Added Decay in Flight generator

Generators/DIFGenerator/CMakeLists.txt

+################################################################################
+# Package: DIFGenerator
+################################################################################
+
+# Declare the package name:
+atlas_subdir( DIFGenerator )
+
+# Install files from the package:
+atlas_install_python_modules( python/*.py POST_BUILD_CMD ${ATLAS_FLAKE8} )
+

Generators/DIFGenerator/README.md

+# Decay In Flight Sampler
+
+The DIFSampler models a two-body decay.
+
+## Usage
+
+The `runG4DecayInFlight.py` file shows a default configuration.
+
+Options available through the `DIFSampler` constructor include:
+
+* daughter1_pid - The pid of the first decay particle. The default valid pids are listed [here](https://gitlab.cern.ch/atlas/athena/-/blob/master/Generators/ParticleGun/python/samplers.py#L825). (default: 11) 
+* daughter2_pid - The pid of the second decay particle. The default valid pids are listed [here](https://gitlab.cern.ch/atlas/athena/-/blob/master/Generators/ParticleGun/python/samplers.py#L825). (default: -11)
+* mother_pid - The pid of the mother particle. Only set this if you need to get the mother's pid from the mother_sampler property (default: None)
+* mother_mom - A momentum sampler representing the mother particle's momentum. (default: PG.EThetaMPhiSampler(sqrt((1 * TeV)**2 + (10 * MeV)**2),0,10*MeV,0))
+* mother_pos - A position sampler representing the mother particle's position. (default: PG.PosSampler(0,0,[-1500,0],0))
+
+The pid, momentum sampler, and position sampler of the mother particle can be modified after initialization by setting the `mother_sampler` property of the `DIFSampler`. The `mother_sampler` property should be a [ParticleSampler](https://gitlab.cern.ch/atlas/athena/-/blob/master/Generators/ParticleGun/python/samplers.py#L858).
+

Generators/DIFGenerator/python/DIFSampler.py

+#!/usr/bin/env python
+
+#TODO: exponential decay lifetime?
+
+import ParticleGun as PG
+from math import sqrt, sin, cos, acos
+from random import uniform
+from AthenaCommon.SystemOfUnits import TeV, MeV
+from AthenaCommon.PhysicalConstants import pi
+
+class DIFSampler(PG.ParticleSampler):
+    """
+    A particle gun which models 2 particle decay.
+    """
+    class particle:
+        """
+        A helper class to hold information about a particle.
+        """
+        def __init__(self,pid = None,mass = None,mom=None,theta=None,phi=None,pos=None):
+            self.pid = pid
+            if mass is None:
+                self.mass = PG.MASSES[abs(pid)]
+            else:
+                self.mass = mass
+
+            self.mom_mag = mom
+            self.theta = theta
+            self.phi = phi
+            self.pos = pos
+
+            if self.mass is not None and self.mom_mag is not None:
+                self.E = sqrt(self.mom_mag**2 + self.mass**2)
+            else:
+                self.E = None
+
+            if self.theta is not None and self.phi is not None and self.mass is not None and self.E is not None:
+                self.mom = PG.EThetaMPhiSampler(self.E,self.theta,self.mass,self.phi).shoot()
+            else:
+                self.mom = None
+
+    def __init__(self, daughter1_pid = 11, daughter2_pid = -11, mother_pid = None, mother_mom = PG.EThetaMPhiSampler(sqrt((1*TeV)**2 + (10*MeV)**2),0,10*MeV,0),mother_pos = PG.PosSampler(0,0,[-1500,0],0)):
+        self._mother_sampler = PG.ParticleSampler(mother_pid,mother_mom,mother_pos)
+
+        self.daughter1 = self.particle(daughter1_pid)
+        self.daughter2 = self.particle(daughter2_pid)
+
+    @property
+    def mother_sampler(self):
+        return self._mother_sampler
+    
+    @mother_sampler.setter
+    def mother_sampler(self,sampler):
+        if isinstance(sampler,PG.ParticleSampler) or issubclass(type(sampler),PG.ParticleSampler):
+            self._mother_sampler = sampler
+        else:
+            raise AttributeError("DIFSampler: Trying to set mother_sampler to something other than a ParticleSampler.")
