diff --git a/MC/config/PWGGAJE/external/generator/generator_pythia8_gaptrigger_jets_hook.C b/MC/config/PWGGAJE/external/generator/generator_pythia8_gaptrigger_jets_hook.C
new file mode 100644
index 000000000..33ac86d92
--- /dev/null
+++ b/MC/config/PWGGAJE/external/generator/generator_pythia8_gaptrigger_jets_hook.C
@@ -0,0 +1,268 @@
+R__ADD_INCLUDE_PATH($O2DPG_MC_CONFIG_ROOT)
+///#include "FairGenerator.h"
+//#include "Generators/GeneratorPythia8.h"
+#include "Pythia8/Pythia.h"
+#include "MC/config/PWGGAJE/hooks/jets_hook.C"
+//#include "TRandom.h"
+//#include <fairlogger/Logger.h>
+//
+//#include <string>
+//#include <vector>
+
+// Jet-jet custom event generator
+// that alternates between 2 gun generators. 
+// set up to inject MB events alongside jet-jet events
+// in 'MB-gap' mode.
+// The number of MB events injected, and the PYTHIA config
+// for each event type is defined by the user in the .ini 
+// generator file (e.g. GeneratorJE_gapgen5_hook.ini)
+//
+// Author: Jaime Norman (jaime.norman@cern.ch)
+
+// o2-sim-dpl-eventgen --nEvents 10 --generator external --configKeyValues "GeneratorExternal.fileName=generator_pythia8_gaptrigger_jets_pythiabase.C;GeneratorExternal.funcName=getGeneratorPythia8GapGenJE()"
+
+namespace o2
+{
+namespace eventgen
+{
+
+using namespace Pythia8;
+
+
+/// A very simple gap generator alternating between 2 different particle guns
+class GeneratorPythia8GapGenJE : public o2::eventgen::GeneratorPythia8
+{
+public:
+  /// default constructor
+  GeneratorPythia8GapGenJE(int inputTriggerRatio = 5,std::string pathMB = "",std::string pathSignal = "") {
+
+    mGeneratedEvents = 0;
+    mInverseTriggerRatio = inputTriggerRatio;
+
+    auto seed = (gRandom->TRandom::GetSeed() % 900000000);
+
+    cout << "Initalizing extra PYTHIA object used to generate min-bias events..." << endl;
+    TString pathconfigMB = gSystem->ExpandPathName(TString(pathMB));
+    pythiaObjectMinimumBias.readFile(pathconfigMB.Data());
+    pythiaObjectMinimumBias.readString("Random:setSeed on");
+    pythiaObjectMinimumBias.readString("Random:seed " + std::to_string(seed));
+    pythiaObjectMinimumBias.init();
+    cout << "Initalization complete" << endl;
+    cout << "Initalizing extra PYTHIA object used to generate signal events..." << endl;
+    TString pathconfigSignal = gSystem->ExpandPathName(TString(pathSignal));
+    pythiaObjectSignal.readFile(pathconfigSignal.Data());
+    pythiaObjectSignal.readString("Random:setSeed on");
+    pythiaObjectSignal.readString("Random:seed " + std::to_string(seed));
+    // load jet hook to ensure at least one jet is within detector acceptance
+    Pythia8::UserHooks *hook = pythia8_userhooks_jets();
+    pythiaObjectSignal.setUserHooksPtr(std::shared_ptr<Pythia8::UserHooks>(hook));
+    pythiaObjectSignal.init();
+    cout << "Initalization complete" << endl;
+    // Add Sub generators
+    addSubGenerator(0, "MB generator");
+    addSubGenerator(1, "jet-jet generator");
+  }
+
+
+  ///  Destructor
+  ~GeneratorPythia8GapGenJE() = default;
+
+  void setUsedSeed(unsigned int seed)
+  {
+    mUsedSeed = seed;
+  };
+  unsigned int getUsedSeed() const
+  {
+    return mUsedSeed;
+  };
+
+  bool generateEvent() override
+  {
+
+    // Simple straightforward check to alternate generators
+    mPythia.event.reset();
+
+    if (mGeneratedEvents % mInverseTriggerRatio == 0) {
+      LOG(info) << "Event " <<  mGeneratedEvents << ", generate signal event";
+      // Generate event of interest
