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Department of Physics pres.

HEP-Astro Seminar | SuperTIGER in Antarctica: The Hunt for Ultra-Heavy Cosmic Rays

Brian Rauch (Washington University in St. Louis)

The Super Trans-Iron Galactic Element Recorder (SuperTIGER) experiment measures the abundances of the merely relativistic and rare ultra-heavy cosmic rays (UHCR) beyond 26Fe produced in neutron-capture processes. Since the galactic cosmic rays do not point back to their sources we must search for other clues of their origins, and some handles on this are their energy spectra and their detailed elemental and isotopic compositions. The predecessor TIGER instrument made preliminary measurements of UHCR abundances resolving individual elements from 30Zn to 40Zr with two Antarctic flights (2001-2002, 2003-2004) totaling ~50 days. These data support a model of galactic cosmic-ray origins with a dominant contribution from OB association massive star clusters where the source material is enhanced by the outflow and super nova ejecta of these stars (~20%), and in which the more refractory elements that condense into dust grains are preferentially accelerated (~4x) over the volatile ones found as gas. SuperTIGER is over four times the size of TIGER, and with its first 55 day Antarctic flight (2012-2013) confirmed the TIGER findings through 40Zr with good statistics, and with the inclusion of data from a second flight (2019-2020) will extend preliminary UHCR abundance measurements through around 56Ba. Our UHCR observations to date show the galactic cosmic-ray source is enhanced by massive star products over solar system (~5 billion year old ISM), which means this comparatively fresh sample of galactic material can shed light on which heavier elements are significant products of massive stars and their associated supernova (SN) nucleosynthesis. This could help provide constraints on models for the synthesis of heavy elements in binary neutron star mergers (BNSM), for which evidence has been observed in ejected material seen in optical observations following LIGO event GW170817. BNSM are rarer than SN by several orders of magnitude or more, and are unlikely to have contributed to the observed fluxes of the UHCR. I will present on the SuperTIGER science, and the unique challenges and charms of scientific ballooning in Antarctica.

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