+
+    def calculate_decay_p(self,m0,m1,m2):
+        return sqrt(m0**4 - (2*m0**2 * m1**2) + (m1**4) - (2*m0**2 * m2**2) - (2*m1**2 *m2**2) + (m2**4)) / (2*m0) 
+
+    def lorentz_transformation(self):
+        self.mother_mom = self.mother.mom.shoot()
+        Bx = self.mother_mom.Px() / self.mother_mom.E()
+        By = self.mother_mom.Py() / self.mother_mom.E()
+        Bz = self.mother_mom.Pz() / self.mother_mom.E()
+        self.daughter1.mom.Boost(Bx,By,Bz)
+        self.daughter2.mom.Boost(Bx,By,Bz)
+
+    def shoot(self):
+        "Mother particle decays into two daughter particles"
+        ## Shoot daughter 1 in a random direction in CM frame
+        self.daughter1.phi = uniform(0,2 * pi)
+
+        ## ensure cos(theta) is uniform from -1 to 1
+        cos_theta = uniform(-1,1)
+        self.daughter1.theta = acos(cos_theta)
+
+        self.daughter2.phi = self.daughter1.phi + pi
+        self.daughter2.theta = acos(-cos_theta)
+
+        ## The magnitude of the momentum will be equal and opposite
+        self.mother = self.mother_sampler
+        p = self.calculate_decay_p(self.mother.mom.mass(),self.daughter1.mass,self.daughter2.mass)
+
+        self.daughter1.E = sqrt(self.daughter1.mass**2 + p**2)
+        self.daughter2.E = sqrt(self.daughter2.mass**2 + p**2)
+        
+        self.daughter1.mom = PG.EThetaMPhiSampler(self.daughter1.E,self.daughter1.theta,self.daughter1.mass,self.daughter1.phi).shoot()
+        self.daughter2.mom = PG.EThetaMPhiSampler(self.daughter2.E,self.daughter2.theta,self.daughter2.mass,self.daughter2.phi).shoot()
+
+        ## boost into lab frame
+        self.lorentz_transformation()
+
+        self.mother_pos = self.mother.pos.shoot()
+        d1 = PG.SampledParticle(self.daughter1.pid,self.daughter1.mom,self.mother_pos)
+        d2 = PG.SampledParticle(self.daughter2.pid,self.daughter2.mom,self.mother_pos)
+
+        return [d1,d2]
+
+if __name__ == "__main__":
+    import matplotlib.pyplot as plt
+    import sys
+
+    show_graphs = False
+    if len(sys.argv) > 1 and sys.argv[1] == "-g":
+        show_graphs = True
+    
+    epsilon = 10**-6 #account for round off error
+
+    ## test motionless mother particle
+    mother_pid = 321 #K+
+    mother_mass = PG.MASSES[mother_pid]
+    daughter0_pid = 211 #pi+
+    daughter1_pid = 111 #pi0
+
+    ## check uniformifty of angles
+    if show_graphs:
+        cos_thetas = [[],[]]
+        thetas = [[],[]]
+        phis = [[],[]]
+    
+    n = 100
+    for i in range(n):
+        try:
+            DIFS = DIFSampler(daughter0_pid,daughter1_pid, mother_pid) # K+ -> pi+ and pi0
+            DIFS.mother_sampler.mom = PG.EThetaMPhiSampler(mother_mass,0,mother_mass,0)
+            daughters = DIFS.shoot()
+
+            mother_mom = DIFS.mother_sampler.mom.shoot()
+
+            assert daughters[0].mom.E() + daughters[1].mom.E() == mother_mass
+            assert (daughters[0].mom.E() + daughters[1].mom.E())**2 - (daughters[0].mom.P() - daughters[1].mom.P())**2 == (PG.MASSES[mother_pid])**2
+            assert abs(daughters[0].mom.P() - daughters[1].mom.P()) <= epsilon 
+            assert daughters[0].mom.Theta() - epsilon <= abs(pi - daughters[1].mom.Theta()) <= daughters[0].mom.Theta() + epsilon
+            assert abs(daughters[0].mom.Px() + daughters[1].mom.Px()) <= epsilon
+            assert abs(daughters[0].mom.Py() + daughters[1].mom.Py()) <= epsilon
