Speaker
Description
The Telescope Array (TA) experiment has been observing extensive air showers (EAS) induced by ultrahigh energy cosmic rays (UHECR) since 2008. The TAx4 upgrade aims to expand the detection area of TA at the highest energies to four times its original size with 500 additional surface detectors (SD) with the nearest neighbor spacing extended from 1.2km to 2.08km. Half of the new detectors were installed in 2019, and have been operating since then. The objective of the upgrade is to significantly increase the number of events for analysis. In addition to the physical expansion, TA is also investigating improvements to its reconstruction procedure. In particular TA has previously accepted events only up to a maximum zenith angle of 55 degrees. In this paper we describe the results of extending the acceptance to 65 degrees in zenith, which required the energy estimation table to be expanded to include simulated events up to 70 degrees in zenith. To validate the accuracy of the simulation, which is crucial for both the energy estimation and for the calculation of detector acceptance, we compared distributions of key parameters between observed and simulated TAx4 data. We confirmed that there was no significant discrepancy between the two, in particular for the extended range of zenirth angles. We also show the measured TAx4 SD energy spectrum, including large zenith angle events based on three years of observation. Finally, we applied the extension to the TA SD analysis, generating a new energy estimation table for zenith angles up to 70 degrees. We also compared the observed and simulated TA SD data and validated the method.
| Collaboration(s) | Telescope Array experiment |
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