We encountered a dead-loop in our detector simulation using Geant4.8.1.p01 (hadronic package QGSP). It seems our problem is related to AntiProtonInelastic process. We find that for some low-energy anti-proton, its momentum and direction become to NAN when the program goes to infinite loop. In order to check if the problem is from our side, I did a test using novice/exampleN04 provided by geant4.8.1.p01. First, I did several changes in the eaxmple for antiproton tracking. 1) comment out StackingAction in exampleN04.cc, all scondaries will be reacked: // G4UserStackingAction* stacking_action = new ExN04StackingAction; // runManager->SetUserAction(stacking_action); 2) in ExN04PrimaryGeneratorAction.cc #include "Randomize.hh" G4ParticleDefinition* particle = particleTable->FindParticle (particleName="anti_proton"); set fParticleGun->SetParticleEnergy((51+G4UniformRand()*50)*MeV); 3) use exampleN04.in as macro file: # /mydet/RoIangle 10 deg # /mydet/reqmuon 1 # /mydet/isomuon 1 /control/verbose 1 /run/verbose 1 /tracking/verbose 0 /run/beamOn 1000000 As a result, the same situation was found. The program went to infinite loop at event 44990. See the tracking information below with /tracking/verbose 6 ******************************************************************************** ************************* * G4Track Information: Particle = anti_proton, Track ID = 1, Parent ID = 0 ******************************************************************************** ************************* Step# X Y Z KineE dEStep StepLeng TrakLeng Volume Process 0 0 fm 0 fm 0 fm 67.9 MeV 0 eV 0 fm 0 fm expHall_P initStep >>DefinePhysicalStepLength (List of proposed StepLengths): ++ProposedStep(PostStep ) = 36918.282 : ProcName = AntiProtonInelastic (No ForceCondition) ++ProposedStep(PostStep ) = 208773.54 : ProcName = hElastic (No ForceCondition) ++ProposedStep(PostStep ) = 8.8941426 : ProcName = hIoni (No ForceCondition) ++ProposedStep(PostStep ) = 1.7976931e+308 : ProcName = msc (Forced) ++ProposedStep(PostStep ) = 1.7976931e+308 : ProcName = Transportation (Forced) ++ProposedStep(AlongStep) = 50260.06 : ProcName = hIoni (CandidateForSelection) ++ProposedStep(AlongStep) = 8.894141 : ProcName = msc (NotCandidateForSelection) ++ProposedStep(AlongStep) = 8.894141 : ProcName = Transportation (CandidateForSelection) ... ... ... big skip #Step# X Y Z KineE dEStep StepLeng TrakLeng Volume Process 80 -20.4 cm 34.8 cm -2.44 mm 2.13 MeV 12 MeV 1.26 mm 42.4 cm trackerLayer_phys hIoni >>DefinePhysicalStepLength (List of proposed StepLengths): ++ProposedStep(PostStep ) = 0.05207071664281887 : ProcName = AntiProtonInelastic (No ForceCondition) ++ProposedStep(PostStep ) = 40.82619179226723 : ProcName = hElastic (No ForceCondition) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = hIoni (No ForceCondition) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = msc (Forced) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = Transportation (Forced) ++ProposedStep(AlongStep) = 0.05316910600208757 : ProcName = hIoni (CandidateForSelection) ++ProposedStep(AlongStep) = 0.05186068454676943 : ProcName = msc (NotCandidateForSelection) ++ProposedStep(AlongStep) = 0.05186068454676943 : ProcName = Transportation (CandidateForSelection) >>AlongStepDoIt (process by process): Process Name = Transportation ++G4Step Information Address of G4Track : 0xa346b20 Step Length (mm) : 0.05186068454676943 Energy Deposit (MeV) : 0 ----------------------------------------------------------------------- StepPoint Information PreStep PostStep ----------------------------------------------------------------------- Position - x (mm) : -204.2736407465781 -204.3178574956753 Position - y (mm) : 348.4945252611842 348.5195802058862 Position - z (mm) : -2.436856962280072 -2.42652936189449 Global Time (ns) : 4.329706447170537 4.332279994268195 Local Time (ns) : 4.329706447170537 4.332279994268195 Proper Time (ns) : 4.086523306909923 4.089091033453018 Momentum Direct - x : -0.8524280729078487 -0.8527845550176441 Momentum Direct - y : 0.4834347442858566 0.4828056277504221 Momentum Direct - z : 0.1991412276146746 0.1991412276146747 ... ... ... small skip ... the first nan appears >>PostStepDoIt (process by process): Process Name = AntiProtonInelastic ++G4Step Information Address of G4Track : 0xa346b20 Step Length (mm) : 0.05207071664281887 Energy Deposit (MeV) : 2.05859873404215 ----------------------------------------------------------------------- StepPoint Information PreStep PostStep ----------------------------------------------------------------------- Position - x (mm) : -204.2736407465781 -204.319970104144 Position - y (mm) : 348.4945252611842 348.5154997473365 Position - z (mm) : -2.436856962280072 -2.425683387001505 Global Time (ns) : 4.329706447170537 4.332279994268195 Local Time (ns) : 4.329706447170537 4.332279994268195 Proper Time (ns) : 4.086523306909923 4.089091033453018 Momentum Direct - x : -0.8524280729078487 nan Momentum Direct - y : 0.4834347442858566 nan Momentum Direct - z : 0.1991412276146746 nan Momentum - x (MeV/c): -53.88345198779397 nan Momentum - y (MeV/c): 30.55874584714016 nan Momentum - z (MeV/c): 12.58806123120922 nan Total Energy (MeV) : 940.3991873554132 938.3405886213711 Kinetic Energy (MeV): 2.126887355413274 0.06828862137112379 Velocity (mm/ns) : 20.15144179563204 3.616776901458536 Volume Name : trackerLayer_phys trackerLayer_phys Safety (mm) : 0.7969176405153779 0.8333978912969117 Polarization - x : 0 0 Polarization - y : 0 0 Polarization - Z : 0 0 Weight : 1 1 Step Status : AlongStep Proc. PostStep Proc Process defined Step: hIoni AntiProtonInelastic ----------------------------------------------------------------------- ... ... ... small skip #Step# X Y Z KineE dEStep StepLeng TrakLeng Volume Process 81 -20.4 cm 34.9 cm -2.43 mm 68.3 keV 2.06 MeV 52.1 mum 42.4 cm trackerLayer_phys AntiProtonInelastic >>DefinePhysicalStepLength (List of proposed StepLengths): ++ProposedStep(PostStep ) = 44.52449073783492 : ProcName = AntiProtonInelastic (No ForceCondition) ++ProposedStep(PostStep ) = 36.7761184247093 : ProcName = hElastic (No ForceCondition) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = hIoni (No ForceCondition) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = msc (Forced) ++ProposedStep(PostStep ) = 1.797693134862316e+308 : ProcName = Transportation (Forced) ++ProposedStep(AlongStep) = 0.000767365494101051 : ProcName = hIoni (CandidateForSelection) ++ProposedStep(AlongStep) = 0.0007558743340329251 : ProcName = msc (NotCandidateForSelection) The program stopped here. How to solve this problem? Momentum is nan, why? Thanks in advanced.
This seems the problem is not in the original exampleN04 but related to antiproton process. This problem is thus forwarded to the hadronics working group.
Problem was due to un-initialized kinematics being returned if the anti-proton energy was very low ( < 0.1 MeV). Now the exact kinematics of the anti-proton as it enters the model is returned (essentially performing no hadronic interaction). The fix will be included in the next release. Contact me if you need the fix before then.