+            assert abs(daughters[0].mom.Pz() + daughters[1].mom.Pz()) <= epsilon
+            assert daughters[0].pos.X() == daughters[1].pos.X() == DIFS.mother_pos.X()
+            assert daughters[0].pos.Y() == daughters[1].pos.Y() == DIFS.mother_pos.Y()
+            assert daughters[0].pos.Z() == daughters[1].pos.Z() == DIFS.mother_pos.Z()
+
+            if show_graphs:
+                cos_thetas[0].append(cos(daughters[0].mom.Theta()))
+                cos_thetas[1].append(cos(daughters[1].mom.Theta()))
+                thetas[0].append(daughters[0].mom.Theta())
+                thetas[1].append(daughters[1].mom.Theta())
+                phis[0].append(daughters[0].mom.Phi())
+                phis[1].append(daughters[1].mom.Phi())
+
+        except AssertionError:
+            print("Error on run " + str(i))
+
+            print("mother particle:")
+            print(" E = "     + str(mother_mom.E()))
+            print(" M = "     + str(mother_mom.M()))
+            print(" P = "     + str(mother_mom.P()))
+            print(" Px = "    + str(mother_mom.Px()))
+            print(" Py = "    + str(mother_mom.Py()))
+            print(" Pz = "    + str(mother_mom.Pz()))
+            print(" theta = " + str(mother_mom.Theta()))
+            print(" phi = "   + str(mother_mom.Phi()))
+            print(" x = "     + str(DIFS.mother_pos.X()))
+            print(" y = "     + str(DIFS.mother_pos.Y()))
+            print(" z = "     + str(DIFS.mother_pos.Z()))
+
+            print("daughter 0 particle:")
+            print(" E = "     + str(daughters[0].mom.E()))
+            print(" M = "     + str(daughters[0].mom.M()))
+            print(" P = "     + str(daughters[0].mom.P()))
+            print(" Px = "    + str(daughters[0].mom.Px()))
+            print(" Py = "    + str(daughters[0].mom.Py()))
+            print(" Pz = "    + str(daughters[0].mom.Pz()))
+            print(" theta = " + str(daughters[0].mom.Theta()))
+            print(" phi = "   + str(daughters[0].mom.Phi()))
+            print(" x = "     + str(daughters[0].pos.X()))
+            print(" y = "     + str(daughters[0].pos.Y()))
+            print(" z = "     + str(daughters[0].pos.Z()))
+
+            print("daughter 1 particle:")
+            print(" E = "     + str(daughters[1].mom.E()))
+            print(" M = "     + str(daughters[1].mom.M()))
+            print(" P = "     + str(daughters[1].mom.P()))
+            print(" Px = "    + str(daughters[1].mom.Px()))
+            print(" Py = "    + str(daughters[1].mom.Py()))
+            print(" Pz = "    + str(daughters[1].mom.Pz()))
+            print(" theta = " + str(daughters[1].mom.Theta()))
+            print(" phi = "   + str(daughters[1].mom.Phi()))
+            print(" x = "     + str(daughters[1].pos.X()))
+            print(" y = "     + str(daughters[1].pos.Y()))
+            print(" z = "     + str(daughters[1].pos.Z()))
+
+            raise
+
+    if show_graphs:
+        fig,axs = plt.subplots(2,3)
+        axs[0,0].hist(thetas[0])
+        axs[0,0].set_title("daughter 0: theta")
+        axs[0,1].hist(cos_thetas[1])
+        axs[0,1].set_title("daughter 0: cos(theta)")
+        axs[0,2].hist(phis[1])
+        axs[0,2].set_title("daughter 0: phi")
+        axs[1,0].hist(thetas[1])
+        axs[1,0].set_title("daughter 1: theta")
+        axs[1,1].hist(cos_thetas[0])
+        axs[1,1].set_title("daughter 1, cos(theta)")
+        axs[1,2].hist(phis[0])
