Physics HEPAP/CPGA Seminar
Physics HEPAP/CPGA Seminar
Galactic cosmic rays (GCR) are measured directly with detectors flown above all or most of the atmosphere, such as the CALorimetric Electron Telescope (CALET) and the Super Trans-Iron Galactic Element Recorder (SuperTIGER). SuperTIGER has flown successfully twice on stratospheric balloons over Antarctica in the 2012-2013 and 2019-2020 seasons at altitudes up to ~130,000 ft and above all but the last ~0.5% of the atmosphere. CALET has been flying on the International Space Station (ISS) in low earth orbit since its launch on HTV-5 rocked in and installation on the ISS in August 2015. Both of these instruments are contributing to our understanding of the origin and transport of the galactic cosmic rays by measuring their energy spectra and their detailed elemental compositions.
SuperTIGER uses a combination of large area scintillator detectors, Cherenkov counters and scintillating-fiber hodoscopes to measure the abundances of the merely relativistic and rare ultra-heavy cosmic rays (UHCR) beyond 26Fe produced in neutron-capture processes. Measurements from the two flights of the predecessor TIGER instrument and the first SuperTIGER flight have supported 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. The combined data from the two SuperTIGER flights will extend preliminary UHCR measurements to 56Ba, which could begin shed light on which of these 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, which are rarer than SN by several orders of magnitude or more and are unlikely to have contributed to the observed fluxes of the UHCR.
CALET is a high-energy astroparticle physics experiment developed and operated by Japan in collaboration with researchers in Italy and the US, which began science operations in mid-October 2015 and is now approved to continue through March 2021. In extended observations the main calorimeter (CAL) can measure the cosmic-ray combined electron and positron spectrum up to 20 TeV, gamma rays up to 10 TeV, and nuclei from 1H to 40Zn up to 1,000 TeV. The CAL is comprised of a two-layer scintillator paddle charge detector, a scintillating fiber imaging calorimeter with 3 radiation lengths (r.l.) of tungsten plates, and a 27 r.l. deep lead tungstate total absorption calorimeter. There is also the CALET Gamma-ray Burst Monitor (CGBM) subsystem with two hard X-ray monitors (HXM) sensitive to 7-1000 keV photons and a soft gamma-ray monitor (SGM) sensitive to 100 keV-20 MeV photons utilizing two LaBr3 (Ce) and one BGO scintillators, respectively. Major CALET results to date include measurements of the combined electron and positron energy spectrum to ~5 TeV, the spectra of protons and other nuclei, and gamma-ray observations including LIGO/Virgo counterpart searches.