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Question Energy conservation with QGSP_BERT and one specific pair of seeds 

Forum: Hadronic Processes
Date: 08 May, 2012
From: Leif Raedel <Leif Raedel>

Hello everyone,

I something really odd, which I do not understand at all. I boiled everything down to a basic setup which I want to explain in the following.

Geant4 version: 4.9.4.p03

Setup: My detector volume is a cylinder filled with ice. It is 40m long and has a radius of 30m.

Initial particle: pi+ with 10GeV. It is injected along the symmetry axis of the cylinder.

Output:
In my SteppingAction I sum up all the energy deposition by adding,
    aStep->GetTotalEnergyDeposit();
for all steps.

HepRandom:
I use the following engine:
    CLHEP::RanecuEngine
In EventAction::BeginOfEventAction I set the seeds to,    
    seeds[0] = 1336144155;
    seeds[1] = 38643860;
The problem only occurs for this specific seed.

If I now look at the total energy deposition it is roughly 17GeV. So it is 7GeV LARGER than the primary energy! How is this possible? For every other seed I used the total energy deposition is less than 10GeV, around 8GeV.

The only test I could think of was to have a look at processes that produces a large number of secondaries. Below you can see some of the output. The first interaction looks fine. But the second one is strange. The pi- has a kinetic energy of 0.077GeV at the presteppoint but produces secondaries with a total energy of a least 7GeV. What came to my attention is the fact that the secondary particles that are produced are exactly the same in both interactions, except for the two marked with ***.

If I change any parameter of my simulation the total energy deposition is less than the primary energy as it should be. I stripped my simulation down as far as I could, but still the same result.

Are there any ideas what might cause something like this? Or how I could easily check where it is going wrong?

Cheers, Leif

Name of interacting particle:	pi+
kinetic energy at presteppoint:	9.48439 GeV
kinetic energy at poststeppoint:	0 GeV
step ID:	249
track ID:	1
parent ID:	0
  :----- List of 2ndaries -  15 (Rest= 0,Along= 0,Post=15)
    : 0.00578839 -0.00533029 -17.3629 m     3.18163 GeV                pi0 generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     2.10236 GeV            neutron generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     1.25265 GeV                pi+ generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     854.116 MeV                pi+ generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m      369.54 MeV                pi0 generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     251.089 MeV                pi0 generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     187.293 MeV                pi- generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     160.471 MeV                pi0 generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     111.015 MeV            neutron generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     88.1528 MeV            neutron generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m      23.628 MeV             proton generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     21.3006 MeV             proton generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m      3.9455 MeV              gamma generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     1.33132 MeV              gamma generated by PionPlusInelastic
    : 0.00578839 -0.00533029 -17.3629 m     187.809 keV           C11[0.0] generated by PionPlusInelastic
-------------------------------------------------------------------------------------------------------------
Name of interacting particle:	pi-
kinetic energy at presteppoint:	0.0773503 GeV
kinetic energy at poststeppoint:	0 GeV
step ID:	70
track ID:	256
parent ID:	1
  :----- List of 2ndaries -  17 (Rest= 0,Along= 0,Post=17)
    : -0.309506 0.366112 -17.5161 m     3.18163 GeV                pi0 generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     2.10236 GeV            neutron generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     1.25265 GeV                pi+ generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     854.116 MeV                pi+ generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m      369.54 MeV                pi0 generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     251.089 MeV                pi0 generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     187.293 MeV                pi- generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     160.471 MeV                pi0 generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     111.015 MeV            neutron generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     88.1528 MeV            neutron generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m      23.628 MeV             proton generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     21.3006 MeV             proton generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m      3.9455 MeV              gamma generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     1.33132 MeV              gamma generated by PionMinusInelastic
    : -0.309506 0.366112 -17.5161 m     19.7198 MeV            neutron generated by PionMinusInelastic ***
    : -0.309506 0.366112 -17.5161 m      5.2814 MeV                pi0 generated by PionMinusInelastic ***
    : -0.309506 0.366112 -17.5161 m     187.809 keV           C11[0.0] generated by PionMinusInelastic

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1 Idea: Re: Energy conservation with QGSP_BERT and one specific pair of seeds   (Vladimir Ivanchenko - 23 May, 2012)
2 None: Re: Energy conservation with QGSP_BERT and one specific pair of seeds   (Dennis H. Wright - 16 Jul, 2012)
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