Speaker
Description
The Pierre Auger Observatory (Auger) and the Telescope Array (TA), located, respectively, in the Southern and Northern hemispheres, are the largest ultra-high-energy cosmic ray (UHECR) observatories. The data sets of unprecedented statistics collected by the two observatories offer a unique opportunity to search for the differences between the UHECR properties in the mostly complementary sky regions. To correctly attribute such potential differences to the characteristics of the UHECR sources or propagation, the systematic effects in the measurements of each observatory should be accounted for properly. In this context, the task of the Auger-TA mass composition working group is to identify possible differences of astrophysical origin in the measurements of the depth of the maximum of air-shower profiles, $X_{\mathrm{max}}$, performed at both observatories using the fluorescence technique. Due to different approaches to event selection and analysis at Auger and TA, the working group uses a specially designed method to transfer the Auger $X_{\mathrm{max}}$ distributions into the TA detector. To this end, dedicated air-shower and detector simulations for the TA Black Rock Mesa and Long Ridge fluorescence detector stations were performed with the Sibyll 2.3d hadronic interaction model. From the comparison of the first two moments and the shapes of $X_{\mathrm{max}}$ distributions for energies above $10^{18.2}~{\rm eV}$, no significant differences between the Auger and TA measurements were found.
