Star-tpc-l mailing list

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

Hi, TPC-ers

Several years ago, Irakli (and some helpers) calibrated event-by-event T0 
corrections in 2019 & 2020 FXT datasets to compensate for the long bunch 
lengths and the consequential shifts in collision event timing with respect 
to the RHIC clock that begins the TPC readout.

    https://drupal.star.bnl.gov/STAR/blog/iraklic/fxt-t0-work

I believe Yuri has expressed concerns with this correction as he brought new 
T0 calibrations jointly with his new TPC alignment. I have also previously 
identified flaws in Irakli's correction scheme, and I have prepared an 
alternative which we have been using in beam-beam data. I would like to 
advocate for the use of this alternative event-by-event T0 correction for the 
FXT datasets as well, and to that end I have used the variation in difference 
in z positions between primary vertices reconstructed by the east-only and 
west-only TPC halves:

    
https://drupal.star.bnl.gov/STAR/blog/genevb/Compare-event-event-T0-performance

I do realize that this correction has only a minor impact, but the impact 
does appear to be measurable. The impact of appropriately biasing our 
vertex-finding by 2 cm vertically below the z-axis (where the target material 
sits) is much more significant.

I have only completed the calibration for my method for about half the BES-II 
FXT datasets, but it would only take me a couple days to calibrate the 
remainder if we decide to utilize it.

Thanks,
-Gene