Abstract
We study the deuteron production via the deuteron pion and nucleon catalysis reactions, $\pi p n \leftrightarrow \pi d$ and $N p n \leftrightarrow N d$, by employing stochastic multi-particle reactions in the hadronic transport approach SMASH for the first time. This is an improvement compared to previous studies, which introduced an artificial fake resonance $d'$ to simulate these $3 \leftrightarrow 2$ reactions as a chain of $2\leftrightarrow 2$ reactions. The derivation of the stochastic criterion for multi-particle reactions is presented in a comprehensive fashion and its implementation is tested against an analytic expression for the scattering rate and the equilibrating particle yields in box calculations. We then study Au + Au collisions at $\sqrt{s_{\mathrm{NN}}} = 7.7$ GeV, where we find that multi-particle collisions substantially reduce the time required for deuterons to reach partial chemical equilibrium with nucleons. Subsequently, the final yield of $d$ is practically independent from the number of $d$ at particlization, confirming the results of previous studies. The mean transverse momentum and the integrated elliptic flow as a function of centrality are rather insensitive to the exact realization of the $2\leftrightarrow 3$ reactions.
Highlights
In transport simulations of heavy ion collisions the most commonly implemented reactions are 2 → 2 elastic and inelastic scattering, 1 → 2 resonance decays and 2 → 1 resonance formations. (In this notation the integers denote the number of particles at the beginning and at the end of the reaction.) These reactions are the most likely ones to occur in the dilute limit, where transport approaches are applicable and are easier to implement
This work presents the first application of multiparticle reactions in the hadronic transport approach SMASH by employing a stochastic collision criterion
This is of major importance since it allows to treat multiparticle reactions while fulfilling detailed balance
Summary
In transport simulations of heavy ion collisions the most commonly implemented reactions are 2 → 2 elastic and inelastic scattering, 1 → 2 (and sometimes 1 → many) resonance decays and 2 → 1 resonance formations. (In this notation the integers denote the number of particles at the beginning and at the end of the reaction.) These reactions are the most likely ones to occur in the dilute limit, where transport approaches are applicable and are easier to implement. For central Pb+Pb collisions at CERN Large Hadron Collider (LHC) and at energies and further lower energies down tteost√edsNfNor=no7n.7ceGnterVal collisions [9,10] In all these cases the catalysis reactions proceed rapidly enough to keep deuterons in relative equilibrium with nucleons. This work introduces the stochastic criterion in order to treat multiparticle reactions and its application to the deuteron catalysis reactions for the recently established transport approach SMASH [14]. It allows to investigate the difference arising from modeling multiparticle reactions as a chain of two-body reactions (e.g., π π π → ρπ → ω) This helper construct with intermediate resonances is employed in SMASH in several places to adhere to geometric criterion and maintain detailed balance.
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