Star-tpc-l mailing list

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

Hi, all

As noted at today's TPC meeting, on the topic of track projections to ETOF 
showing displacements, I decided to look at track residuals in the TPC in the 
Run 20 FXT data. I have now posted plots and added some observations on my 
blog page here:

https://drupal.star.bnl.gov/STAR/blog/genevb/Residuals-Run-20-FXT

As a brief summary, I do see non-zero mean residuals near the east endcap, 
foremost at the level of ~2 mm in the z direction for primary tracks at small 
radii. The residuals shown here cannot be due to the proposed ideas of fringe 
magnetic field effects, nor energy loss in materials, that could potentially 
account for the track projection displacements at ETOF. But it is also 
unclear to me whether 2 mm in this region of the TPC (whatever the cause may 
be) can project to several cm at the position of the ETOF.

Food for thought. Comments and suggestions welcome.

-Gene

p.s. There are other observable effects consistent with what the PWG analyses 
and embedding studies have reported at the central membrane and at very small 
radii on the east side.