Abstract
We present the measurement of the energy dependence of the boron flux in cosmic rays and its ratio to the carbon flux in an energy interval from to based on the data collected by the Calorimetric Electron Telescope (CALET) during of operation on the International Space Station. An update of the energy spectrum of carbon is also presented with an increase in statistics over our previous measurement. The observed boron flux shows a spectral hardening at the same transition energy of the C spectrum, though B and C fluxes have different energy dependences. The spectral index of the B spectrum is found to be in the interval . The B spectrum hardens by , while the best fit value for the spectral variation of C is . The flux ratio is compatible with a hardening of , though a single power-law energy dependence cannot be ruled out given the current statistical uncertainties. A break in the ratio energy dependence would support the recent AMS-02 observations that secondary cosmic rays exhibit a stronger hardening than primary ones. We also perform a fit to the ratio with a leaky-box model of the cosmic-ray propagation in the Galaxy in order to probe a possible residual value of the mean escape path length at high energy. We find that our data are compatible with a nonzero value of , which can be interpreted as the column density of matter that cosmic rays cross within the acceleration region.
- Received 7 October 2022
- Revised 7 November 2022
- Accepted 22 November 2022
DOI:https://doi.org/10.1103/PhysRevLett.129.251103
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society