Lumonisity has been kept approximately constant throughout fills in run16. We were wondering if the space charge has a strong intensity depedence. 


Data: 

We chose fill 19651 to investigate that. 
(http://online.star.bnl.gov/RTS/plots/storedPlots.php?fill=19651&screen=plot&file=fillplots_2016/all_groups_tpc_19651.png)

Data produced by Gene for runs:
17067005
17067006
17067010
17067013
17067016
have been used.
The data is at: /star/subsys/tpc/SCGL/genevb/AuAu200_2016/MUDST/
Chain: P2016,btof,BEmcChkStat,pxlhit,isthit,ssthit,NoPxlIT,NoIstIT,NoSstIT,CorrX,OSpaceZ2,OGridLeak3D,-hitfilt


Events Selection:

I used MB triggers: 520021, 520022, 520023. 
|V_z| < 5cm  &&  |V_z - VzVpd| < 3.0 cm  && gRefMult > 30 (to have reasonable vertex precision). 
Vertex with highest number of tracks && correlation to VPD has been used. 

Tracks:
Global tracks, |dca| < 3.0, nFit >= 20, nFit/nMax > 0.52, match to TOF. 


The following are the mean and sigma of guassian fits to the DCA peak between -0.5 to 0.5 cm. 




We note the following:

1. The intensity dependence is within of a couple a hundred microns, if any. Not significant.
2. There is charge dependence (~0.05cm split) of DCA mean. 
3. The worse sigma on the east side is likely due to the poor performance of sector 20.
4. Current space charge has a ~0.05cm offset for low pT tracks?

-- Mustafa

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We also looked at the DCA_Z to check T0: 


There is a significant T0 offset.