Precision Measurement of Cosmic-Ray Nitrogen and its Primary and Secondary Components with the Alpha Magnetic Spectrometer on the International Space Station
M. Aguilar, L. Ali Cavasonza, B. Alpat, G. Ambrosi, L. Arruda, N. Attig, S. Aupetit, P. Azzarello, A. Bachlechner, F. Barao, A. Barrau, L. Barrin, A. Bartoloni, L. Basara, S. Başeğmez-du Pree, M. Battarbee, Roberto Battiston
Dec - 2018
DOI: 10.1103/physrevlett.121.051103

journal : Physical Review Letters

Volume : 121 ; Issue : 5
type: Article Journal

A precision measurement of the nitrogen flux with rigidity (momentum per unit charge) from 2.2 GV to 3.3 TV based on 2.2×106 events is presented. The detailed rigidity dependence of the nitrogen flux spectral index is presented for the first time. The spectral index rapidly hardens at high rigidities and becomes identical to the spectral indices of primary He, C, and O cosmic rays above ∼700  GV. We observed that the nitrogen flux ΦN can be presented as the sum of its primary component ΦPN and secondary component ΦSN, ΦN=ΦPN+ΦSN, and we found ΦN is well described by the weighted sum of the oxygen flux ΦO (primary cosmic rays) and the boron flux ΦB (secondary cosmic rays), with ΦPN=(0.090±0.002)×ΦO and ΦSN=(0.62±0.02)×ΦB over the entire rigidity range. This corresponds to a change of the contribution of the secondary cosmic ray component in the nitrogen flux from 70% at a few GV to <30% above 1 TV.

keywords :

Notes : Research funded by Agenzia Spaziale Italiana (2013-002-R.0, 2014-037-R.0)