A starting point for an important topic...

Based on Offline QA Issue 10014, I decided to to see what evidence was around for asymmetric TPC SpaceCharge & GridLeak in Run 14 AuAu data.

signedDCAs from run 15077036 (AuAu200)

I asked Zhao Feng and Zhengqiao Zhang about their data used in determining the initial SC & GL calibrations, and was able to make the following plots of sc vs. zdcx for AuAu200 and AuAu15 respectively, where red is east-only tracks, blue is west-only tracks, and black is all tracks (not shown on AuAu15):

In AuAu200, there is clearly a luminosity-dependent splitting of the SpaceCharge, higher in the east than west. In this AuAu15 data, there is splitting, but it is higher in the west, and does not show any notable luminosity dependence. So, for now, I will focus on AuAu200.

Some other plots from Offline QA that may help understand, but I think the signs point to a background source of positively charged global tracks which is at z ~= -40 to -20 cm.

Vertex z distribution:

Global track z-DCA to beam axis distribution (just different scales):

Negative and positive charge track counts for globals (first) and primaries (second):

-Gene