feat: split B0 from central detector tracking

[wdconinc]

Briefly, what does this PR introduce?

There is no way a relevant track can have both hits in the forward endcaps and the B0 tracker. We can therefore separate the tracking of both, and by doing so gain in the combinatoric search space and allow for parallelization.

This PR splits the B0 tracker seeding and tracking from the central detector seeding and tracking. After separate tracking, the tracks are merged again in the ReconstructedChargedWithoutPIDParticles collection.

What kind of change does this PR introduce?

• Bug fix (issue #__)
• New feature (issue #__)
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No.

Does this PR change default behavior?

No.

[simonge]

Ideally would this happen after the PID or even cluster matching as none of the tracks should be able to match the central PID or calorimeter detectors?

One thing this change could adversely effect is the important contribution of the B0 to vertexing.

[wdconinc]

One thing this change could adversely effect is the important contribution of the B0 to vertexing.

The B0 tracks are recombined with central tracks before we do vertexing.

[simonge]

One thing this change could adversely effect is the important contribution of the B0 to vertexing.

The B0 tracks are recombined with central tracks before we do vertexing.

Do you not need to combine the Central and B0 CKFActsTrajectories when passed into the iterative vertex finder?

https://github.com/eic/EICrecon/pull/1744/files#diff-e093c4fb16d0a0c3255aa88be403f9ea77ce7ac00a8120f47b34c8de55b30bd9L232-L238

[github-actions]

Capybara summary for PR 1744

• rec_dis_10x100_minQ2=0_craterlake
• rec_dis_10x100_minQ2=1000_craterlake_tracking_only
• rec_dis_18x275_minQ2=0_craterlake_18x275
• rec_dis_18x275_minQ2=1000_craterlake_18x275
• rec_dis_5x41_minQ2=0_craterlake_5x41
• rec_e_1GeV_20GeV_craterlake
• rec_pi_1GeV_20GeV_craterlake
  ^{_{Last updated 2025-04-23T18:02-04:00 0536a97}}

[simonge]

Do you not need to combine the Central and B0 CKFActsTrajectories when passed into the iterative vertex finder?

Yeah, and that's hard. Showstopper for now.

Is creating a collection which adds both vectors of trajectories not as simple with Acts internal types? Would it instead be possible to make the iterative vertex finder input variadic and pass both collections.

[wdconinc]

Do you not need to combine the Central and B0 CKFActsTrajectories when passed into the iterative vertex finder?

Yeah, and that's hard. Showstopper for now.

Is creating a collection which adds both vectors of trajectories not as simple with Acts internal types? Would it instead be possible to make the iterative vertex finder input variadic and pass both collections.

Variadic doesn't work since only one Acts::TrackContainer has to be passed as input. We'd need to create a new container and add all tracks one by one.

[wdconinc]

The number of tracks now found in the B0 chain is consistent with the decrease in the Central chain.