## 5 Elemental Composition in the \(10^{14}\) to \(10^{18}\) eV Region
The cross-calibration of fluxes in this energy range, where the boundary line between 'direct' and 'indirect'  
Figure 5: Energy spectra of the light (p+He) component as measured by Tibet AS\(\gamma\)[25; 31] and ARGO-YBJ [52] experiments with different techniques and analyses, compared with results obtained in direct observations by CREAM [57] and NUCLEON [58]. measurements is uncertain, is very important. The low energy threshold allowed also a calibration of the absolute energy scale at a level of 10% exploiting the _Moon Shadow_ technique in the 1-30 TeV/\(Z\) range [20]. As can be seen from the figure, the observations of Tibet AS\(\gamma\) and ARGO-YBJ are in good agreement each other showing that the knee of the (p+He) energy spectrum is at \(\approx\)500-700 TeV, well below the energy of knee in the all-particle spectrum. Similar conclusions have been obtained by the BASJE-MAX experiment located at 5200 m asl [21] and by EAS-TOP at 2000 m asl [53] and by CASA-MIA at 1450 m asl [26]. In Figure 6 the energy spectra of the light component reconstructed by the KASCADE experiment [22; 23; 24] with two different hadronic interaction models are added for comparison. The energy threshold is about 1 PeV and the experiment was located at sea level. KASCADE did use of a complex unfolding procedure to recover the elemental composition from the \(N_{e}-N_{\mu}\) diagram in terms of 5 mass groups (p, He, CNO, MgSi, Fe). As can be seen from the figure, both the spectra are at variance with the results obtained by Tibet AS\(\gamma\) and ARGO-YBJ, suggesting that the knee of the CR all-particle spectrum at a few PeV is due to the bending of the light component. All measurements of the light component up to about 10\({}^{18}\) eV are summarized in the Figure 7 and compared with the parametrization provided by [PERSON] [62]. Roughly speaking, we can separate the experiments that measured the (p+He) energy spectrum in the PeV range in 2 different groups  
1. arrays located at extreme altitude (BASJE-MAS at 5200 m asl, ARGO-YBJ and Tibet AS\(\gamma\) at 4300 m asl) observing a composition at the knee heavier than (p+He). These experiments did not exploit the measurement of the muon component to recover the elemental composition;
2. arrays located deeper in the atmosphere (KASCADE, KASCADE-Grande and Ice-Top/Ieccube) reporting evidence that the light cut-off is located at a few PeV. In this case both low and high energy muons have been used in the classical study of \(N_{e}-N_{\mu}\) correlation. Figure 6: The energy spectra shown in Figure 5 compared with the results obtained by the KASCADE experiment by using two different interaction models to interpret data [22; 23; 24]. Measurements exploiting the longitudinal profile of the showers with Cherenkov detectors are conflicting too. The results obtained with the ARGO-YBJ hybrid detector (carpet and Cherenkov telescope) are in agreement with those of the carpet only, whereas the observations of Cherenkov light by Tunka-133 are consistent with KASCADE and KASCADE-Grande findings. In Figure 8 the all-particle energy spectrum measured by several experiments in the energy region \(10^{16}\)-\(10^{18}\) eV is shown. As can be seen, the spectrum cannot be fitted by a single power law. We observe a spectral hardening at \(\sim\)2 \(\times\)\(10^{16}\) eV and a steepening at \(\sim\)\(10^{17}\) eV. This result was first pointed out by KASCADE-Grande experiment [64, 65], then more firmly assessed with higher statistics and precision by Tunka-133 and IceTop-73 [28, 29], in particular for the feature at \(\sim\)2 \(\times\)\(10^{16}\) eV. The _light_ (p+He) and _heavy_ (C-Fe group) components measured by KASCADE-Grande are also shown. A knee is observed in the heavy component of CRs at \(E\) = \(10^{16.92\pm 0.04}\) eV, which coincides within the uncertainties with the change of the slope in the all-particle energy spectrum around \(10^{17}\) eV. The spectral index changes from \(-\)2.76 \(\pm\) 0.02 below the knee to \(-\)3.24 \(\pm\) 0.05 above.