Merge pull request #42250 from sbein/from-CMSSW_13_2_X_2023-07-11-2300

Preserve electron mass after FastSim Bremsstrahlung emmision
cms-sw · Jul 14, 2023 · 018666c · 018666c
2 parents 058ca1a + 8cf798e
commit 018666c
Showing 1 changed file with 5 additions and 0 deletions.
diff --git a/FastSimulation/SimplifiedGeometryPropagator/plugins/Bremsstrahlung.cc b/FastSimulation/SimplifiedGeometryPropagator/plugins/Bremsstrahlung.cc
@@ -137,6 +137,7 @@ void fastsim::Bremsstrahlung::interact(fastsim::Particle& particle,
   // Needed to rotate photons to the lab frame
   double theta = particle.momentum().Theta();
   double phi = particle.momentum().Phi();
+  double m2dontchange = particle.momentum().mass() * particle.momentum().mass();
 
   // Calculate energy of these photons and add them to the event
   for (unsigned int i = 0; i < nPhotons; ++i) {
@@ -155,6 +156,10 @@ void fastsim::Bremsstrahlung::interact(fastsim::Particle& particle,
 
     // Update the original e+/-
     particle.momentum() -= photonMom;
+    particle.momentum().SetXYZT(particle.momentum().px(),
+                                particle.momentum().py(),
+                                particle.momentum().pz(),
+                                sqrt(pow(particle.momentum().P(), 2) + m2dontchange));
   }
 }