[PWGCF] add kIsGoodZvtxFT0vsPV flag in MC (#12689)

Author: Luzhiyongg

PWGCF/Flow/Tasks/flowMc.cxx

@@ -87,6 +87,7 @@ struct FlowMc {
   O2_DEFINE_CONFIGURABLE(cfgRecoEvSel8, bool, false, "require sel8 for reconstruction events")
   O2_DEFINE_CONFIGURABLE(cfgRecoEvkIsGoodITSLayersAll, bool, false, "require kIsGoodITSLayersAll for reconstruction events")
   O2_DEFINE_CONFIGURABLE(cfgRecoEvkNoSameBunchPileup, bool, false, "require kNoSameBunchPileup for reconstruction events")
+  O2_DEFINE_CONFIGURABLE(cfgEvSelkIsGoodZvtxFT0vsPV, bool, false, "removes collisions with large differences between z of PV by tracks and z of PV from FT0 A-C time difference, use this cut at low multiplicities with caution")
   Configurable<std::vector<double>> cfgTrackDensityP0{"cfgTrackDensityP0", std::vector<double>{0.6003720411, 0.6152630970, 0.6288860646, 0.6360694031, 0.6409494798, 0.6450540203, 0.6482117301, 0.6512592056, 0.6640008690, 0.6862631416, 0.7005738691, 0.7106567432, 0.7170728333}, "parameter 0 for track density efficiency correction"};
   Configurable<std::vector<double>> cfgTrackDensityP1{"cfgTrackDensityP1", std::vector<double>{-1.007592e-05, -8.932635e-06, -9.114538e-06, -1.054818e-05, -1.220212e-05, -1.312304e-05, -1.376433e-05, -1.412813e-05, -1.289562e-05, -1.050065e-05, -8.635725e-06, -7.380821e-06, -6.201250e-06}, "parameter 1 for track density efficiency correction"};
   float maxEta = 0.8;
@@ -405,6 +406,11 @@ struct FlowMc {
       // cut time intervals with dead ITS staves
       return 0;
     }
+    if (cfgEvSelkIsGoodZvtxFT0vsPV && !collision.selection_bit(o2::aod::evsel::kIsGoodZvtxFT0vsPV)) {
+      // removes collisions with large differences between z of PV by tracks and z of PV from FT0 A-C time difference
+      // use this cut at low multiplicities with caution
+      return 0;
+    }
     return 1;
   }