HOWTO run a single-particle-gun simulation

Running a single particle Gun

In this example we are going to use hdgeant4 and we are simulating a single particle eta to be generated. The eta is chosen to also show how to force geant to let eta decay only into one final state rather than all possible ones. To achieve all this we require two files:

1. "control.in", to define the kinematics and with the particle type. An example of this files looks as follows:
   TRIG 1000
   KINE 117 5.97 0.01 0. 0.0 0.05 360.
   SCAP 0. 0. 1.
   TGTWIDTH 0.5 .5
   HADR 1
   OUTFILE 'etaRAND.hddm'
   RNDM 2057859
   RUNG 30402
2. "r.mac", this file contains the necessary commands to run hdgeant4 and also sets up the decay modes for the eta as follows, in this example decay mode 1 is given 100% (3pi0 decay) all other decay modes are zero and 1000 events are generated:
   /particle/select eta
   /particle/property/decay/select 0
   /particle/property/decay/br 0
   /particle/property/decay/select 1
   /particle/property/decay/br 1
   /particle/property/decay/select 2
   /particle/property/decay/br 0
   /particle/property/decay/select 3
   /particle/property/decay/br 0
   /run/beamOn 1000
3. run this as follows:
   hdgeant4 r.mac
   and will create a file etaRAND.hddm as specified in the control.in file.