Measurement of the boron spectrum and the boron-to-carbon and boron-to-oxygen flux ratios with 9 years of on-orbit data of the DAMPE space mission.

The precise measurement of secondary cosmic ray (CR) fluxes provides crucial insights into the propagation and interaction of high-energy particles in the Galaxy. Primary CRs—such as carbon and oxygen nuclei—are believed to interact with the interstellar medium (ISM) and fragment into lighter secondary CRs. Boron is one of the most abundant elements among secondary CRs and its spectrum serves as a valuable probe for CR propagation and interaction. Among all current space-born CR observatories, the DArk Matter Particle Explorer (DAMPE)—in activity since December 2015—is the one with the deepest calorimeter, enabling the direct measurement of CR spectra up to hundreds of TeV. We present the direct measurement of the CR boron spectrum, as well as the boron-to-carbon and boron-to-oxygen flux ratios, from 10~GeV/n up to $\sim$8~TeV/n, using up to 9 years of on-orbit data collected by the DAMPE mission, thus significantly extending the energy range with respect to previous experiments.