Search for Cosmic-Ray Antideuterons

We performed a search for cosmic-ray antideuterons using data collected during four BESS balloon flights from 1997 to 2000. No candidate was found. We derived, for the first time, an upper limit of $1.9\times {10}^{-4}$ $({\mathrm{m}}^2\mathrm{s}\mathrm{sr}\mathrm{GeV}/\mathrm{\text{nucleon}}{)}^{-1}$ for the differential flux of cosmic-ray antideuterons, at the 95% confidence level, between 0.17 and $1.15\mathrm{GeV}/\mathrm{\text{nucleon}}$ at the top of the atmosphere.

Figure 1

The surviving single-charge events in the data of each flight. The dotted curves define the $\overline{d}$ mass bands. The dotted vertical lines at $\sim -3.7\mathrm{GV}$ correspond to $E_2$ shown in Fig. 2.

Figure 2

Effective exposure factors of each flight data and their sum. The systematic uncertainty is shown as a $\pm 10\%$ width band. $E_1$ and $E_2$ denote the energy range of the limit.

Figure 3

Obtained upper limit on the $\overline{d}$ flux in comparison with the PBH-$\overline{d}$ spectrum calculated in this Letter. A $\overline{p}$ spectrum measured by BESS and some theoretically predicted spectra of $\overline{p}$ and $\overline{d}$ are shown for reference.