The search for antihelium in cosmic rays using data from the PAMELA experiment

The generally accepted theory explaining the observed cosmological baryon asymmetry involves mechanisms of baryosynthesis that generate asymmetry in an initially baryon symmetric Universe. Due to the possible inhomogeneous spatial nature of such mechanisms, antimatter domains could arise in the Universe. This hypothesis can be tested by the direct measurement of fluxes of antinuclei in cosmic rays. Searching for antihelium nuclei is therefore among the objectives of the PAMELA experiment. We analyzed data from August 2006 to December 2009 and obtained a preliminary value for the upper limit of the antihelium/helium flux ratio that could lead to some restrictions on the existing theoretical models of the production and propagation of antimatter in the Galaxy.