add per-step kinematics ntuple ("Steps") to ROOT output

Adds a second ntuple alongside the existing "Hits" ntuple with one row
per Geant4 step. Records event_id, track_id, step_no, PDG code, and
pre/post position + kinetic energy for every step in the simulation.

Also extends run_batch() with return_steps=False; when True, returns
(hits_mf, steps_mf) instead of just hits_mf.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bind/G4Calo.py

@@ -334,7 +334,8 @@ def run_batch(
         maxEnergy_GeV: float = -1.0,
         filename: str = "",
         no_mp: bool = False,
-        manual_seed : int = -1):
+        manual_seed : int = -1,
+        return_steps: bool = False):
     """
 Run a full Geant4 simulation batch with automatic parallelisation.
 
@@ -361,12 +362,17 @@ no_mp : bool, optional
     Disable multiprocessing (run single-threaded) for debugging.
 manual_seed : int, optional
     Optional random seed. If < 0, seeds are generated automatically.
+return_steps : bool, optional
+    If True, also return a MiniFrame of step-level data (one row per
+    Geant4 step across all events). Returns a tuple (hits, steps).
 
 Returns
 -------
-MiniFrame
-    Table-like structure with one row per event, containing both scalar
-    values and fixed-size sensor arrays.
+MiniFrame or tuple[MiniFrame, MiniFrame]
+    If return_steps is False (default): event-level MiniFrame with one
+    row per event. If return_steps is True: (hits, steps) where steps
+    has one row per Geant4 step with columns event_id, track_id,
+    step_no, pdg, pre_x/y/z, pre_E, post_x/y/z, post_E.
 
 Notes
 -----
@@ -463,6 +469,9 @@ Example
             if os.path.exists(f):
                 os.remove(f)
     print('G4Calo: concatenation finished after {:.2f} seconds'.format(sw.elapsed()))
+    if return_steps:
+        steps_df = _assemble_results_to_mini_df(rp, tree_name="Steps")
+        return df, steps_df
     return df
 
 def _fill_event(gd : GeometryDescriptor, 

src/RunAction.cc

@@ -80,7 +80,22 @@ RunAction::RunAction()
   analysisManager->CreateNtupleIColumn("sensor_layer",hitLayer);
   analysisManager->CreateNtupleIColumn("sensor_copy_number",hitCopyNumber);
 
+  analysisManager->FinishNtuple();
 
+  // Steps ntuple (one row per step, ntuple id=1)
+  analysisManager->CreateNtuple("Steps", "Steps");
+  analysisManager->CreateNtupleIColumn("event_id");   // col 0
+  analysisManager->CreateNtupleIColumn("track_id");   // col 1
+  analysisManager->CreateNtupleIColumn("step_no");    // col 2
+  analysisManager->CreateNtupleIColumn("pdg");        // col 3
+  analysisManager->CreateNtupleDColumn("pre_x");      // col 4
+  analysisManager->CreateNtupleDColumn("pre_y");      // col 5
+  analysisManager->CreateNtupleDColumn("pre_z");      // col 6
+  analysisManager->CreateNtupleDColumn("pre_E");      // col 7
+  analysisManager->CreateNtupleDColumn("post_x");     // col 8
+  analysisManager->CreateNtupleDColumn("post_y");     // col 9
+  analysisManager->CreateNtupleDColumn("post_z");     // col 10
+  analysisManager->CreateNtupleDColumn("post_E");     // col 11
   analysisManager->FinishNtuple();
 }
 

src/SteppingAction.cc

@@ -33,6 +33,9 @@
 
 #include "G4Step.hh"
 #include "G4RunManager.hh"
+#include "G4AnalysisManager.hh"
+#include "G4Track.hh"
+#include "G4ParticleDefinition.hh"
 
 using namespace B4;
 
@@ -68,16 +71,31 @@ void SteppingAction::UserSteppingAction(const G4Step* step)
 
   
   auto sensor = DetectorConstruction::getDetectorConstruction()->getGeometryDescriptor()->getSensorByVolume(volume);
-  if(sensor == nullptr){
-    //can simply be not an active volume, so no need to throw an error
-    //G4cout << "Sensor not found in" << volume->GetName() << G4endl; //DEBUG
-    return;
+  if(sensor != nullptr){
+    //G4cout << "Sensor found in " << volume->GetName() << " with copy number " << volume->GetCopyNo()<< G4endl; //DEBUG
+    sensor->energy += edep;
   }
-  //G4cout << "Sensor found in " << volume->GetName() << " with copy number " << volume->GetCopyNo()<< G4endl; //DEBUG
-  sensor->energy += edep;
-  //find sensor by volume copy number
 
+  // Record step kinematics for every step
+  auto analysisManager = G4AnalysisManager::Instance();
+  auto pre   = step->GetPreStepPoint();
+  auto post  = step->GetPostStepPoint();
+  auto track = step->GetTrack();
+  int evtId  = G4RunManager::GetRunManager()->GetCurrentEvent()->GetEventID();
 
+  analysisManager->FillNtupleIColumn(1, 0, evtId);
+  analysisManager->FillNtupleIColumn(1, 1, track->GetTrackID());
+  analysisManager->FillNtupleIColumn(1, 2, track->GetCurrentStepNumber());
+  analysisManager->FillNtupleIColumn(1, 3, track->GetDefinition()->GetPDGEncoding());
+  analysisManager->FillNtupleDColumn(1, 4, pre->GetPosition().x());
+  analysisManager->FillNtupleDColumn(1, 5, pre->GetPosition().y());
+  analysisManager->FillNtupleDColumn(1, 6, pre->GetPosition().z());
+  analysisManager->FillNtupleDColumn(1, 7, pre->GetKineticEnergy());
+  analysisManager->FillNtupleDColumn(1, 8, post->GetPosition().x());
+  analysisManager->FillNtupleDColumn(1, 9, post->GetPosition().y());
+  analysisManager->FillNtupleDColumn(1, 10, post->GetPosition().z());
+  analysisManager->FillNtupleDColumn(1, 11, post->GetKineticEnergy());
+  analysisManager->AddNtupleRow(1);
 }
 
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