"Smashing more than two": Deuteron production in relativistic heavy ion collisions via stochastic multi-particle reactions

TL;DR

This study introduces a stochastic multi-particle reaction approach in hadronic transport models to improve the simulation of deuteron production in heavy ion collisions, showing faster equilibration and consistent yields.

Contribution

The paper presents the first implementation of stochastic multi-particle reactions in SMASH, replacing artificial resonances to more accurately model deuteron production.

Findings

Multi-particle collisions accelerate deuteron equilibration.

Final deuteron yields are independent of initial conditions.

Transverse momentum and elliptic flow are insensitive to reaction modeling.

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.