diff --git a/Examples/options/tut_detsim.py b/Examples/options/tut_detsim.py
index 9f9b0e766006c6ff345683ee4c68fa80871f3532..2ecb5e3f6ea15ba4ce0dd5b6f8e37b33c102c1c2 100644
--- a/Examples/options/tut_detsim.py
+++ b/Examples/options/tut_detsim.py
@@ -59,6 +59,14 @@ from Configurables import HepMCRdr
 from Configurables import GenPrinter
 
 # gun = GtGunTool("GtGunTool")
+# gun.Particles = ["pi+"]
+# gun.Energies = [100.] # GeV
+
+# gun.ThetaMins = [] # rad; 45deg
+# gun.ThetaMaxs = [] # rad; 45deg
+
+# gun.PhiMins = [] # rad; 0deg
+# gun.PhiMaxs = [] # rad; 360deg
 
 stdheprdr = StdHepRdr("StdHepRdr")
 stdheprdr.Input = "/cefs/data/stdhep/CEPC250/2fermions/E250.Pbhabha.e0.p0.whizard195/bhabha.e0.p0.00001.stdhep"
diff --git a/Generator/src/GtGunTool.cpp b/Generator/src/GtGunTool.cpp
index f9d7da9cb9f132384b34e846309fb7c9616d14d0..a8f65da3863f1622f63997fef74ebc77c36c4a05 100644
--- a/Generator/src/GtGunTool.cpp
+++ b/Generator/src/GtGunTool.cpp
@@ -87,6 +87,7 @@ GtGunTool::mutate(MyHepMC::GenEvent& event) {
         mcp.setSimulatorStatus(1);
         // mcp.setCharge();
         mcp.setTime(0.0);
+        mcp.setMass(mass);
         // mcp.setVertex(); 
         // mcp.setEndpoint();
 
@@ -123,6 +124,11 @@ GtGunTool::mutate(MyHepMC::GenEvent& event) {
                 info() << "phi is fixed: " << phimin << endmsg;
             }
         }
+
+        debug() << "Direction: "
+                << " cos(theta): " << costheta
+                << " phi: " << phi
+                << endmsg;
         
         double px = p*sintheta*cos(phi);
         double py = p*sintheta*sin(phi);