Speaker
Description
The Pierre Auger Observatory has been collecting data for over 19 years, reaching more than $123\,000\,\text{km}^2\,\text{sr}\,\text{yr}$ of accumulated exposure, with the surface detectors spread over $3\,000\,\text{km}^2$. The most significant discovery to this date is a large-scale dipole structure with a total amplitude of approximately $7\%$. This results from the observed modulation in right ascension in the inclusive energy bin above $8\,$EeV, where the computed dipole equatorial component has a statistical significance of $6.8\sigma$. A similar dipole pattern in the events with energies between $8$ and $16\,$EeV has recently been observed with a statistical significance of over $5\sigma$. The Pierre Auger Collaboration has also reported an increase in the dipole amplitude with energy. This anisotropy is understood to be of extragalactic origin, as the maximum of the dipole points to a direction $\sim115^\circ$ away from the Galactic center. In the same energy range, the observed evolution of the depth of maximum shower development with energy indicates a progression towards heavier composition of cosmic rays with increasing energy. This contribution presents a novel approach to a search for composition-enhanced large-scale anisotropy. On the one hand, lighter events have higher rigidity than their heavier counterparts; therefore, their trajectories are less affected by the Galactic and extragalactic magnetic fields. The expected effect is a higher anisotropy in the arrival direction of a subset of events with smaller mass and charge than the anisotropy in the overall flux of cosmic rays. On the other hand, the attenuation length is distinct for each mass group, leading to different horizons of cosmic ray sources for light and heavy particles at a given energy. Under a source-agnostic model, we investigate the dipole amplitude as a function of rigidity. Using a simulation library, we analyze the possibility of measuring a separation in total dipole amplitude between two $A$-distinct sub-populations of the Auger Phase I dataset.