+      Bool_t mGenerationOK = kFALSE;
+      while (!mGenerationOK) {
+        mGenerationOK = pythiaObjectSignal.next();
+      }
+      mPythia.event = pythiaObjectSignal.event;
+      setEventHeaderProperties(pythiaObjectSignal);
+      LOG(info) << "--- Print info properties custom...";
+      printEventHeaderProperties(pythiaObjectSignal);
+      notifySubGenerator(1);
+    } 
+    else {
+      LOG(info) << "Event " <<  mGeneratedEvents << ", generate mb event";
+      // Generate minimum-bias event
+      Bool_t mGenerationOK = kFALSE;
+      while (!mGenerationOK) {
+        mGenerationOK = pythiaObjectMinimumBias.next();
+      }
+      mPythia.event = pythiaObjectMinimumBias.event;
+      setEventHeaderProperties(pythiaObjectMinimumBias);
+      LOG(info) << "--- Print info properties custom...";
+      printEventHeaderProperties(pythiaObjectMinimumBias);
+      notifySubGenerator(0);
+    }
+    mGeneratedEvents++;
+    return true;
+  }
+
+  // for testing
+  void printEventHeaderProperties (Pythia8::Pythia &pythiaObject) {
+    LOG(info) << "Info name = " << pythiaObject.info.name();
+    LOG(info) << "Info code = " << pythiaObject.info.code();
+    LOG(info) << "Info weight = " << pythiaObject.info.weight();
+    LOG(info) << "Info id1pdf = " << pythiaObject.info.id1pdf();
+    LOG(info) << "Info id2pdf = " << pythiaObject.info.id2pdf();
+
+    LOG(info) << "Info x1pdf = " << pythiaObject.info.x1pdf();
+    LOG(info) << "Info x2pdf = " << pythiaObject.info.x2pdf();
+    LOG(info) << "Info QFac = " << pythiaObject.info.QFac();
+    LOG(info) << "Info pdf1 = " << pythiaObject.info.pdf1();
+    LOG(info) << "Info pdf2 = " << pythiaObject.info.pdf2();
+
+    // Set cross section
+    LOG(info) << "Info sigmaGen = " << pythiaObject.info.sigmaGen();
+    LOG(info) << "Info sigmaErr = " << pythiaObject.info.sigmaErr();
+
+
+    // Set event scale and nMPI
+    LOG(info) << "Info QRen = " << pythiaObject.info.QRen();
+    LOG(info) << "Info nMPI = " << pythiaObject.info.nMPI();
+
+    // Set weights (overrides cross-section for each weight)
+    size_t iw = 0;
+    auto xsecErr = pythiaObject.info.weightContainerPtr->getTotalXsecErr();
+    for (auto w : pythiaObject.info.weightContainerPtr->getTotalXsec()) {
+      std::string post = (iw == 0 ? "" : "_" + std::to_string(iw));
+      LOG(info) << "Info weight by index = " << pythiaObject.info.weightValueByIndex(iw);
+      iw++;
+    }
+
+  }
+
+  // in order to save the event weight we need to override the following function
+  // from the inherited o2::eventgen::GeneratorPythia8 class. The event header properties
+  // are created as members of this class, and are set using the active event generator
+  // (MB or jet-jet), then propagated to the event header
+  void updateHeader(o2::dataformats::MCEventHeader* eventHeader) override {
+    /** update header **/
+    using Key = o2::dataformats::MCInfoKeys;
+
+    eventHeader->putInfo<std::string>(Key::generator, "pythia8");
+    eventHeader->putInfo<int>(Key::generatorVersion, PYTHIA_VERSION_INTEGER);
+    eventHeader->putInfo<std::string>(Key::processName, name);
+    eventHeader->putInfo<int>(Key::processCode, code);
+    eventHeader->putInfo<float>(Key::weight, weight);
+
+    // Set PDF information
+    eventHeader->putInfo<int>(Key::pdfParton1Id, id1pdf);
+    eventHeader->putInfo<int>(Key::pdfParton2Id, id2pdf);
+    eventHeader->putInfo<float>(Key::pdfX1, x1pdf);
