Observation of the antimatter helium-4 nucleus
Author(s)Balewski, Jan T.; Betancourt, Michael Joseph; Corliss, Ross Cameron; Hays-Wehle, James Prewitt; Leight, William Axel; Milner, Richard G; Redwine, Robert P; Seele, Joseph Patrick; Steadman, Stephen G; Surrow, Bernd; van Nieuwenhuizen, Gerrit J; Walker, Meredith; STAR Collaboration; ... Show more Show less
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High-energy nuclear collisions create an energy density similar to that of the Universe microseconds after the Big Bang; 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 provides an efficient means of producing and studying antimatter. The antimatter helium-4 nucleus (), also known as the anti-(), consists of two antiprotons and two antineutrons (baryon number B = '4). It has not been observed previously, although the -particle was identified a century ago by Rutherford and is present in cosmic radiation at the ten per cent 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 a factor of about 1,000 with each additional antinucleon. Here we report the observation of, the heaviest observed antinucleus to date. In total, 18 counts were detected at the STAR experiment at the Relativistic Heavy Ion Collider (RHIC; ref. 6) in 10 9 recorded gold-on-gold (Au+Au) collisions at centre-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, providing an indication of the production rate of even heavier antimatter nuclei and a benchmark for possible future observations of in cosmic radiation.
DepartmentMassachusetts Institute of Technology. Laboratory for Nuclear Science; Massachusetts Institute of Technology. Department of Physics; Massachusetts Institute of Technology. Department of Materials Science and Engineering
STAR Collaboration et al. "Observation of the antimatter helium-4 nucleus." Nature 473 (May 2011): 353-356 © 2011 Macmillan Publishers