SuperTIGER Measurements Through ₅₆Ba and Their Implications

SuperTIGER (Super Trans-Iron Galactic Element Recorder) is a long-duration-balloon-borne cosmic-ray detector that had a 55-day record breaking Antarctic flight during the 2012-2013 austral summer and a 32-day one in 2019-2020. The first flight measured the relative abundances of Galactic cosmic-ray (GCR) nuclei with high statistical precision and well resolved individual element peaks from ₁₀Ne to ₄₀Zr, and preliminary lower-statistics measurements out to ₅₆Ba. The measurements through ₄₀Zr support an OB association model source where refractory elements are preferentially injected into the supernovae-shock accelerator over volatile ones superposed on a sputtering cross-section Z dependence. However, the preliminary GCR measurements above ₄₀Zr are inconsistent with this model, requiring a modification to the injection mechanism and/or another GCR source component. Recent multi-messenger observations have established kilonovae as one of the sites of r-process nucleosynthesis, suggesting that a mixture of NS-NS mergers, other core-collapse events and supernovae may contribute significantly to the heavy r-process budget of the universe. We report the status of SuperTIGER and progress in refining the interesting GCR results above ₄₀Zr and note that future heavy cosmic-ray abundance measurements in the Milky Way may be able to further constrain sites of r-process nucleosynthesis.