Speaker
Description
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${}^{\Delta}$ with ∆${}_{D/⁴He}$ = −0.108 ± 0.005. This is in contrast with the ³He/⁴He flux ratio for which we find ∆${}_{³He/⁴He}$ = −0.289 ± 0.003. The significance of ∆${}_{D/⁴He}$ > ∆${}_{³He/⁴He}$ 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.
