I looked into the mean transverse momentum for pions and jets in each of my z bins. First, here’s a comparison of data (black points) and Monte Carlo (red lines) for the BJP1 trigger:

It looks good to me, so I went on to compare simulations for jet patch and minimum-bias triggers:

In hindsight, this plot makes perfect sense — the trigger hardens the pT spectrum for the jets, so each JP z bin (which integrates over 10-25 GeV) has a higher average jet p_{T} than the MB version.

Now, this 3 GeV p_{T} shift means that we’re biasing the sample in each z bin towards higher x. This is almost certainly the source of the observed trigger bias in the Monte Carlo asymmetries for π+. So, what’s the next step?