example config for positrons shot backwards

SimCore/exampleConfigs/backwards-positron.py

@@ -0,0 +1,40 @@
+"""fire a positron with the input energy backwards from the target
+
+This is helpful for the situation where the beam spot needs to be
+determined. Instead of doing complicated math to figure out how much
+an electron of a given energy curves, let's just use a positron and Geant4
+to do the math for us!
+
+Note
+----
+This only functions well if the detector components upstream of the target
+are not included in the simulation. (If they are, then the positron interacts
+with them easily spoiling the measurement.) This can be done by commenting
+out their inclusion in the detector.gdml with `<!-- ... -->`.
+"""
+
+from LDMX.Framework import ldmxcfg
+import argparse
+
+parser = argparse.ArgumentParser()
+parser.add_argument('--n-events', type=int, default=10, help='number of events to simulate')
+parser.add_argument('--beam', type=float, required=True, help='beam energy in GeV')
+
+args = parser.parse_args()
+
+p = ldmxcfg.Process("beam")
+p.maxEvents = args.n_events
+p.termLogLevel = 1
+p.run = 1
+p.outputFiles = [ f'backwards_positron_beam_{args.beam}.root' ]
+
+from LDMX.SimCore import generators
+from LDMX.SimCore import simulator
+import LDMX.Ecal.EcalGeometry
+import LDMX.Hcal.HcalGeometry
+
+mySim = simulator.simulator( "mySim" )
+mySim.setDetector( 'ldmx-det-v14' , True )
+mySim.generators = [ generators.single_backwards_positron(args.beam) ]
+mySim.description = 'Basic test Simulation'
+p.sequence = [ mySim ]