Antiproton production in pp, dp and dd collisions close to threshold

The production of antiprotons in $pp$ collisions is investigated close to threshold where experimental data about the total cross section are not available. We analyze the latter reaction within the LUND string model for inclusive $\bar{p}$ production and within the framework of a one-boson exchange model for the exclusive reaction $pp \rightarrow ppp\bar{p}$. The application of our new results to the analysis of subthreshold antiproton production in $d + p$ and $d + d$ collisions shows cross sections that are much lower than expected before. Nevertheless, the comparison of experimental $\bar{p}$ differential cross sections from $d +p$ and $d + d$ is expected to provide valuable information about a nonnucleonic component in the deuteron wavefunction.