+        axs[1,2].set_title("daughter 1, phi")
+        plt.show()
+
+    # test moving mother particle
+    mother_pid = 15 #tau
+    daughter0_pid = 16 #nu_tau
+    daughter1_pid = 211 #pi+-
+
+    n = 100
+    for i in range(n):
+        M = PG.MASSES[mother_pid]
+        theta = acos(uniform(-1,1))
+        mother_mom = PG.EThetaMPhiSampler([M,3*M],theta,M,[0,2*pi])
+        mother_pos = PG.PosSampler(x=0,y=0,z=[-1500,0],t=0) 
+
+        DIFS = DIFSampler(daughter0_pid,daughter1_pid,mother_pid) # tau -> nu_tau and pi+-
+        DIFS.mother_sampler = PG.ParticleSampler(pid=mother_pid,mom=mother_mom,n=1,pos=mother_pos)
+        daughters = DIFS.shoot()
+
+        try:
+            mother_mom = DIFS.mother_mom
+            s = daughters[0].mom+daughters[1].mom
+
+            assert mother_mom.E() - epsilon <= s.E() <= mother_mom.E() + epsilon
+            assert mother_mom.P() - epsilon <= s.P()<= mother_mom.P() + epsilon 
+            assert mother_mom.Px() - epsilon <= s.Px() <= mother_mom.Px() + epsilon
+            assert mother_mom.Py() - epsilon <= s.Py() <= mother_mom.Py() + epsilon
+            assert mother_mom.Pz() - epsilon <= s.Pz() <= mother_mom.Pz() + epsilon
+            assert daughters[0].pos.X() == daughters[1].pos.X() == DIFS.mother_pos.X()
+            assert daughters[0].pos.Y() == daughters[1].pos.Y() == DIFS.mother_pos.Y()
+            assert daughters[0].pos.Z() == daughters[1].pos.Z() == DIFS.mother_pos.Z()
+
+        except AssertionError:
+            print("Error on run " + str(i))
+
+            print("mother particle:")
+            print(" E = "     + str(mother_mom.E()))
+            print(" M = "     + str(mother_mom.M()))
+            print(" P = "     + str(mother_mom.P()))
+            print(" Px = "    + str(mother_mom.Px()))
+            print(" Py = "    + str(mother_mom.Py()))
+            print(" Pz = "    + str(mother_mom.Pz()))
+            print(" theta = " + str(mother_mom.Theta()))
+            print(" phi = "   + str(mother_mom.Phi()))
+            print(" x = "     + str(DIFS.mother_pos.X()))
+            print(" y = "     + str(DIFS.mother_pos.Y()))
+            print(" z = "     + str(DIFS.mother_pos.Z()))
+
+            print("daughter 0 particle:")
+            print(" E = "     + str(daughters[0].mom.E()))
+            print(" M = "     + str(daughters[0].mom.M()))
+            print(" P = "     + str(daughters[0].mom.P()))
+            print(" Px = "    + str(daughters[0].mom.Px()))
+            print(" Py = "    + str(daughters[0].mom.Py()))
+            print(" Pz = "    + str(daughters[0].mom.Pz()))
+            print(" theta = " + str(daughters[0].mom.Theta()))
+            print(" phi = "   + str(daughters[0].mom.Phi()))
+            print(" x = "     + str(daughters[0].pos.X()))
+            print(" y = "     + str(daughters[0].pos.Y()))
+            print(" z = "     + str(daughters[0].pos.Z()))
+
+            print("daughter 1 particle:")
+            print(" E = "     + str(daughters[1].mom.E()))
+            print(" M = "     + str(daughters[1].mom.M()))
+            print(" P = "     + str(daughters[1].mom.P()))
+            print(" Px = "    + str(daughters[1].mom.Px()))
+            print(" Py = "    + str(daughters[1].mom.Py()))
+            print(" Pz = "    + str(daughters[1].mom.Pz()))
+            print(" theta = " + str(daughters[1].mom.Theta()))
+            print(" phi = "   + str(daughters[1].mom.Phi()))
