| Description |
The chemical composition of cosmic rays is critically important to understanding cosmic ray sources as well as a cosmic ray's propagation through the Galaxy and Universe. Theories explaining the features seen in the cosmic ray spectrum depend strongly on the chemical composition of cosmic rays. Composition has implications for anisotropy studies as atomic nuclei with large atomic number are more susceptible to deflection by Galactic and extragalactic magnetic fields. This work presents a composition analysis using data from the Telescope Array (TA) experiment and uses the point of shower maximum, Xmax, as the marker of a cosmic ray's chemical composition. TA is the largest cosmic ray detector in the Northern Hemisphere and makes use of both ground array as well as nitrogen fluorescence methods for detecting cosmic rays. This analysis combines both ground array and fluorescence data in a hybrid analysis to obtain resolutions of 0.5◦ in reconstructed pointing directions and 20 g/cm2 in reconstructed Xmax. Above 1018.5 eV, measured Xmax distributions using hybrid TA data are compatible with proton MC and exclude iron. However, above 1019.3 eV, the statistical power is limited and the data is compatible either proton or iron MCs. The shapes of the Xmax distributions independent of their means are compared, showing again that the data is compatible with protons and incompatible with iron. However, the statistical power for this measurement is limited above 1018.8 eV. |
