Star-tpc-l mailing list

["Van Buren, Gene" <gene AT bnl.gov>]

Thanks for the additional plot, Zach. My notes are below, and I welcome any 
correction/supplementation to my logic as I'm left confused by a few things 
...

> On Jul 25, 2024, at 3:25 PM, Zachary Sweger <star-tpc-l AT lists.bnl.gov> 
> wrote:
> 
> My edited slides from today are here: 
> https://drupal.star.bnl.gov/STAR/system/files/24_07_25%20Update_v1.pdf
> 
> I added my analysis track cuts on slide 2. And I added the mean(mean(eta)) 
> plot as a function of Vz on slide 21.


1) I think a track of eta around 1.2 is *mostly* a west track. It's the west 
part of the track that probably dominates its projection to the vertex z 
position.

2) From what I can tell, the peaks in the <<eta>> distributions (slide 21) 
align with the peaks in the vertex counts (slide 37), which implies that 
vertices reconstructed just off the z peaks are even more biased towards 
lower eta (west-only) tracks. This is true in both productions. Not really 
sure what to conclude from this.

3) The two peaks do not appear to be east-track-dominated vertices vs. 
west-track-dominated vertices, as I exapect their <<eta>> would need to be 
much more different than they are for that to be true. Good!

4) What is the true position of the fixed target? One would suppose from 
slide 37 that the peak at smaller z is the triggered peak (many more counts). 
Its shift therefore is likely due to the new TPC alignment (and/or T0) of the 
*west* TPC half.

5) This implies that the secondary peak (higher z) is at the same z position 
in both productions by coincidence, shifted back to that position after 
alignment+T0 by some other effect different between the two productions.

6) If west tracks determine vertex z, the secondary peak being offset from 
the first by about half a cm higher in z makes sense in the P24ia production 
if it's truly from beam from the *prior* RHIC bucket (*early* tracks in west 
reconstruct at higher z). This could probably be confirmed by some of the 
trigger group's data (might be able to "see" beam in the prior buckets).

7) ....But that leaves an open question of why the two peaks are less than 
half a cm apart in the test production...?

8) Another mystery about the secondary peak is why its <<eta>> shifts by a 
greater amount than the primary peak's <<eta>> does....?

9) Resolving track-breaking should improve the number of high-eta tracks, but 
the test production appears to have a slight bias (compared to P24ia) towards 
low-eta primary tracks. Could this hypothetically be explained by improved 
low-eta efficiency as well as high-eta? Simple eta distribution plots might 
clarify.

Thanks,
-Gene