Simulation

The simulation program is part of the DD4Hep package, which uses as main components the ROOT geometry package, which is used for construction and visualization of geometry, and the Geant4 simulation toolkit, which can be interfaced via DD4hep to perform detector simulation in complex detector designs.

In the MuC-Tutorial/simulation/ directory you can find the examples configuration file to be used by the simulation command: ddsim

To go to the directory use the command line:

cd ~/MuC-Tutorial/simulation/

All the options can be passed as arguments to the command line, but probably the easiest way is to set everything in the steering file and then invoke for example:

ddsim --steeringFile steer_sim_Hbb.py > sim.log 2>&1

Looking in the configuration file you can see for example:

SIM.compactFile = "/opt/ilcsoft/muonc/detector-simulation/geometries/MuColl_v1/MuColl_v1.xml"  # ← path to the geometry definition
SIM.inputFiles = ["/data/samples/HH/mumu2H2bb750.stdhep"] # ← Input file
SIM.outputFile = "mumu_H_bb.slcio" # ← Output file
SIM.numberOfEvents = 10 # ← Number of events to be simulated

Use the output of the command ddsim -h to see all the other parameters that you can set.

Simulating single particles:

It is sometimes useful for performance studies to simulate events with single particles (muons, pions, electrons etc) with specific parameters. To learn how to do this, you can look at the configuration file MuC-Tutorial/simulation/advanced/steer_sim_muGun.py. In this file you can specifically set the following parameters:

SIM.enableGun = True

You can also set parameters of the particle i.e. type, energy, distribution in theta and phi. You can also decide if you want just one particle per event or more. For example:

SIM.gun.particle = "mu-" # muon
SIM.gun.energy = 10.0*GeV  #fixed energy at 10 GeV
SIM.gun.distribution = "uniform"  # flat in theta distribution    

SIM.gun.isotrop = True. #isotropic distribution in Phi
SIM.gun.multiplicity = 1 # one muon per event
SIM.gun.phiMax = None
SIM.gun.phiMin = None
SIM.gun.thetaMax = 172*deg
SIM.gun.thetaMin = 8*deg

You can also define parameters of the beamspot for your particle gun sample, where you provide vertex sigma in cm. To get the correct beamspot position for the COM energy you are trying to simulate, you can refer to this accelerator table: https://muoncollider.web.cern.ch/design/general-parameters

SIM.vertexSigma = [0.0, 0.0, 0.0, 0.0]

You can then execute it as usual:

ddsim --steeringFile steer_sim_muGun.py > sim.out 2>&1