On nuclear coalescence in small interacting systems

Abstract

The formation of light nuclei can be described as the coalescence of clusters of nucleons into nuclei. In the case of small interacting systems, such as dark matter and $$e^+e^-$$ e + e - annihilations or pp collisions, the coalescence condition is often imposed only in momentum space and hence the size of the interaction region is neglected. On the other hand, in most coalescence models used for heavy ion collisions, the coalescence probability is controlled mainly by the size of the interaction region, while two-nucleon momentum correlations are either neglected or treated as collective flow. Recent experimental data from pp collisions at LHC have been interpreted as evidence for such collective behaviour, even in small interacting systems. We argue that these data are naturally explained in the framework of conventional QCD inspired event generators when both two-nucleon momentum correlations and the size of the hadronic emission volume are taken into account. To include both effects, we employ a per-event coalescence model based on the Wigner function representation of the produced nuclei states. This model reproduces well the source size for baryon emission and the coalescence factor $$B_2$$ B 2 measured recently by the ALICE collaboration in pp collisions.

Formation models for cosmic ray antinuclei

“…This model was later refined and applied to cosmic ray studies and recent LHC data in Refs. [3,4] (see also Ref. [13]).…”

“…This has motivated the suggestion that the production of light nuclei even in small interacting systems can be described using thermal models [1,[19][20][21]. One should thus mention that many of these-including the behaviour of the coalescence factor B 2 as a function of multiplicity [21] and transverse momentum in pp collisions and the decrease in the baryon emission volume with transverse momentum [22]-are naturally described by the WiFunC model [4]. In any case, current evidences for the production of a quark gluon plasma and collective motion in pp collisions are irrelevant for cosmic ray antinuclei studies since they are only observed at LHC energies.…”

“…This proceedings article is mostly based on Refs. [2][3][4]. There, we introduced an improved coalescence model based on the Wigner Function representation of the nucleons and the produced nucleus and applied it to astophysical processes and recent collider data.1 Here, we discuss formation models for cosmic ray antinuclei with a focus on the WiFunC model and its relevance for cosmic ray studies.…”

“…Figure 1: Coalescence momentum p 0 in the per-event coalescence model in momentum space (left) and parameter σ in the WiFunC model (right) obtained by fit to experimental data using different event event generators. The data are taken from Refs [3,4,7]…”

Role of bulk viscosity in deuteron production in ultrarelativistic nuclear collisions

“…where the deuteron wavefunction ϕ d is assumed to be a Gaussian with d = 3.2 fm [43]. The function W is the probability to find a pair of nucleons at positions r d ±r/2 with momenta p d /2 ± q.…”