Provide tools & setup for tracking of Heavy Ion on ITk events in standalone ACTS environment

[tboldagh]

The goal is to work out tools & setup to demonstrates ACTS tracking chain on for Heavy Ion events in ATLAS ITk detector. In comparison to an existing chain the HI reconstruction is likely to need fast vertex z estimation and a modification to the seeding that would allow to contain the seeds to that vertex only. (Default chain should be obviously tried first to obtain reference.) The project is covered by Petr Bolek.

A concrete work items are:

• review existing vertex Z finders
• implement the vertex Z finder in ACTS
• consider implementations suitable for accelerators (not the 1st priority)
• implement example algorithm using it
• extend the functionality of the seed finder to also accept z vertex constraint (not only beam spot position & mag field as is now)
• optimise setup
• consider adding plugin to hijing generator - only if particle gun will be deemed insufficient for testing - coordinate with @plariono who works on ALICE on it
• integrate the solution with Athena

[tboldagh]

ATLAS implementation in trigger can be found here: https://gitlab.cern.ch/atlas/athena/-/blob/master/Trigger/TrigTools/IDScanZFinder/src/IDScanZFinderInternal.h

[tboldagh]

And let me tag FI: @noemina @toyamaza @asalzburger

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[paulgessinger]

@tboldagh is there a plan for this?

[tboldagh]

Yes, Petr got some preliminary results with z finder algorithm. Should be presented soon.

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[pbalek]

Hi all, I think PR #2038 is in a good shape. I tuned the parameters for Pb+Pb collisions, so it runs quite fast while it has a good resolution.

Now, we can skip some phi a z bins. That needs to be set as a parameter of the tool. Ideally, the tool could decide itself but let's keep that for the next version. Also, I added some iterations, so some fraction of the worst planes/rays can be discarded each pass.

As of now, the tool is not used anywhere. However, I've seen #2195, so once that is merged, I think we can utilize the seed vertex finder there.

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[tboldagh]

There is an interesting evolution of this project. Updates to be seen soon.