Antiprotons in the cosmic radiation

Cosmic ray antiprotons were first detected three years ago by Golden et al. (1979) and Bogomolov et al. (1979). The measured flux at about 10 GeV was found to be a factor of 5 to 10 higher than expected in the leaky box model. More recently, an unexpected high antiproton flux has been measured by Buffington et al. (1981) at about 200 MeV, well below a low energy cut-off in the spectrum expected if the antiprotons are secondary. This paper briefly reviews calculations of the flux of secondary antiprotons expected for different models of cosmic ray propagation and discusses some of the primary origin hypotheses which have been proposed to account for the data.