  The study of antinuclei in cosmic rays provides a unique opportunity to probe
physics beyond the Standard Model. Antinuclei in our Galaxy may stem either
from annihilation or decay of dark matter, or from collisions of cosmic rays
with the interstellar medium, which constitute the background of indirect dark
matter searches. Understanding the formation mechanism of (anti)nuclei is
crucial for setting limits on their production in space. Coalescence models,
which describe the formation of light nuclei from final-state interaction of
nucleons, have been widely employed in high-energy collisions. In this work, we
introduce ToMCCA (Toy Monte Carlo Coalescence Afterburner), which allows for
detailed studies of the nuclear formation processes without the overload of
general-purpose event generators. ToMCCA contains parameterizations of the
multiplicity dependence of the transverse momentum distributions of protons and
of the baryon-emitting source size, extracted from ALICE measurements in pp
collisions at $\sqrt{s} = 5 - 13$ TeV, as well as of the event multiplicity
distributions, taken from the EPOS event generator. ToMCCA provides predictions
of the deuteron transverse momentum distributions, with an agreement of
$\sim5\%$ with the experimental data. The results of ToMCCA show that the
coalescence mechanism in pp collisions depends only on the event multiplicity
rather than on the collision system or its energy. This allows the model to be
utilized for predictions at lower center-of-mass collision energies, which are
the most relevant for the production of antinuclei from processes related to
dark matter. This model can also be extended to heavier nuclei as long as the
target nucleus wave function and its Wigner function are known.
