[PWGUD] Add some cuts (AliceO2Group#11076)

Co-authored-by: rabbit <rabbit@hole>

Author: zhaomr13

PWGUD/Tasks/flowCorrelationsUpc.cxx

@@ -225,8 +225,17 @@ struct FlowCorrelationsUpc {
 
   void processSame(UDCollisionsFull::iterator const& collision, UdTracksFull const& tracks)
   {
+    if (std::abs(collision.posZ()) > cfgZVtxCut) {
+      return;
+    }
+    if (tracks.size() < cfgMinMult || tracks.size() > cfgMaxMult) {
+      return;
+    }
+
     int gapSide = collision.gapSide();
-    if (gapSide < 0 || gapSide > 2) {
+    const int minGapSide = 0;
+    const int maxGapSide = 2;
+    if (gapSide < minGapSide || gapSide > maxGapSide) {
       return;
     }