This fixes #8

core/include/PECReader.hpp

@@ -259,7 +259,13 @@ class PECReader
          */
         bool BuildAndSelectEvent();
 
-        /// Calculate event weights (including systematics)
+        /**
+         * \brief Calculate event weights (including systematics)
+         * 
+         * The method is called for both simulation and real data. However, only trigger weight is
+         * evaluated in the latter case; it is needed to allow an additional event selection via
+         * TriggerRange::PassEventSelection.
+         */
         void CalculateEventWeights();
 
         /// Stores particles from the hard interaction in hardParticles collection

core/src/PECReader.cpp

@@ -678,10 +678,21 @@ bool PECReader::BuildAndSelectEvent()
 
 void PECReader::CalculateEventWeights()
 {
-    // Calculate different components of an event weight
+    // Calculate weight due to trigger selection. This is the only event weight that can make
+    //sense for real data (e.g. if there is an additional selection specified in a TriggerRange
+    //object). However, with real data this weight is either 0. or 1.
     double const weightTrigger = (triggerSelection) ? triggerSelection->GetWeight(*this) : 1.;
 
+    if (not dataset.IsMC())
+    {
+        // Don't forget to update the central weight
+        weightCentral = weightTrigger;
+
+        return;
+    }
+
 
+    // Reweighting for the pile-up
     WeightPileUpInterface::Weights weightPileUp;
 
     if (puReweighter)
@@ -690,6 +701,7 @@ void PECReader::CalculateEventWeights()
         weightPileUp.Set(1., 1., 1.);
 
 
+    // Reweighting for b-tagging
     double const weightBTagging =
      (bTagReweighter) ? bTagReweighter->CalcWeight(goodJets, WeightBTag::Variation::Central) : 1.;