1.  For each pion pair, the outgoing parton closest to the pion pair in eta,phi space(separation distance is dR) with dR<0.5 is the associated parton (line 7 or 8 from pythia).  The distribution of the distance between pion pair and associated parton is in figure 1.  The ratio of the matched pairs/total pairs at this step is in figure 4. 
2.  If the parton from the polarized proton (line 5 or 6) is a quark and the parton from 1) is also a quark, then use the x from the polarized proton.
3.  Get the average x for quarks for xF>0 and xF<0 and each pT bin.  See figure 2.  The old plot with dR<0.5 on the wrong dR distribution is now figure 3 to show the data points hardly move. 

Figure 1: Distribution of separation of pion pair and closest outgoing parton in eta,phi space.

Figure 2:  average x vs pT for xF>0 and xF<0, where a cut on the distance between the pion pion and the associated parton was applied(dR<0.5).

Figure 3:  average x vs pT for xF>0 and xF<0, where a cut on the distance between the pion pion and the associated parton was applied(dR<0.5) (wrong dR distribution!!!)

Figure 4:  The number of pion pairs matched to an associated outgoing parton with dR < 0.5 divided by the total number of pairs as a function of pT.