The UHECR dipole and quadrupole in the latest data from the original Auger and TA surface detectors

PIERRE AUGER AND TELESCOPE ARRAY COLLABORATION; A. MARIAZZI

Berlin

Conferencia; 37th International Cosmic Ray Conference (ICRC2021); 2021

The sources of ultra-high-energy cosmic rays are still unknown, but assuming standard physics,they are expected to lie within a few hundred megaparsecs from us. Indeed, over cosmologicaldistances cosmic rays lose energy to interactions with background photons, at a rate depending ontheir mass number and energy and properties of photonuclear interactions and photon backgrounds.The universe is not homogeneous at such scales, hence the distribution of the arrival directions ofcosmic rays is expected to reflect the inhomogeneities in the distribution of galaxies; the shorterthe energy loss lengths, the stronger the expected anisotropies. Galactic and intergalactic magneticfields can blur and distort the picture, but the magnitudes of the largest-scale anisotropies, namelythe dipole and quadrupole moments, are the most robust to their effects. Measuring them withno bias regardless of any higher-order multipoles is not possible except with full-sky coverage.In this work, we achieve this in three energy ranges (approximately 8?16 EeV, 16?32 EeV, and32?∞ EeV) by combining surface-detector data collected at the Pierre Auger Observatory until2020 and at the Telescope Array (TA) until 2019, before the completion of the upgrades of thearrays with new scintillator detectors. We find that the full-sky coverage achieved by combiningAuger and TA data reduces the uncertainties on the north-south components of the dipole andquadrupole in half compared to Auger-only results.