2011/03/22 by H. Agakishiev, STAR Collaboration, A. V. Alakhverdyants +98 · 3 citations
Physics and Astronomy · #High-Energy Particle Collisions Research #Nuclear physics research studies #Particle physics theoretical and experimental studies #nucl-ex
paper · pdf · doi:10.1038/nature10079
published as Nature 473, 353-356 (19 May 2011) · 19 pages, 4 figures. Submitted to Nature. Under media embargo
arxiv created 2011/03/22 · openalex publication_date 2011/04/21 · crossref created 2011/04/21 · crossref issued 2011/04/24 · crossref published 2011/04/24 · crossref published-online 2011/04/24 · crossref published-print 2011/05/19 · arxiv updated 2015/03/18 · openalex created_date 2016/06/24 · crossref deposited 2023/05/18 · crossref indexed 2026/07/07 · openalex updated_date 2026/08/01
High-energy nuclear collisions create an energy density similar to that of the universe microseconds after the Big Bang, and in both cases, matter and antimatter are formed with comparable abundance. However, the relatively short-lived expansion in nuclear collisions allows antimatter to decouple quickly from matter, and avoid annihilation. Thus, a high energy accelerator of heavy nuclei is an efficient means of producing and studying antimatter. The antimatter helium-4 nucleus (4He), also known as the anti-α (α), consists of two antiprotons and two antineutrons (baryon number B=-4). It has not been observed previously, although the α particle was identified a century ago by Rutherford and is present in cosmic radiation at the 10% level. Antimatter nuclei with B < -1 have been observed only as rare products of interactions at particle accelerators, where the rate of antinucleus production in high-energy collisions decreases by about 1000 with each additional antinucleon. We present the observation of the antimatter helium-4 nucleus, the heaviest observed antinucleus. In total 18 4He counts were detected at the STAR experiment at RHIC in 109 recorded Au+Au collisions at center-of-mass energies of 200 GeV and 62 GeV per nucleon-nucleon pair. The yield is consistent with expectations from thermodynamic and coalescent nucleosynthesis models, which has implications beyond nuclear physics.