+            print(" x = "     + str(daughters[1].pos.X()))
+            print(" y = "     + str(daughters[1].pos.Y()))
+            print(" z = "     + str(daughters[1].pos.Z()))
+
+            raise
+    
+    # Test default arguments
+    epsilon = 2 # increase round off error because the numbers are much larger
+
+    n = 100
+    for i in range(n):
+        DIFS = DIFSampler() 
+        daughters = DIFS.shoot()
+
+        mother_mom = DIFS.mother_mom
+        s = daughters[0].mom+daughters[1].mom
+
+        try:
+            assert DIFS.mother_sampler.pid() == None
+            assert mother_mom.E()**2 -  mother_mom.P()**2 - epsilon <= s.E()**2 - s.P()**2 <= mother_mom.E()**2 - mother_mom.P()**2 + epsilon
+            assert mother_mom.Px() - epsilon <= s.Px() <= mother_mom.Px() + epsilon
+            assert mother_mom.Py() - epsilon <= s.Py() <= mother_mom.Py() + epsilon
+            assert mother_mom.Pz() - epsilon <= s.Pz() <= mother_mom.Pz() + epsilon
+            assert daughters[0].pos.X() == daughters[1].pos.X() == DIFS.mother_pos.X()
+            assert daughters[0].pos.Y() == daughters[1].pos.Y() == DIFS.mother_pos.Y()
+            assert daughters[0].pos.Z() == daughters[1].pos.Z() == DIFS.mother_pos.Z()
+
+        except AssertionError:
+            print("Error on run " + str(i))
+
+            print("mother particle:")
+            print(" E = "     + str(mother_mom.E()))
+            print(" M = "     + str(mother_mom.M()))
+            print(" P = "     + str(mother_mom.P()))
+            print(" Px = "    + str(mother_mom.Px()))
+            print(" Py = "    + str(mother_mom.Py()))
+            print(" Pz = "    + str(mother_mom.Pz()))
+            print(" theta = " + str(mother_mom.Theta()))
+            print(" phi = "   + str(mother_mom.Phi()))
+            print(" x = "     + str(DIFS.mother_pos.X()))
+            print(" y = "     + str(DIFS.mother_pos.Y()))
+            print(" z = "     + str(DIFS.mother_pos.Z()))
+
+            print("daughter 0 particle:")
+            print(" E = "     + str(daughters[0].mom.E()))
+            print(" M = "     + str(daughters[0].mom.M()))
+            print(" P = "     + str(daughters[0].mom.P()))
+            print(" Px = "    + str(daughters[0].mom.Px()))
+            print(" Py = "    + str(daughters[0].mom.Py()))
+            print(" Pz = "    + str(daughters[0].mom.Pz()))
+            print(" theta = " + str(daughters[0].mom.Theta()))
+            print(" phi = "   + str(daughters[0].mom.Phi()))
+            print(" x = "     + str(daughters[0].pos.X()))
+            print(" y = "     + str(daughters[0].pos.Y()))
+            print(" z = "     + str(daughters[0].pos.Z()))
+
+            print("daughter 1 particle:")
+            print(" E = "     + str(daughters[1].mom.E()))
+            print(" M = "     + str(daughters[1].mom.M()))
+            print(" P = "     + str(daughters[1].mom.P()))
+            print(" Px = "    + str(daughters[1].mom.Px()))
+            print(" Py = "    + str(daughters[1].mom.Py()))
+            print(" Pz = "    + str(daughters[1].mom.Pz()))
+            print(" theta = " + str(daughters[1].mom.Theta()))
+            print(" phi = "   + str(daughters[1].mom.Phi()))
+            print(" x = "     + str(daughters[1].pos.X()))
+            print(" y = "     + str(daughters[1].pos.Y()))
+            print(" z = "     + str(daughters[1].pos.Z()))
+
