[PWGEM] PhotonMeson: Add task for event normalization on derived data

- If only events with a certain number of photons (or any other kind of selection) are stored in the derived data, the table "PMEvSelBits" in the event selection task can store the event selection bits. Hence, the number of selected events before the specific selection on the number of photons etc. can be retrieved.
- This new task just loops over these event-selection bits and stores them in a histogram.
- For future: Also store it as a function of multiplicity etc.

Author: jokonig

PWGEM/PhotonMeson/Tasks/CMakeLists.txt

@@ -190,3 +190,8 @@ o2physics_add_dpl_workflow(emcal-mc-task
                     SOURCES emcalMcTask.cxx
                     PUBLIC_LINK_LIBRARIES O2::Framework O2Physics::AnalysisCore O2Physics::PWGEMPhotonMesonCore
                     COMPONENT_NAME Analysis)
+
+o2physics_add_dpl_workflow(event-normalization-task
+                    SOURCES eventNormalizationTask.cxx
+                    PUBLIC_LINK_LIBRARIES O2::Framework O2Physics::AnalysisCore
+                    COMPONENT_NAME Analysis)

PWGEM/PhotonMeson/Tasks/eventNormalizationTask.cxx

@@ -0,0 +1,81 @@
+// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+/// \file eventNormalizationTask.cxx
+/// \brief task to produce histogram with event counter information
+/// \author Joshua Konig, joshua.konig@cern.ch
+
+#include "PWGEM/PhotonMeson/DataModel/EventTables.h"
+
+#include <Framework/AnalysisDataModel.h>
+#include <Framework/AnalysisTask.h>
+#include <Framework/HistogramRegistry.h>
+#include <Framework/HistogramSpec.h>
+#include <Framework/InitContext.h>
+#include <Framework/runDataProcessing.h>
+
+#include <TH1D.h>
+
+#include <string_view>
+
+using namespace o2;
+using namespace o2::aod;
+using namespace o2::framework;
+using namespace o2::framework::expressions;
+using namespace o2::soa;
+
+struct EventNormalizationTask {
+
+  HistogramRegistry fRegistry{"output", {}, OutputObjHandlingPolicy::AnalysisObject, false, false};
+
+  void init(InitContext& /*context*/)
+  {
+    // Names derived from EventAcceptance bits in EventTables.h
+    std::vector<std::string> vecLabelNames = {
+      "all",
+      "has MC coll",
+      "good zVtx",
+      "is FT0AND",
+      "No TFB",
+      "ITS ROFB",
+      "Same bunch Pileup",
+      "ZVtxFT0PV",
+      "No coll in time range",
+      "good track occi",
+      "Good FT0 occupancy",
+      "kTVXinEMC",
+      "Good centrality",
+      "Good RCT",
+      "Good Sel8"};
+    fRegistry.add("EventNormalization/hEventCounter", "Event Counter;category;#it{N}_{evt}", kTH1D, {{static_cast<int>(vecLabelNames.size()), -0.5, -0.5 + static_cast<int>(vecLabelNames.size())}}, false);
+    for (size_t i = 0; i < vecLabelNames.size(); ++i) {
+      fRegistry.get<TH1>(HIST("EventNormalization/hEventCounter"))->GetXaxis()->SetBinLabel(i + 1, vecLabelNames[i].c_str());
+    }
+  }
+
+  // Process function only takes the entries and fills them into the histogram. This is done per DF and not per collision
+  void processNorm(o2::aod::PMEvSelBit const& evSelBit)
+  {
+
+    auto vecEvSelBits = evSelBit.eventSelectionBit();
+    for (size_t i = 0; i < vecEvSelBits.size(); ++i) {
+      fRegistry.fill(HIST("EventNormalization/hEventCounter"), i, vecEvSelBits[i]);
+    }
+  }
+
+  PROCESS_SWITCH(EventNormalizationTask, processNorm, "run event normalization task", true);
+};
+
+WorkflowSpec defineDataProcessing(ConfigContext const& context)
+{
+  return WorkflowSpec{
+    adaptAnalysisTask<EventNormalizationTask>(context, TaskName{"event-normalization-task"})};
+}