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Properties of Cosmic Helium Isotopes Measured by the Alpha Magnetic Spectrometer

  • AMS Collaboration
  • CIEMAT
  • I. Physics Institute and JARA-FAME
  • RWTH Aachen University
  • National Institute for Nuclear Physics
  • Laboratório de Instrumentação e Física Experimental de Partículas
  • Jülich Supercomputing Centre and JARA-FAME
  • Jülich Research Centre
  • Université Grenoble Alpes
  • CERN
  • University of Groningen
  • INFN TIFPA
  • University of Trento
  • Massachusetts Institute of Technology
  • University of Perugia
  • Physics and Astronomy Department
  • University of Hawai'i at Mānoa
  • Institut für Experimentelle Teilchenphysik
  • Karlsruhe Institute of Technology
  • NASA Johnson Space Center
  • University of Rome La Sapienza
  • University of Geneva
  • National Research Council of Italy
  • Physics Department and Center for High Energy and High Field
  • National Central University
  • CAS - Institute of High Energy Physics
  • University of Chinese Academy of Sciences
  • Shandong University
  • University of Bologna
  • CAS - Institute of Electrical Engineering

Research output: Contribution to journal › Article › peer-review

Abstract

Precision measurements by the Alpha Magnetic Spectrometer (AMS) on the International Space Station of He3 and He4 fluxes are presented. The measurements are based on 100 million He4 nuclei in the rigidity range from 2.1 to 21 GV and 18 million He3 from 1.9 to 15 GV collected from May 2011 to November 2017. We observed that the He3 and He4 fluxes exhibit nearly identical variations with time. The relative magnitude of the variations decreases with increasing rigidity. The rigidity dependence of the He3/He4 flux ratio is measured for the first time. Below 4 GV, the He3/He4 flux ratio was found to have a significant long-term time dependence. Above 4 GV, the He3/He4 flux ratio was found to be time independent, and its rigidity dependence is well described by a single power law ∈RΔ with Δ=-0.294±0.004. Unexpectedly, this value is in agreement with the B/O and B/C spectral indices at high energies.

Original languageEnglish
Article number181102
JournalPhysical Review Letters
Volume123
Issue number18
DOIs
StatePublished - 1 Nov 2019

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