Auger at Telescope Array (Auger@TA) Surface Detector Cross-Calibration

Auger@TA is a joint experimental in-situ cross-calibration of the surface detector (SD) stations used by the two largest ultra-high energy cosmic-ray (UHECR) observatories, Pierre Auger Observatory (Auger) in the southern hemisphere and the Telescope Array (TA) in the northern hemisphere. In both collaborations, the SD is the statistical engine which is used to measure the cosmic-ray energy spectrum. These measurements differ noticeably at the highest energies, within the limits of their systematic uncertainties. The two observatories utilize SD station detection media which have different response sensitivities to the components of an UHECR extensive air shower. The initial phase of the program has co-located Auger and TA SD stations within the TA site to perform a direct comparison of these two SD types which underpin important measurements. Data taking is ongoing, comparing station responses for high energy showers which pass the TA SD trigger. Preliminary results are presented and compared to simulation results using the TA reconstruction parameters. The second phase of the program will deploy six additional Auger SD stations in a small array, allowing direct in-situ comparison of the two shower measurement and reconstruction methods.