Properties of Cosmic Deuterons Measured by the Alpha Magnetic Spectrometer

Precision measurements of the cosmic ray D flux are presented as function of rigidity from 1.9 to 21 GV, based on 21 million D nuclei. We observed that over the entire rigidity range D exhibit nearly identical time variations with p, 3 He, and 4 He fluxes. Above 4.5 GV, the D/⁴He flux ratio is time independent and its rigidity dependence is well described by a single power law ∝ R∆ with ∆D/�He = −0.108 ± 0.005. This is in contrast with the ³He/⁴He flux ratio for which we find ∆³He/�He = −0.289 ± 0.003. The significance of ∆D/�He > ∆³He/�He exceeds 10 σ. In addition, we found that above ∼ 13 GV the rigidity dependence of D and p fluxes is identical with a D/p flux ratio of 0.027 ± 0.001. These unexpected observations show that contrary to expectations, cosmic deuterons have a sizeable primary-like component.