Update G4DarkBreM with configurable A' scaling and decay

.gitmodules

@@ -1,9 +1,6 @@
 [submodule "docs/doxygen.conf/doxygen-awesome-css"]
 	path = docs/doxygen.conf/doxygen-awesome-css
 	url = https://github.com/jothepro/doxygen-awesome-css
-[submodule "SimCore/G4DarkBreM"]
-	path = SimCore/G4DarkBreM
-	url = https://github.com/LDMX-Software/G4DarkBreM.git
 [submodule "Tracking/acts"]
 	path = Tracking/acts
 	url = https://github.com/acts-project/acts
@@ -13,3 +10,6 @@
 [submodule "Trigger/ruckus"]
 	path = Trigger/ruckus
 	url = https://github.com/slaclab/ruckus
+[submodule "SimCore/G4DarkBreM"]
+	path = SimCore/G4DarkBreM
+	url = https://github.com/LDMX-Software/G4DarkBreM.git

Biasing/python/eat.py

@@ -165,7 +165,10 @@ def midshower_dimuon( detector , generator, bias_factor , bias_threshold , min_d
     return sim
 
 
-def dark_brem( ap_mass , lhe, detector, generator) :
+def dark_brem(ap_mass, db_event_lib, detector, generator, 
+              scale_APrime = False, decay_mode = 'no_decay',
+              ap_tau = -1.0, dist_decay_min = 0.0,
+              dist_decay_max = 1.0) :
     """Example configuration for producing dark brem interactions in the ECal. 
 
     This configures the simulator to fire a 4 GeV electron upstream of the 
@@ -177,14 +180,24 @@ def dark_brem( ap_mass , lhe, detector, generator) :
     ----------
     ap_mass : float
         The mass of the A' in MeV.
-    lhe : str
+    db_event_lib : str
         The path to the reference library to use as vertices of the dark brem. 
     detector : str
         Path to the detector.
     generator : simcfg.PrimaryGenerator
         Beam generator for this simulation which should be a ParticleGun
         so we can configure the PrimaryToEcalFilter to select events where
         beam electrons retain 87.5% of their energy.
+    scale_APrime : bool
+        Whether to scale the A' momentum along with the recoil electron.
+    decay_mode : str
+        The A' decay mode. Either no_decay, flat_decay, or geant_decay
+    ap_tau : float
+        The A' decay lifetime in seconds
+    dist_decay_min : float
+        The minimum lab-frame distance at which to decay the A'
+    dist_decay_max : float
+        The maximum lab-frame distance at which to decay the A'
 
     Return
     ------
@@ -213,9 +226,14 @@ def dark_brem( ap_mass , lhe, detector, generator) :
 
     #Activiate dark bremming with a certain A' mass and LHE library
     from LDMX.SimCore import dark_brem
-    db_model = dark_brem.G4DarkBreMModel( lhe )
+    db_model = dark_brem.G4DarkBreMModel( db_event_lib )
     db_model.threshold = 0.5*generator.energy #GeV - minimum energy electron needs to have to dark brem
     db_model.epsilon   = 0.01 #decrease epsilon from one to help with Geant4 biasing calculations
+    db_model.scale_APrime = scale_APrime
+    db_model.decay_mode = decay_mode
+    db_model.ap_tau = ap_tau
+    db_model.dist_decay_min = dist_decay_min
+    db_model.dist_decay_max = dist_decay_max
     sim.dark_brem.activate( ap_mass , db_model )
 
     #Biasing dark brem up inside of the ecal volumes
@@ -229,6 +247,7 @@ def dark_brem( ap_mass , lhe, detector, generator) :
 
     beam_energy = generator.energy*1000
     sim.actions = [
+            util.DecayChildrenKeeper([622]), # keep children of A' decay
             util.PartialEnergySorter(0.5*beam_energy),
             filters.PrimaryToEcalFilter(0.875*beam_energy),
             filters.EcalDarkBremFilter(0.5*beam_energy)

SimCore/src/SimCore/APrimePhysics.cxx

@@ -45,15 +45,32 @@ APrimePhysics::APrimePhysics(const framework::config::Parameters& params)
 }
 
 void APrimePhysics::ConstructParticle() {
+  auto model{parameters_.getParameter<framework::config::Parameters>("model")};
+  static const std::map<std::string, G4APrime::DecayMode> decay_lut = {
+      {"no_decay", G4APrime::DecayMode::NoDecay},
+      {"flat_decay", G4APrime::DecayMode::FlatDecay},
+      {"geant_decay", G4APrime::DecayMode::GeantDecay}};
+  auto decay_it{decay_lut.find(
+      model.getParameter<std::string>("decay_mode", "no_decay"))};
+  if (decay_it == decay_lut.end()) {
+    EXCEPTION_RAISE(
+        "BadConf",
+        "Unrecognized decay mode '" +
+            model.getParameter<std::string>("decay_mode") +
+            "',"
+            " options are 'no_decay', 'flat_decay', or 'geant_decay'.");
+  }
+
+  double ap_tau = model.getParameter<double>("ap_tau", -1.0);
+
   /**
    * Insert A-prime into the Geant4 particle table.
-   * For now we flag it as stable.
    *
    * Geant4 registers all instances derived from G4ParticleDefinition and
    * deletes them at the end of the run. We configure the A' to have
    * the input mass and the PDG ID number of 622.
    */
-  G4APrime::Initialize(ap_mass_, 622);
+  G4APrime::Initialize(ap_mass_, 622, ap_tau, decay_it->second);
 }
 
 void APrimePhysics::ConstructProcess() {
@@ -88,7 +105,14 @@ void APrimePhysics::ConstructProcess() {
                        always DB off electrons here */
               ,
               model.getParameter<double>("threshold"),
-              model.getParameter<double>("epsilon"), scaling_method_it->second),
+              model.getParameter<double>("epsilon"), scaling_method_it->second,
+              g4db::G4DarkBreMModel::XsecMethod::Auto,
+              model.getParameter<double>("max_R_for_full", 50.0),
+              model.getParameter<int>("aprime_lhe_id", 622),
+              true,  // always load the library
+              model.getParameter<bool>("scale_APrime", false),
+              model.getParameter<double>("dist_decay_min", 0.0),
+              model.getParameter<double>("dist_decay_max", 1.0)),
           parameters_.getParameter<bool>("only_one_per_event"),
           1., /* global bias - should use bias operator instead */
           parameters_.getParameter<bool>("cache_xsec"));