I'm trying to simulate inclusive $\chi_c$ production in $p \bar p$ collisions at very low energies (~ 5.5 GeV) using Pythia8 event generator. Leaving aside problems bounded with applicability of parton model at such low energies, I have encountered the problem that Pythia8 produces baryons ($p \bar p$ mostly, but also neutrons) in the final state in all events (I've tried to simulate more then 100k events).

On the other hand, the total baryon number is zero, and it would seem that also $\pi$ mesons or whatever can be produced instead of baryons (at least in some cases). Since baryons stay in the final state, there is no enough phase volume for significant $p_T$ of $\chi$ meson (at least ~100 MeV) or even it can not be produced because of the nonzero momentum of the remnants. I know that, baryons should stay in final state in some cases at low energies and for that reason some $k$-factor (~0.5) is usually introduced in order to take into account suppression of the inclusive cross section. However, Pythia8 leaves baryons in all events. So, my question is: what are the physical reasons why baryons should always be present in the final state, or may be it is only feature of the Pythia model? In the last case, are there some instruments to suppress baryon production in Pythia?

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    $\begingroup$ BTW--We don't address computational questions as such here: use computational science instead. That said, I think that the question here is "what are the physical reasons why baryons should always be present in the final state [of low energy $p\bar{p}$ interactions]" and that this question therefore belongs here. $\endgroup$ – dmckee Apr 3 '13 at 16:01

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