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Upgraded track extrapolator for VSI

Matthew Gignac requested to merge matthewgignac/athena:fix-ip-extrapolator into 21.0


This merge request implements a new track extrapolator in the VSI algorithm (generic secondary vertexing algorithm used for BSM searches and using large radius tracking). Several analysis groups have reported a phi-asymmetry of attached tracks to the secondary vertex, specifically for tracks with large d0 values. The new extrapolator significantly reduces the phi-asymmetry, and includes a better estimation of track parameter uncertainties (which are used when calculating the SV IP significance). The changes are implemented such that the original extrapolator can be turned back on by configuring with TrkExtrapolator. The default configuration points to the new and improved extrapolator.

Link to presentation from Giulia:

Tagging @cohm, @leejr , @gripelli, @jstupak, @hoide , @kpachal, @spagan, @mdanning , @npetters

Cheers, Matthew

Edited by Matthew Gignac

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