[fluka-discuss]: Re: Fluka process gamma -> mu+ mu-

From: Andrea Celentano <andrea.celentano_at_ge.infn.it>
Date: Mon, 20 Aug 2018 16:33:13 +0200

Dear Fluka community,
I come back to this message, since I think there may be an issue with the process gamma -> mu+ mu- being “recognized” in mgdraw.f, entry USDRAW.

I want to underline that the process itself, as implemented in FLUKA, works correctly, also regarding the corresponding bias. In particular, I did a comparison between a fluka-based and a Geant4-based simulation, with an 11-GeV electron beam impinging on a thick aluminum target, scoring the number of muons exiting from the target, as a function of their energy, and I got an excellent agreement. The process gamma-> mu+ mu- was turned on in G4 by hand.

I am now trying to identify each produced muon, both by the decay of a pion/kaon, by the gamma-> mu+ mu- process, or by other more rare processes. For each produced muon, I write to an output file the energy, the direction, and the production vertex, together with the processID that produced it, and the mother particle ID and energy.

The code mgdraw.f code I am using is the following (entry USDRAW)

 if ((JTRACK.ne.10).and.(JTRACK.ne.11)) then
           do ip=1,np
              if ((KPART(IP).eq.10).or.(KPART(IP).eq.11)) then
            CALL eventcreate(NCASE,1,KPART(IP),TKI(IP),
            CALL eventsave
            end if
           end do
         end if

In particular, I am checking every interaction, looking for secondaries. If any secondary is a muon, I write it to my file trough the “eventcreate - vertexsave - eventsave” routines. The first “IF” is used to exclude processes where the impinging particle is a muon, such as mu N -> mu N X, i.e. inelastic (or elastic) interaction of the muon itself.

In my output file, I see many events, all of them with ICODE=102 (particle decay secondaries), and none with ICODE corresponding to gamma -> mu+ mu- (should be 104, pair production, according to the message by Stefan Rosler).

I tried to remove the first IF statement, and I saw in the output some events with ICODE=104, associated only to mu -> mu e+ e- (radiative pair production by muon), some with ICODE=103, associated to mu->mu e- (delta ray), and with ICODE=105, associated to mu -> mu gamma (muon bremmstrahlung).
However, still I did not saw any event with ICODE=104, where the primary particle is a photon.

In other words, I think that this process, even if properly implemented in Fluka, does not get “exported” to mgdraw.f, entry USDRAW.
Is this possible? (I see that this process is a particular one, to be explicitly activated through the PHOTONUC card, SDUM=MUMUPAIR - maybe the issue is related to this?)


> On Jun 21, 2017, at 12:06, Andrea Celentano <andrea.celentano_at_ge.infn.it> wrote:
> Dear fluka community,
> I have a question regarding the process gamma -> mu+ mu-.
> In my simulation, I explicitly activated it trough the card:
> (I am using a strong bias for it)
> When such a process happens, which of the flags reported in (EVTFLG) is switched on?
> The question arises from the fact that I'd like to modify the stuprf.f function in order to save, for muons, the mother particle and the process id that produced it.
> I already verified that my code works properly when the muon is produced by the decay of another particle (usually pions), or due to the inelastic interaction of another muon with a nucleus. However, I can't find the flag for the aforementioned process.
> For completeness, I attach to this email the stuprf.f code I am using
> Bests
> Andrea Celentano
> <stuprf.f>

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Received on Mon Aug 20 2018 - 17:45:51 CEST

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