Studying the Efficiency of Telescope Array TAx4 Surface Detectors Through the Artificial Expansion of TAx4

Ultrahigh energy (UHE) cosmic rays are the most energetic particles known in nature, eclipsing those produced at accelerators by humans by a factor of more than a million.

The Telescope Array (TA) Project is an experiment designed to measure the arrival direction and energy of these particles by utilizing the largest array of scintillator detectors in the

northern hemisphere.

The TA began data collection in 2008 with an original surface detector (TA SD) array composed of 507 detectors with 1.2 km of spacing, organized in a square grid. Due to the observation of potential sources, the collaboration planned to expand the array by an additional 500 detectors with larger spacing. The expansion, known as TAx4, would quadruple the original aperture of the array.

The first 257 of the TAx4 detectors were deployed into the field in 2019. However, COVID intervened and the remaining detectors were delayed due to the pandemic.

To better understand the efficiency of the expansion array we artificially split up the original TA SD array into two checkerboarded SD arrays. This artificially expands the spacing of our detectors to 1.7 km which is closer to the 2.08 km of the TAx4 array. This allows us to study the reconstruction efficiency and analysis of the data at larger detector spacing.