[PWGJE] PWGJE - fix jetBackgroundAnalysis RC without 2 leading jets (#9628)

Author: aimeric-landou

PWGJE/Tasks/jetBackgroundAnalysis.cxx

@@ -173,21 +173,22 @@ struct JetBackgroundAnalysisTask {
         }
       }
     }
-
     registry.fill(HIST("h2_centrality_rhorandomconewithoutleadingjet"), collision.centrality(), randomConePt - M_PI * randomConeR * randomConeR * collision.rho());
 
     // randomised eta,phi for tracks, to assess part of fluctuations coming from statistically independently emitted particles, removing tracks from 2 leading jets
     double randomConePtWithoutOneLeadJet = 0;
     double randomConePtWithoutTwoLeadJet = 0;
-    for (auto const& track : tracks) {
-      if (jetderiveddatautilities::selectTrack(track, trackSelection)) {
-        float dPhi = RecoDecay::constrainAngle(randomNumber.Uniform(0.0, 2 * M_PI) - randomConePhi, static_cast<float>(-M_PI)); // ignores actual phi of track
-        float dEta = randomNumber.Uniform(trackEtaMin, trackEtaMax) - randomConeEta;                                            // ignores actual eta of track
-        if (TMath::Sqrt(dEta * dEta + dPhi * dPhi) < randomConeR) {
-          if (!trackIsInJet(track, jets.iteratorAt(0))) {
-            randomConePtWithoutOneLeadJet += track.pt();
-            if (!trackIsInJet(track, jets.iteratorAt(1))) {
-              randomConePtWithoutTwoLeadJet += track.pt();
+    if (jets.size() > 1) { // if there are no jets, or just one, in the acceptance (from the jetfinder cuts) then one cannot find 2 leading jets
+      for (auto const& track : tracks) {
+        if (jetderiveddatautilities::selectTrack(track, trackSelection)) {
+          float dPhi = RecoDecay::constrainAngle(randomNumber.Uniform(0.0, 2 * M_PI) - randomConePhi, static_cast<float>(-M_PI)); // ignores actual phi of track
+          float dEta = randomNumber.Uniform(trackEtaMin, trackEtaMax) - randomConeEta;                                            // ignores actual eta of track
+          if (TMath::Sqrt(dEta * dEta + dPhi * dPhi) < randomConeR) {
+            if (!trackIsInJet(track, jets.iteratorAt(0))) {
+              randomConePtWithoutOneLeadJet += track.pt();
+              if (!trackIsInJet(track, jets.iteratorAt(1))) {
+                randomConePtWithoutTwoLeadJet += track.pt();
+              }
             }
           }
         }