Cosmic ray energy spectrum and composition measurements from the GRAPES-3 experiment: Latest results

The Gamma Ray Astronomy at PeV EnergieS phase-3 (GRAPES-3) experiment is located at Ooty in India (11.4◦ N, 76.7◦ E and 2200 m above m.s.l.). It consists of a densely packed array of 400 plastic scintillator detectors and a large area muon telescope (560 m2). It measures cosmic rays from several TeV to over 10 PeV energies providing a substantial overlap with direct experiments while covering the knee region. Shower parameters are reconstructed by fitting the observed particle densities with the NKG lateral distribution function (LDF). For this analysis, the QGSJET-II-04 hadronic interaction model is used to generate the air shower simulation data for proton, helium, nitrogen, aluminium, and iron primaries. Precise measurements of the average nuclear composition are obtained by fitting muon multiplicity distributions (MMDs) for all simulated primaries with the MMDs measured by the muon telescope. Details of the analysis and preliminary results for the extracted composition and elemental energy spectrum for proton and helium from a few tens of TeV to a few PeV will be presented.