Alternative coalescence model for deuteron, tritium, helium-3 and their antinuclei

Abstract

Antideuteron and antihelium nuclei have been proposed as a detection channel for dark matter annihilations and decays in the Milky Way, due to the low astrophysical background expected. To estimate both the signal for various dark matter models and the astrophysical background, one employs usually the coalescence model in a Monte Carlo framework. This allows one to treat the production of antinuclei on an event-by-event basis, taking thereby into account momentum correlations between the antinucleons involved in the process. The standard coalescence approach lacks however an underlying microscopic picture, and the numerical value of the coalescence parameter obtained from fits to different reactions varies considerably. Here we propose a coalescence model which is based on the Wigner function representations of the produced antinuclei states. This approach allows us to include in a semi-classical picture both the size of the formation region, which is process dependent, and momentum correlations. The model contains a single, universal parameter which is fixed by fitting the production spectra of antideuterons in proton-proton interactions at the Large Hadron Collider. Using this value, the model describes well the production of various antinuclei both in electron-positron annihilation and in proton-proton collisions.

Formation of light (anti)nuclei

“…the sum of two Gaussians as introduced in Ref. [5]. 4 In order to proceed, one has to provide a prescription for the nucleon Wigner function.…”

“…frame of the particle collision, while σ ⊥/ describes the characteristic spatial spread of nucleons in the perpendicular/parallel direction in the lab frame. 6 The effective Lorentz boost of the transverse spread is included to account for the boost between the lab frame and the deuteron rest frame [5]. In Eq.…”

“…In Ref. [5], we developed a new coalescence model for deuteron, tritium and helium-3 based on the Wigner function representation of the produced nuclei states (the abbreviation WiFunC, short for Wigner Function with Correlations, will be used for this model). The model was later refined and applied in Ref.…”

“…In subsection 3.4 we update and extend the fits to experimental data from Refs. [5,6] based on new insights. The numerical implementation of the WiFunC model is outlined in section 4.…”

Measurement of the Low-Energy Antideuteron Inelastic Cross Section

“…At the LHC, the ALICE Collaboration has studiedp,d, 3H e, and 4H e production in pp, p-Pb, and Pb-Pb collisions at center-of-mass energies per nucleon pair from 0.9 to 13 TeV [26][27][28][29][30][31][32], and the yields obtained for A ≥ 2 have been interpreted by means of coalescence or statistical hadronization models [33][34][35][36]. The LHC measurements combined with different coalescence models have been employed to estimate the antideuteron and antihelium flux from cosmic-ray interactions measurable by the AMS-02 and GAPS experiments [15,[37][38][39]. Since the inelastic cross sections for antinuclei-nuclei interactions are measured precisely only forp but barely known for heavier antinuclei, all the available calculations rely on poorly constrained parametrizations.…”