+    eventHeader->putInfo<float>(Key::pdfX2, x2pdf);
+    eventHeader->putInfo<float>(Key::pdfScale, QFac);
+    eventHeader->putInfo<float>(Key::pdfXF1, pdf1);
+    eventHeader->putInfo<float>(Key::pdfXF2, pdf2);
+
+    // Set cross section
+    eventHeader->putInfo<float>(Key::xSection, sigmaGen * 1e9);
+    eventHeader->putInfo<float>(Key::xSectionError, sigmaErr * 1e9);
+
+    // Set event scale and nMPI
+    eventHeader->putInfo<float>(Key::eventScale, QRen);
+    eventHeader->putInfo<int>(Key::mpi, nMPI);
+    LOG(info) << "--- updated header weight = " << weight;
+
+    // The following is also set in the base class updateHeader function
+    // but as far as I can tell, there is no Xsec weight in the default
+    // header so this is not copied over for now
+
+    //size_t iw = 0;
+    //auto xsecErr = info.weightContainerPtr->getTotalXsecErr();
+    //for (auto w : info.weightContainerPtr->getTotalXsec()) {
+    //  std::string post = (iw == 0 ? "" : "_" + std::to_string(iw));
+    //  eventHeader->putInfo<float>(Key::weight + post, info.weightValueByIndex(iw));
+    //  eventHeader->putInfo<float>(Key::xSection + post, w * 1e9);
+    //  eventHeader->putInfo<float>(Key::xSectionError + post, xsecErr[iw] * 1e9);
+    //  iw++;
+    //}
+  }
+
+  void setEventHeaderProperties (Pythia8::Pythia &pythiaObject) {
+
+    auto& info = pythiaObject.info;
+
+    name = info.name();
+    code = info.code();
+    weight = info.weight();
+    // Set PDF information
+    id1pdf = info.id1pdf();
+    id2pdf = info.id2pdf();
+    x1pdf = info.x1pdf();
+    x2pdf = info.x2pdf();
+    QFac = info.QFac();
+    pdf1 = info.pdf1();
+    pdf2 = info.pdf2();
+    // Set cross section
+    sigmaGen = info.sigmaGen();
+    sigmaErr = info.sigmaErr();
+    // Set event scale and nMPI
+    QRen = info.QRen();
+    nMPI = info.nMPI();
+  }
+
+private:
+  // Interface to override import particles
+  Pythia8::Event mOutputEvent;
+
+  // Properties of selection
+  unsigned int mUsedSeed;
+
+  // Control gap-triggering
+  unsigned long long mGeneratedEvents;
+  int mInverseTriggerRatio;
+
+  // Handling generators
+  Pythia8::Pythia pythiaObjectMinimumBias;
+  Pythia8::Pythia pythiaObjectSignal;
+
+  // header info - needed to save event properties 
+  std::string  name;
+  int  code;
+  float  weight;
+  // PDF information
+  int  id1pdf;
+  int  id2pdf;
+  float  x1pdf;
+  float  x2pdf;
+  float  QFac;
+  float  pdf1;
+  float  pdf2;
+  // cross section
+  float  sigmaGen;
+  float  sigmaErr;
+  // event scale and nMPI
+  float  QRen;
+  int  nMPI;
+
+};
+
+} // namespace eventgen
+} // namespace o2
+
+/** generator instance and settings **/
+
+FairGenerator* getGeneratorPythia8GapGenJE(int inputTriggerRatio = 5, std::string pathMB = "",std::string pathSignal = "") {
+  auto myGen = new o2::eventgen::GeneratorPythia8GapGenJE(inputTriggerRatio, pathMB, pathSignal);
+  auto seed = (gRandom->TRandom::GetSeed() % 900000000);
+  myGen->setUsedSeed(seed);
+  myGen->readString("Random:setSeed on");
+  myGen->readString("Random:seed " + std::to_string(seed));
+  myGen->readString("HardQCD:all = on");
+  return myGen;
+}
diff --git a/MC/config/PWGGAJE/ini/GeneratorJE_gapgen5_hook.ini b/MC/config/PWGGAJE/ini/GeneratorJE_gapgen5_hook.ini
new file mode 100644
index 000000000..769b934c7
--- /dev/null
+++ b/MC/config/PWGGAJE/ini/GeneratorJE_gapgen5_hook.ini
@@ -0,0 +1,5 @@
+### jet-jet production with MB Gap 5
+### The external generator derives from GeneratorPythia8.
