Add utility function to calculate tracks momentum

src/cpp/CMakeLists.txt

@@ -120,6 +120,7 @@ SET( LCIO_UTIL_SRCS
   ./src/UTIL/PIDHandler.cc
   ./src/UTIL/ILDConf.cc
   ./src/UTIL/ProcessFlag.cc
+  ./src/UTIL/TrackTools.cc
 )
 
 SET( LCIO_MT_SRCS

src/cpp/include/UTIL/TrackTools.h

@@ -0,0 +1,15 @@
+#ifndef UTIL_TrackTools_H
+#define UTIL_TrackTools_H 1
+
+#include "EVENT/Track.h"
+#include <array>
+
+namespace UTIL{
+    /** Extract track momentum from its track parameters and magnetic field
+    * @author Bohdan Dudar
+    * @version August 2022
+    */
+    std::array<double, 3> getTrackMomentum(const EVENT::Track* track, double bz);
+}
+
+#endif

src/cpp/src/UTIL/TrackTools.cc

@@ -0,0 +1,17 @@
+#include "UTIL/TrackTools.h"
+#include <cmath>
+
+namespace UTIL{
+    std::array<double, 3> getTrackMomentum(const EVENT::Track* track, double bz){
+        std::array<double, 3> mom;
+        double omega = track->getOmega();
+        double phi = track->getPhi();
+        double tanL = track->getTanLambda();
+        double c_light = 299.792458; // mm/ns
+        double pt = (1e-6 * c_light * bz) / std::abs(omega);
+        mom[0] = pt*std::cos(phi);
+        mom[1] = pt*std::sin(phi);    
+        mom[2] = pt*tanL;
+        return mom;
+    }
+}