STAR Flow, Chirality and Vorticity PWG

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

Hi, Jamie and all,

On this particular point....

On Apr 26, 2022, at 7:53 PM, James Dunlop via Star-fcv-l <star-fcv-l AT lists.bnl.gov> wrote:

The beam shifts by ~40 um all the time.  It's beam steering at that level,
often used to level our luminosity.

I offer the following not as a contradiction, but as complementary information on the beam positions (and I'm certainly not making any kind of statement on noticeable impacts from beam positions on track reconstruction efficiency)...

The mean <Vx> at z=0 for each fill (which I labeled as "x0") is shown in the below plot obtained from only a small fraction of the event statistics. The colors show the two beam species. I would conclude that whatever beam steering they were doing, they managed to get x0 consistent within a given species to within +/-15 microns fill-to-fill. If it weren't for that consistency, we wouldn't see the apparent offset between the two species.

But on the core topic of this thread of tracking efficiency differences between the two species, I do not have the confidence to say that SpaceCharge & GridLeak distortion corrections are consistent between the two species at the level necessary to avoid systematic track reconstruction efficiency differences at the 0.1% level. That level of confidence would be difficult to achieve, in my opinion.

-Gene