+[GeneratorExternal]
+fileName = ${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGGAJE/external/generator/generator_pythia8_gaptrigger_jets_hook.C
+funcName = getGeneratorPythia8GapGenJE(5,"${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGGAJE/pythia8/generator/pythia8_minbias.cfg","${O2DPG_MC_CONFIG_ROOT}/MC/config/PWGGAJE/pythia8/generator/pythia8_jet.cfg")
diff --git a/MC/config/PWGGAJE/ini/tests/GeneratorJE_gapgen5_hook.C b/MC/config/PWGGAJE/ini/tests/GeneratorJE_gapgen5_hook.C
new file mode 100644
index 000000000..5ac7f5173
--- /dev/null
+++ b/MC/config/PWGGAJE/ini/tests/GeneratorJE_gapgen5_hook.C
@@ -0,0 +1,71 @@
+int External() {
+    std::string path{"o2sim_Kine.root"};
+
+    float ratioTrigger = 1./5; // one event triggered out of 5
+
+
+    TFile file(path.c_str(), "READ");
+    if (file.IsZombie()) {
+        std::cerr << "Cannot open ROOT file " << path << "\n";
+        return 1;
+    }
+
+    auto tree = (TTree *)file.Get("o2sim");
+    std::vector<o2::MCTrack> *tracks{};
+    tree->SetBranchAddress("MCTrack", &tracks);
+    o2::dataformats::MCEventHeader *eventHeader = nullptr;
+    tree->SetBranchAddress("MCEventHeader.", &eventHeader);
+
+    int nEventsMB{}, nEventsJetJet{};
+    float sumWeightsMB{}, sumWeightsJetJet{};
+    int sumTracks{};
+    auto nEvents = tree->GetEntries();
+
+    for (int i = 0; i < nEvents; i++) {
+        tree->GetEntry(i);
+
+        // check subgenerator information and event weights
+        if (eventHeader->hasInfo(o2::mcgenid::GeneratorProperty::SUBGENERATORID)) {
+            bool isValid = false;
+            int subGeneratorId = eventHeader->getInfo<int>(o2::mcgenid::GeneratorProperty::SUBGENERATORID, isValid);
+            if (eventHeader->hasInfo(o2::dataformats::MCInfoKeys::weight)) {
+                float weight = eventHeader->getInfo<float>(o2::dataformats::MCInfoKeys::weight,isValid);
+                if (subGeneratorId == 0) {
+                    nEventsMB++;
+                    sumWeightsMB += weight;
+                } 
+                else if (subGeneratorId == 1) {
+                    nEventsJetJet++;
+                    sumWeightsJetJet += weight;
+                }
+            }
+        }
+        sumTracks += tracks->size();
+    }
+
+    std::cout << "--------------------------------\n";
+    std::cout << "# Events: " << nEvents << "\n";
+    std::cout << "# MB events: " << nEventsMB << "\n";
+    std::cout << "  sum of weights for MB events: " << sumWeightsMB << "\n";
+    std::cout << "# Jet-jet events " << nEventsJetJet << "\n";
+    std::cout << "  sum of weights jet-jet events: " << sumWeightsJetJet << "\n";
+    std::cout << "# tracks summed over all events (jet-jet + MB): " << sumTracks << "\n";
+
+    if (nEventsMB < nEvents * (1 - ratioTrigger) * 0.95 || nEventsMB > nEvents * (1 - ratioTrigger) * 1.05) { // we put some tolerance since the number of generated events is small
+        std::cerr << "Number of generated MB events different than expected\n";
+        return 1;
+    }
+    if (nEventsJetJet < nEvents * ratioTrigger * 0.95 || nEventsJetJet > nEvents * ratioTrigger * 1.05) {
+        std::cerr << "Number of jet-jet generated events different than expected\n";
+        return 1;
+    }
+    if(nEventsMB < sumWeightsMB * 0.95 || nEventsMB > sumWeightsMB * 1.05) {
+        std::cerr << "Weights of MB events do not = 1 as expected\n";
+        return 1;
+    }
+    if(sumTracks < 1) {
+        std::cerr << "No tracks in simulated events\n";
+        return 1;
+    }
+    return 0;
+}
diff --git a/MC/config/PWGGAJE/pythia8/generator/pythia8_jet.cfg b/MC/config/PWGGAJE/pythia8/generator/pythia8_jet.cfg
new file mode 100644
index 000000000..df6772816
--- /dev/null
+++ b/MC/config/PWGGAJE/pythia8/generator/pythia8_jet.cfg
@@ -0,0 +1,20 @@
+# 2 -> 2 jet production, oversampling by pThat^4
+
+### beams 
+Beams:idA = 2212			# proton
+Beams:idB = 2212 			# proton
+Beams:eCM = 13600. 		# GeV
+
+### processes
+SoftQCD:inelastic = off
+HardQCD:all = on
+
+### decays
+ParticleDecays:limitTau0 = on
+ParticleDecays:tau0Max = 10.
+
+### phase space cuts
+PhaseSpace:pTHatMin = 5
+PhaseSpace:pTHatMax = 600
+PhaseSpace:bias2Selection = on
+PhaseSpace:bias2SelectionPow = 4
diff --git a/MC/config/PWGGAJE/pythia8/generator/pythia8_minbias.cfg b/MC/config/PWGGAJE/pythia8/generator/pythia8_minbias.cfg
new file mode 100644
index 000000000..0b12248e9
--- /dev/null
+++ b/MC/config/PWGGAJE/pythia8/generator/pythia8_minbias.cfg
@@ -0,0 +1,13 @@
+# min. bias events
+
+### beams 
+Beams:idA = 2212			# proton
+Beams:idB = 2212 			# proton
+Beams:eCM = 13600. 		# GeV
+
+### processes
+SoftQCD:inelastic = on
+
+### decays
+ParticleDecays:limitTau0 = on
+ParticleDecays:tau0Max = 10.