Star-tpc-l mailing list

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

Hi, TPC-ers

My initial findings on this urgent topic using prompt hits in 5000 events 
from Run 19 3.85 GeV FXT....

- Irakli's calibration of dependence on EPD max TAC (earlier time hit) may be 
reasonably determined in terms of the coefficient (slope) of the correlation 
with TPC T0. There are two other factors I haven't yet investigated: any 
overall offsets, and the spread (how tight is the correlation).

- Irakli's code loops over EPD hits to find the one with the max TAC, but my 
code uses the StTriggerData class with its functions: 
xxxEarliestTDC(StBeamDirection), where the direction is either east or west, 
and xxx is in (vpd,epd,bbc,zdc). I have yet to investigate the difference 
between them, but it's on my to-do list.

- Irakli's code doesn't care whether the EPD hit is from the east or west 
EPD. In FXT data, the max TAC he finds is essentially always in the west 
(makes sense as the west is closer to the collision).

- Irakli finds an EPD west timing that he calls valid in about 99% of events, 
but over 10% of those events have a TAC that is "0" despite being "valid", 
which isn't really valid for a T0 correction calculation (the timer hit its 
maximum time?). This must contribute to a smearing, but only for ~10% of 
events.

- My code sees a much higher efficiency of valid times from EPD east (~80%) 
than EPD west (~15%), and a good correlation with the east, so it may be 
better to restrict to using the east side EPD hits than the west? I'm not 
sure why I have such a lower west side efficiency than Irakli (~90%, see 
previous point).

- I see a valid BBC east time in essentially all events (nearly 100% 
efficiency), though BBC west is only ~10% efficient. At the very least, the 
BBC east is a good backup for when there is no valid EPD time. I would need 
to look into whether BBC east is better than EPD east even when there is a 
valid EPD east time.

Comments are welcome. Thanks,
-Gene.

> On Jul 13, 2023, at 11:55 AM, Richard Witt via Star-tpc-l 
> <star-tpc-l AT lists.bnl.gov> wrote:
> 
>       — Tommy estimated SC from files
>               — also compared PV reconstruction from east and west 
> individually, there is a difference
>               — plots are attached to previous TPC meeting agenda
>               — Yuri believes the result is an overestimated efficiency
>               — may be a reproduction of 2019 and 2020 FXT, Gene may try to 
> reproduce the calibration to remove the problem
>               — problem will still exist in P21ib
>               — Gene will look into comparing with work previously done by 
> Irakli
>                       — if there is a difference we may need to include the 
> correction for the reproduction