+            raise
+
+   # pass invalid type to mother_sampler 
+    try:
+        DIFS = DIFSampler() 
+        DIFS.mother_sampler = PG.SampledParticle()
+        raise AssertionError("mother_sampler set to improper type")
+    except AttributeError:
+        pass
+
+    # pass derived type to mother_sampler
+    class SP(PG.ParticleSampler):
+        pass
+
+    DIFS = DIFSampler() 
+    DIFS.mother_sampler = SP()
+
+    print("DIFSampler: All unit tests passed")
\ No newline at end of file

Generators/DIFGenerator/python/__init__.py

+# Copyright (C) 2021 CERN for the benefit of the FASER collaboration
+
+from DIFGenerator.DIFSampler import DIFSampler
\ No newline at end of file

Simulation/G4Faser/G4FaserAlg/test/runG4DecayInFlight.py

+#!/usr/bin/env python
+if __name__ == "__main__":
+    import os
+    import sys
+    import GaudiPython
+    import ParticleGun as PG
+    from DIFGenerator import DIFSampler
+    from AthenaConfiguration.ComponentAccumulator import ComponentAccumulator
+    from AthenaConfiguration.ComponentFactory import CompFactory
+    from AthenaCommon.AppMgr import *
+    from AthenaCommon.Logging import log, logging
+    from AthenaCommon.SystemOfUnits import TeV
+    from AthenaCommon.PhysicalConstants import pi
+    from AthenaCommon.Constants import VERBOSE, INFO
+    from AthenaCommon.Configurable import Configurable
+    from CalypsoConfiguration.AllConfigFlags import ConfigFlags
+    from CalypsoConfiguration.MainServicesConfig import MainServicesCfg
+    from AthenaPoolCnvSvc.PoolReadConfig import PoolReadCfg
+    from McEventSelector.McEventSelectorConfig import McEventSelectorCfg
+    from OutputStreamAthenaPool.OutputStreamConfig import OutputStreamCfg
+    from FaserGeoModel.FaserGeoModelConfig import FaserGeometryCfg
+    from G4FaserAlg.G4FaserAlgConfigNew import G4FaserAlgCfg
+    from G4FaserServices.G4FaserServicesConfigNew import G4GeometryNotifierSvcCfg
+#
+# Set up logging and new style config
+#
+    log.setLevel(VERBOSE)
+    Configurable.configurableRun3Behavior = True
+#
+# Input settings (Generator file)
+#
+#   from AthenaConfiguration.TestDefaults import defaultTestFiles
+#   ConfigFlags.Input.Files = defaultTestFiles.EVNT
+#
+# Alternatively, these must ALL be explicitly set to run without an input file
+# (if missing, it will try to read metadata from a non-existent file and crash)
+#
+    ConfigFlags.Input.Files = [""]
+    ConfigFlags.Input.isMC = True
+    ConfigFlags.Input.RunNumber = 12345
+    ConfigFlags.Input.Collections = [""]
+    ConfigFlags.Input.ProjectName = "mc19"
+    ConfigFlags.Common.isOnline = False
+    ConfigFlags.Beam.Type = "collisions"
+    ConfigFlags.Beam.Energy = 7*TeV                              # Informational, does not affect simulation
+    ConfigFlags.GeoModel.FaserVersion = "FASER-01"               # Always needed
+    ConfigFlags.IOVDb.GlobalTag = "OFLCOND-XXXX-XXX-XX"          # Always needed; only the OFLCOND part matters
+# Workaround for bug/missing flag; unimportant otherwise 
+    ConfigFlags.addFlag("Input.InitialTimeStamp", 0)
+# Workaround to avoid problematic ISF code
+    ConfigFlags.GeoModel.Layout = "Development"
+#
+# Output settings
+#
+    ConfigFlags.Output.HITSFileName = "DecayInFlight.HITS.pool.root"
+    ConfigFlags.GeoModel.GeoExportFile = "faserGeo.db" # Optional dump of geometry for browsing in vp1light
+#
+# Geometry-related settings
+# Do not change!
