STAR QA Board

["Ke, Hongwei" <kehw@bnl.gov>]

Hi Geary and Gene,

L4 still uses a VPD calibration table generated Feb 2021. I do not know how good it is to the current pp run.

For the primary vertex reconstruction of L4, it Is basically the average position of DCA points of associated tracks.

It is biased toward the beam line in x-y plane, but no real constrain.

The algorithm only select one primary vertex and it is biased toward the candidate with the most associated tracks.

Best regards,

Hongwei Ke

On Dec 27, 2021, at 9:08 PM, Van Buren, Gene via STAR-QAboard-l <star-qaboard-l@lists.bnl.gov> wrote:

Hi, Geary

We have FastOffline _with_ the BeamLine constraint. The result of that is the data that was shown earlier in this thread, though it essentially showed the two components of the two different BeamLine constraints.

Then we have data I processed _without_ any BeamLine constraint. That's what my (Vtx_z,tpc - Vtpx_z,vpd) plot was made from, and the attached Vy vs. Vx plot is made from.

Hope that helps,

-Gene

<PastedGraphic-3.png>

On Dec 27, 2021, at 5:58 PM, Geary Eppley <eppley@rice.edu> wrote:

Hi Gene:

Thanks. The offset matches L4 which does VPD-TPC gets -2. The RMS is also about the same as L4 and about the same as Run 17.

If I understand the earlier emails, you use fast offline with modified parameters to get this data.

Do you have a Vx vs Vy plot for this data?

-Geary

Quoting "Van Buren, Gene" <gene@bnl.gov>:

Hi, Geary

On Dec 27, 2021, at 1:02 PM, Geary Eppley <eppley@rice.edu<mailto:eppley@rice.edu>> wrote:
The central Vx vs Vy central distribution shown Friday has a radius of order 1mm. The L4 distribution has a radius of order 1 cm. Do you know what causes that difference?

I do not know exactly what L4 is doing, but my best guess is that they are using no BeamLine constraint at all.


We are interested in VPD-TPC Vz offset to see if any adjustments need to be made. L4 consistently shows and offset of -2 cm or less. The RMS is just slightly worse than Run 17, which is not bad considering the current problems with the active splitter.

What offset do you see in your analysis?


I'm attaching a histogram of (Vtx_z,tpc - Vtpx_z,vpd) from the data I used to determine the BeamLine last Tuesday. Hope that's useful.

-Gene

[cid:5FA1EB5A-4C18-43E5-B139-E2BF69938FDB@attlocal.net]

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