sPHENIX tracking discussion

["Osborn, Joseph" <josborn1 AT bnl.gov>]

Hi all, and adding the tracking list for further comments others might have,

Here are a few comments from the tracking side of things.

1. The seeding algorithm uses wide search windows right now to try to ensure that we get some correlation between the silicon. These windows were blown up based on the previous MVTX ideal geometry, where there was significant layer to layer rotation (i.e. the ideal geometry was wrong compared to how the MVTX was actually constructed). That rotation has now been implemented to reduce the residuals, so these windows likely need to be re-tuned.
2. The silicon seeding algorithm creates (at a minimum) triplets in the 5 layers. In our simulation, we deploy this algorithm in the MVTX to reduce the presence of duplicates. In the real data, with the misalignment, we found we could not find anything in the MVTX alone (again, before the rotation alignment fix), so we expanded the seeding algorithm to search in the MVTX+INTT. This means you likely get a nontrivial background of fake tracks where 2 layers of the MVTX match to a single layer in the INTT.
3. Silicon seeds should not be considered as real tracks. We need to make some basic quality criteria to reduce the presence of background, mismatches, etc. One of these that we have been using in alignment studies is that the track must have 5 measurements on it, for exactly this reason.

I'm happy to chat about this more. The track reconstruction is going to continuously need to be optimized as we learn more about the alignment, backgrounds, timing correlation between the silicon subsystems, etc. Right now we need to make selections to have high purity at a cost of efficiency, and as we learn more about the data we will be able to re-tune these to improve the efficiency with a cost to purity.

Joe Osborn

___________________________

Joe Osborn, Ph.D

Physics Department

Brookhaven National Laboratory

josborn1 AT bnl.gov

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From: sphenix-intt-l-request AT lists.bnl.gov on behalf of Hao-Ren Jheng
Sent: Tuesday, July 9, 2024 10:28 AM
To: sphenix-intt-l AT lists.bnl.gov
Cc: Nagle, James; Joe Osborn
Subject: [[Sphenix-intt-l] ] Question about silicon seeds/INTT QA

Dear INTT group and experts (cc RC, Jamie, and tracking expert, Joe),

I have been working on the silicon seeds offline QA and have one question that requires INTT experts’ input.
We have one QA plot showing the correlation between number of MVTX clusters v.s number of INTT clusters per silicon-only track, and we are seeing a large fraction of tracks having only 1 INTT cluster (please see the attached plot).
Do you have an idea why this is the case and what could be the cause of it?

Best,
Hao-Ren