I've put together a macro that calculates the purity utilizing the output of the 'StJetTreeThirdMaker' class.  The plots below are a check to make sure everything's working.  However, the values look reasonable even with the fairly arbitrary choices of pTtrk, eTtrg, and whatnot.  The shaded regions on the delta-phi correlations indicate the region which is being used to calculate the near-side yield.  Here 'D' denotes the per-trigger yield (normalized by the no. of triggers and by the delta-phi bin size).