Using the Pierre Auger Observatory, the largest cosmic ray detector ever built, we study ultra-high energy cosmic rays (UHECRs), the most energetic particles in the universe. When these rare particles strike the atmosphere, they produce extensive air showers made of billions of particles. While cosmic rays with low to moderate energies are well understood, those with extremely high energies remain mysterious.
Our group has actively participated in the construction of the Auger Observatory. In particular, on the design, construction, and operation of the four LIDAR stations and the two laser facilities. We have also participated in different components of the atmospheric monitoring system, and the relative and absolute calibrations of the fluorescence detectors. For the operation of the Observatory, we are responsible for maintaining the laser systems at the site.
Our first contributions to the data analysis concentrated mainly on atmospheric monitoring and on the reconstruction of hybrid events. Hybrid events are ultra-high energy comic ray showers seen simultaneously by both the surface array and the fluorescence detectors. The main advantages of using hybrid events are: the better angular reconstruction, the reach to lower energies, and the measurement of the longitudinal development of the showers. We have developed the geometrical reconstruction of hybrid events. Hybrid events are used for anisotropy studies (searches for Galactic sources, for example), composition measurements (setting limits to photon primaries, measuring the the elongation rate), and for the determination of the primary spectrum (extended to lower energies).
Our current efforts focus on the searches for anisotropy at both ends of the energy range available to us. At the highest energies, the data set from the Auger Observatory is unique. The magnetic deflections of the highest energy cosmic rays should be small enough that allow us to do astronomy with charged particles! We study possible correlations between the arrival directions of the UHECRs with the distribution of nearby matter.
The lower energy end of the Auger data set is also interesting because it is where the transition from Galactic to Extra-Galactic origin is expected to occur. We study the phase of the right ascension distribution as a function of energy as a smoking gun of a dipole distribution that changes orientation. We also search for possible Galactic sources of UHE neutrons. We are extending this analysis to include data taken with the Infill array. This smaller array has water Cherenkov detectors at half the distance of the regular Auger array. Thus, the Infill array gives us access to lower energy cosmic rays than the originally designed Auger surface array.
If you are interested in the work of our group, you can read more in these papers:
- “Constraints on the origin of cosmic rays above 1018 eV from large scale anisotropy searches in data of the Pierre Auger observatory,” The Astrophysical Journal Letters 762 (2013) L13 [arxiv:1212.3083]
- “A Search for Point Sources of EeV Neutrons,” The Astrophysical Journal 760 (2012) 148 [arxiv:1211.4901]
- “Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter,” Astroparticle Physics 34 (2010) 314–326 [arxiv:1009.1855]
This material is based upon work supported by the National Science Foundation under award number PHY-1068210. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.