Cosmic Rays

The Highest Energy Cosmic Rays

Cosmic rays were discovered just about a hundred years ago. One of the founding fathers of cosmic-ray physics is a French physicist named Pierre Auger who discovered that cosmic-rays interact with the upper atmosphere and create extended air showers of particles that can make it all the way to the ground. The higher the energy of the primary cosmic-ray, the larger the air shower. Cosmic rays impinging on our atmosphere are mostly subatomic charged particles. Until they reach the highest energies (50EeV = 50x1018eV), the distribution of arrival directions of these cosmic-rays is isotropic resulting from the scrambling of their trajectories by the galactic and extra-galactic magnetic fields (remember, these are charged particles). At the highest energies, however, it is believed that the cosmic-rays travel in relatively straight lines to the Earth, thereby opening the exciting possibility of doing charged-particle astronomy!

I am involved in both ground-based and space-based approaches to measure UHECR. I am a member of the Pierre Auger Observatory collaboration, which operate a hybrid array of detectors near Malargüe (Argentina). It is the largest ground-based observatory for UHECR in the world. I am also a member of the Extreme Universe Space Observatory (EUSO) collaboration, which aims at placing an optical telescope looking at the Earth’s atmosphere on the International Space Station (ISS). I recently joined the Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) collaboration, which looks at a way to measure UHE cosmic-rays and neutrinos from space using two satellites observing showers in stereo modes.

The work on the Pierre Auger Observatory is supported by the National Science Foundation (NSF). This funding also supports a smaller initiative called Auger@TA, which aims at comparing the responses of the Auger and Telescope Array surface detector stations. This work is performed at the TA site near Delta, UT. While the EUSO and POEMMA missions are still at the project stage, we are receiving funding from the National Aeronautics and Space Administration (NASA) to develop demonstrators to be placed on board a super-pressure balloon. The first one (EUSO-SPB1) was launched from New Zealand in April 2017. This latest effort is led by Dr. Lawrence Wiencke (see link below). A second demonstrator (EUSO-SPB2) has just been funded by NASA.