added constants::nucleonMass

Framework/Particles/ParticleProperties.h

@@ -23,13 +23,12 @@
 #include <iosfwd>
 #include <type_traits>
 
-#include <corsika/units/PhysicalConstants.h>
 #include <corsika/units/PhysicalUnits.h>
 
 /**
  *
  * The properties of all elementary particles is stored here. The data
- * is taken from the Pythia ParticleData.xml file.
+ * are taken from the Pythia ParticleData.xml file.
  *
  */
 

Framework/Particles/testParticles.cc

@@ -34,6 +34,8 @@ TEST_CASE("ParticleProperties", "[Particles]") {
   SECTION("Masses") {
     REQUIRE(Electron::GetMass() / (511_keV) == Approx(1));
     REQUIRE(Electron::GetMass() / GetMass(Code::Electron) == Approx(1));
+    
+    REQUIRE((Proton::GetMass() + Neutron::GetMass()) / corsika::units::constants::nucleonMass == Approx(2));
   }
 
   SECTION("Charges") {

Framework/Units/PhysicalConstants.h

@@ -61,7 +61,9 @@ namespace corsika::units::constants {
 
   // unified atomic mass unit
   constexpr quantity<mass_d> u{Rep(1.6605402e-27L) * kilogram};
-
+  
+  auto constexpr nucleonMass = 0.5 * (0.93827 + 0.93957) * 1e9 * electronvolt;
+  
   // etc.
 
 } // namespace corsika::units::constants