mrad for IT boxes) How critical is this for the seeding ? We know from the introduction of the beam tilt a and the vague memories of that period that tilts around x are very important as the seeding works in projection Note rotations would also explain why in the TED ITGenericTracking we never had large problems adding hits [zero angle tracks]

  4. Hit ‘Finding’ Efficiency 2010 IT1V IT2X2 Hits in T station picked up on downstream tracks Downstream Ks M. Schiller OT1U OT3X2

  5. Reminder Roger Forty, Zurich tracking workshop 14th July 2006 Tracks found in beam tilted x-z projection. To add y, use common tilt of T stations, and calculate hyperparabolic plane of track, cut this with y measurements

  6. How the seeding works • Based on this the main strategy is to work in projection for both IT and OT • To find overlap tracks + have extra robustness 2nd pass IT algorithm based on stubs • Stub = spacepoint (X1UVX2) • Only build stubs for hits not found pass 1 • Stubs are linked to form tracks (2 or 3 stub combinations allowed) • Stubs are also extended into the OT • Stub finding ‘a bolt on’: not as well tuned for speed or efficiency as projection search

  7. How the seeding works xz tracking using (x,z) y = 0 OT x search IT x search Pass 1: Projection IT stereo search OT stereo search Assume beam tilt Stub Finding Pass 2: Spacepoints Stub Linking Likelihood Refit x-z: With beam tilt

  8. Questions + Solutions Are the rotations about x the problem ? • Corelation between low efficiency and large rotations ? (Note v good, u bad would be consistant with past studies) What is the solution… • If no common projection exists, why work in projection ? better to work in space in IT • Kludge possible: instead of beam tilt, intersect x-z track with y, tilting per layer. Is dydz layer available (to be fast) ? Does this make any sense ? Try and see… • Refit - can be done correctly [either case] • What is going on in the OT ?

  9. The Kludge X projection • Make windows small and add factor corresponding to size of individual box rotations, alittle messy [what to do if 2 boxes in stacks are rotated, one not] • Make window depend on track angle/momentum [to reduce size] Stereo • Instead of beam tilt, intersect x-z track with y, tilting per layer. Is dydz layer available (to be fast) ? Does this make any sense ? • Technically easy to do, but does it make sense ? x-z tracks still assumes there is a projection. Try and see

  10. Plans Fix the seeding fit so that it does not assume beam tilt Easy but only helps if we can cut afterwards on the likelihood, windows still large Try flipping the order of the projection/space searches in IT Potential gain in efficiency, if hypothesis correct, Lose in speed but gain small windows Current stub finding not robust: approach will not well work for some detector stacks Try going to y with the box tilt in the projection search Messy may or may not work Long term dream Make robust + fast spacepoint building for IT ( was done once before + worked ) Can it replace entirely the projection approach ?

  11. Needs ? Data • How well do we know the rotations ? How well can we know them with beam tracks alone ? • Are there new requests for IT survey, Rasnik, serious IT/OT Cosmic running ? MC • To first order I will try to tune with data • It would be helpful in order to have the best tuning to have MC with misaligned IT/TT

  12. Summary • List of potential avenues to explore given • Will start to work in this direction after I return from Vertex • Clearly a critical element missed: misaligned MC • No guaranteed nice solution exists. • Working in projection will be messy in terms of search windows • Working in space will work in terms of search windows, but to be robust in terms of efficiency needs work [and is not fully guaranteed]

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