Probing cosmic ray composition with inclined air showers of LHAASO-KM2A
July 25, 2023
The origin of cosmic ray (CR) spectral knee around ∼4 PeV is unknown. Composition studies
around the knee can provide information on the CR sources and propagation. LHAASO-KM2A
is capable of simultaneously measuring the EM and muonic components in extensive air showers.
The triggered events of LHAASO-KM2A are dominated by CRs of higher energies at larger zenith
angles because of the increasing atmospheric attenuation. In this work, we use the KM2A observed
spectrum of muon-to-electron number ratio to constrain CR composition around the knee. The
muon-to-electron number ratio spectra are compared between Monte Carlo (MC) simulation and
experiment data over a wide zenith angle range. We report a MC excess at large zenith angles,
which sets an upper limit on CR Fe flux at PeVs. Systematic uncertainties of interaction models
and atmospheric models are briefly discussed.
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