Way back, I fit the Pythia8 recoil jet spectra for pi0 and gamma-direct triggers with power laws.  This was to get a reasonable prior to use as a systematic in our unfolding procedure.  Unfortunately, I only did the cases for 9 - 11 GeV and 11 - 15 GeV:

https://drupal.star.bnl.gov/STAR/blog/dmawxc/update-09212018-pythia-fitting-pi0-and-gamma-direct-spectra-power-laws

So here are the fits for the 15 - 20 GeV pi0 case.  I followed the 3rd procedure from the above post: the recoil jet spectrum was fit with a power law from 2 GeV/c to the upper limit of the trigger pT range (20 GeV/c).  Since statistics were kinda rough, I did it for two different binning schemes: one with 1 GeV/c bins and one with 2 GeV/c bins.  As you can see below, only the overall normalization changes.  The fit powers are consistent between the two cases.