Nikolai Smirnov has proposed to add 3 % CF₄ to TPC gas mixture  in order to reduce transverse diffusion.
This requires adding 110 V to Anode Voltage in order to compensate the gas gain amplification loss.
The goal is to improve momentum resolution and Upsilon mass width in order to provide STAR with possibility to separate Upsilon, Upsilon' and (may be also) Upsilon" states.
The results of garfield++ calculation for different gas mixture has been presented at  

https://drupal.star.bnl.gov/STAR/blog/fisyak/diffusions-and-drift-velocity-garfield-calculations-p10-and-arch4cf4-gas-mixtures

For STAR TPC at electric field intensity 135 V/cm transverse diffusion in 87% at + 10 % CH₄ + 3 % CF₄ is reduced from 220 μm / sqrt(cm) for P10 to 121 μm /sqrt(cm) i.e. it is reduced by a factor ~2.

Rongrong Ma gives measured width of Upsilon from Run 14+16:   224 MeV/c².
 
The plot below is from the MTD proposal with Y(1S) mass width of about 140 MeV/c². 

I have check width of Upsilon' => μ+ μ- with simulation  using configurations old TPC (2016), iTPC (2019), iTPC with adding 3 %CF4  (2022). The  invariant mass plots are show below.
1. 2016, old TPC:  width = 128 MeV/c²
2. 2019, iTPC, width = 95 MeV/c²
3. 2022, iTPC + CF₄, width = 81 MeV/c²

The question and conclusions:
1. It is not clear why MC width from MC is 40% narrower than from RC. It should be studied.
2. TPC => iTPC gives improvement in Upsilon' mass resolution ~25%
3. iTPC => CF₄ iTPC gives another improvement 15%.
4. Total TPC => CF₄ iTPC gives 37%