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Forum: Hadronic Processes
Re: Question PiMinusAbsorptionBertini multiple calls (Sam)
Re: None Re: PiMinusAbsorptionBertini multiple calls (Michael H. Kelsey)
Re: None Re: PiMinusAbsorptionBertini multiple calls (Sam)
Date: 11 Jun, 2012
From: Michael H. Kelsey <Michael H. Kelsey>

On Mon, 11 Jun 2012 07:37:49 GMT, Sam wrote:
> I am using 9.5.p01. Here is the output for /tracking/verbose 2.
> 
> ---> Begin of Event: 0
> 
> *********************************************************************************************************
> * G4Track Information:   Particle = pi-,   Track ID = 1,   Parent ID = 0
> *********************************************************************************************************
> 
> Step#      X         Y         Z        KineE    dEStep   StepLeng  TrakLeng    Volume     Process
>     0    873 um  -4.11 mm   -1.3 cm      1 MeV     0 eV      0 fm      0 fm     D2target    initStep
>     1    996 um  -4.22 mm  -1.32 cm    668 keV   332 keV   240 um    240 um     D2target       hIoni
>     2   1.08 mm  -4.29 mm  -1.33 cm    281 keV   387 keV   172 um    412 um     D2target       hIoni
>     3   1.11 mm  -4.31 mm  -1.33 cm      0 eV    281 keV  51.8 um    463 um     D2target       hIoni
>     4   1.11 mm  -4.31 mm  -1.33 cm      0 eV      0 eV      0 fm    463 um     D2target  PiMinusAbsorptionBertini
>     :----- List of 2ndaries - #SpawnInStep=  3(Rest= 3,Along= 0,Post= 0), #SpawnTotal=  3 ---------------
>     :   1.11 mm  -4.31 mm  -1.33 cm   29.8 MeVanti_nu_mu
>     :   1.11 mm  -4.31 mm  -1.33 cm   4.12 MeV       mu-
>     :   1.11 mm  -4.31 mm  -1.33 cm      1 keV       pi-
>     :----------------------------------------------------------------- EndOf2ndaries Info ---------------

Ah, ha! This gives me the clue I needed, and makes me think the problem isn't with PiMinusAbsorptionBertini itself. In fact, as I'll discuss below, I don't understand how the process gets onto the step listing at all. The bottom line is that it looks, from the above, like there is a bug in the process which decays pi-. The final state ought to have just the neutrino and muon.

My discussion in my previous post was irrelevant, so please ignore it.

At zero energy, the pi- on most nuclei will be absorbed on a nucleon and convert it to an exciton (here, pi- p -> n exciton). The excess energy will either break up the nucleus or put it into an excited state which relaxes via gamma emission. For that to happen, the nucleus must have a non-zero absorption cross-section in order for the process-manager to choose the process.

Deuterons, along with the other light nuclei (H, T, He-3, He-4) have identically zero absorption cross section for pi-. Hence, the process doesn't actually get invoked, and the pi- at rest is returned to tracking. At that point, the system decays the pion in situ, which should form a mu/nu. The fact that it also puts a pi- back onto the track list is wrong, and needs to be fixed.

As a side note, I don't understand why the absorption process name is what gets printed out, but I've seen similar oddities with the final process name elsewhere (e.g., having Scintillation be the final process for neutrons).

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1 None: Re: PiMinusAbsorptionBertini multiple calls   (Sam - 11 Jun, 2012)
(_ None: Re: PiMinusAbsorptionBertini multiple calls   (Mike Kelsey - 11 Jun, 2012)
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