[PWGEM] add option for at least one photon in Dalitz Skimmer (#17996)

Co-authored-by: Laura Gansbartl <lgansbartl@pcikf5.ikf.uni-frankfurt.de>

Author: lgansbartl

PWGEM/PhotonMeson/TableProducer/skimmerPrimaryElectronFromDalitzEE.h

@@ -166,6 +166,7 @@ struct skimmerPrimaryElectronFromDalitzEE {
   Configurable<float> maxMee{"maxMee", 0.5, "max. mee to store dalitz ee pairs"};
   Configurable<float> minMeegamma{"minMeegamma", 0.3, "min. mee to store eegamma candidates"};
   Configurable<float> maxMeegamma{"maxMeegamma", 0.8, "max. mee to store eegamma candidates"};
+  Configurable<bool> photonsNeeded{"photonsNeeded", true, "require a minimum of one photons per collision"};
   Configurable<bool> fillLS{"fillLS", true, "flag to fill LS histograms for QA"};
   Configurable<int> fillingMode{"fillingMode", 1, "Filling mode| 1: fill tracks without pair selection, 2: fill tracks from selected pairs, 3: fill tracks from selected pairs that can be combined with a photon"};
   Configurable<bool> fillWithEtaMassCut{"fillWithEtaMassCut", true, "only valid for fillingmode 3; true: filling tabled based on eta candidate selection with minMeegamma < M < maxMeegamma, false: fill identical to fillingmode 2"};
@@ -745,6 +746,10 @@ struct skimmerPrimaryElectronFromDalitzEE {
       auto varFillingMode = static_cast<enumFillingMode>(fillingMode.value);
 
       const auto& v0photons_per_coll = v0photons.sliceBy(perCol_pcm, collision.globalIndex());
+      if (photonsNeeded && v0photons_per_coll.size() == 0) {
+        continue;
+      }
+
       const auto& posTracks_per_coll = posTracks->sliceByCached(o2::aod::track::collisionId, collision.globalIndex(), cache);
       const auto& negTracks_per_coll = negTracks->sliceByCached(o2::aod::track::collisionId, collision.globalIndex(), cache);
       const auto& slicedTracks = tracks.sliceBy(perTracksCollision, collision.globalIndex());
@@ -927,6 +932,10 @@ struct skimmerPrimaryElectronFromDalitzEE {
       auto varFillingMode = static_cast<enumFillingMode>(fillingMode.value);
 
       const auto& v0photons_per_coll = v0photons.sliceBy(perCol_pcm, collision.globalIndex());
+      if (photonsNeeded && v0photons_per_coll.size() == 0) {
+        continue;
+      }
+
       const auto& posTracks_per_coll = posTracksMC->sliceByCached(o2::aod::track::collisionId, collision.globalIndex(), cache);
       const auto& negTracks_per_coll = negTracksMC->sliceByCached(o2::aod::track::collisionId, collision.globalIndex(), cache);
       const auto& slicedTracks = tracks.sliceBy(perTracksCollision, collision.globalIndex());