Research in my group

I work in experimental particle astrophysics. I have been a member of the Pierre Auger Collaboration for over two decades (and on the process of leaving it :O( working on the detection of ultra high energy cosmic rays. I joined the HAWC Collaboration in 2009 to build a large gamma ray detector in Mexico, and I am also the PI of the AMON project at Penn State since 2013. I recently joined the GRAND Collaboration to build a giant array of radio antennas to detect ultra-high energy neutrinos.

If you are interested in any of these fantastic subjects, please read on!

Cosmic rays

We study ultra-high-energy cosmic rays -the most energetic and rare of particles in the universe. When these particles strike the Earth’s atmosphere, they produce extensive showers made of billions of secondary particles.

Grad students visiting the 1600th detector in Argentina.

While much progress has been made in nearly a century of research in understanding cosmic rays with low-to-moderate energies, rays with extremely high energies remain mysterious and detecting them is challenging because they are extremely rare.

The especially interesting cosmic rays, with energies over a hundred million times larger than those produced in the world’s most powerful particle accelerator, arrive on Earth at a rate of one per square kilometer per century. Something out there -outside of our own Galaxy- is hurling these incredibly energetic particles around the universe.

Physics at Penn State University

Discussing hardware updates in the lab.

Do these particles come from some unknown super-powerful cosmic explosion? Or from a huge black hole sucking stars to their violent deaths? