Analysis of Data from the Telescope Array Observatory

University Of Utah, Salt Lake City UT

Investigators

Abstract

The Telescope Array (TA) Observatory is the largest detector of ultra-high energy cosmic rays (UHECRs) in the Northern Hemisphere. An upgrade to the observatory (TAx4) is currently underway that will double the number of deployed surface detectors (SD) over an increased total instrumented area of approximately 1800 square-km. An array of florescence detectors (FDs) overlooks this SD array, providing important additional information on the detected events. This award supports the cosmic ray physics group at the University of Utah in analysis of data from the TA Observatory. The award includes support for postdoctoral and graduate student researchers carrying out studies of the TA “hot-spots” and studies of the ultra-high energy cosmic ray spectrum and composition. Under the award, the team will continue to develop a broad outreach program, ASPIRE, that includes online web lessons and direct interactions with the local community. TA data analyses have identified a “hot-spot” of UHECRs above 57 EeV in the northern sky at 3.5 sigma significance. The observatory has also seen indications of differences in the cosmic ray spectral shape when comparing events within the hotspot region to those outside, as well as an apparent declination dependence of the spectrum at the highest energies. The source of the hotspot, however, remains unknown. Inconsistencies between the measurements of TA and the Pierre Auger Observatory, the largest UHECR detector in the southern hemisphere, are also apparent at the highest energies, including in the studies of the width and shape of the Xmax distributions. The additional data collected with the TAx4 upgrade, combined with the energy calibrations of the recently installed FDs, will improve the sensitivity of the instrument toward resolving these important open questions in our understanding of the highest energy particles in the Universe. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.