+#
+    ConfigFlags.Detector.SimulateVeto   = True
+    ConfigFlags.Detector.GeometryVeto   = True
+    ConfigFlags.Detector.SimulateTrigger= True
+    ConfigFlags.Detector.GeometryTrigger= True
+    ConfigFlags.Detector.SimulatePreshower   = True
+    ConfigFlags.Detector.GeometryPreshower   = True
+    ConfigFlags.Detector.SimulateFaserSCT   = True
+    ConfigFlags.Detector.GeometryFaserSCT   = True
+    ConfigFlags.Detector.SimulateUpstreamDipole = True
+    ConfigFlags.Detector.SimulateCentralDipole = True
+    ConfigFlags.Detector.SimulateDownstreamDipole = True
+    ConfigFlags.Detector.GeometryUpstreamDipole = True
+    ConfigFlags.Detector.GeometryCentralDipole = True
+    ConfigFlags.Detector.GeometryDownstreamDipole = True
+    ConfigFlags.GeoModel.Align.Dynamic  = False
+    ConfigFlags.Sim.ReleaseGeoModel     = False
+#
+# All flags should be set before calling lock
+#
+    ConfigFlags.lock()
+#
+# Construct ComponentAccumulator
+#
+    acc = MainServicesCfg(ConfigFlags)
+#
+# Particle Gun generator (comment out to read generator file)
+# Raw energies (without units given) are interpreted as MeV
+#
+    pg = PG.ParticleGun()
+    pg.McEventKey = "GEN_EVENT"
+    pg.randomSeed = 123456
+
+    pg.sampler = DIFSampler()
+    acc.addEventAlgo(pg, "AthBeginSeq") # to run *before* G4
+#
+# Only one of these two should be used in a given job
+# (MCEventSelectorCfg for generating events with no input file,
+#  PoolReadCfg when reading generator data from an input file)
+#    
+    acc.merge(McEventSelectorCfg(ConfigFlags))
+    # acc.merge(PoolReadCfg(ConfigFlags))
+#
+#  Output stream configuration
+#
+    acc.merge(OutputStreamCfg(ConfigFlags, 
+                              "HITS", 
+                             ["EventInfo#*",
+                              "McEventCollection#TruthEvent",
+                              "McEventCollection#GEN_EVENT",
+                              "ScintHitCollection#*",
+                              "FaserSiHitCollection#*"
+                            ], disableEventTag=True))
+    acc.getEventAlgo("OutputStreamHITS").AcceptAlgs = ["G4FaserAlg"]               # optional
+    acc.getEventAlgo("OutputStreamHITS").WritingTool.ProcessingTag = "StreamHITS"  # required
+#
+#  Here is the configuration of the Geant4 pieces
+#    
+    acc.merge(FaserGeometryCfg(ConfigFlags))
+    acc.merge(G4FaserAlgCfg(ConfigFlags))
+    acc.addService(G4GeometryNotifierSvcCfg(ConfigFlags, ActivateLVNotifier=True))
+#
+# Verbosity
+#
+#    ConfigFlags.dump()
+#    logging.getLogger('forcomps').setLevel(VERBOSE)
+#    acc.foreach_component("*").OutputLevel = VERBOSE
+#    acc.foreach_component("*ClassID*").OutputLevel = INFO
+#    acc.getService("StoreGateSvc").Dump=True
+#    acc.getService("ConditionStore").Dump=True
+#    acc.printConfig()
+    f=open('FaserG4AppCfg_EVNT.pkl','wb')
+    acc.store(f)
+    f.close()
+#
+# Execute and finish
+#
+    sys.exit(int(acc.run(maxEvents=500).isFailure()))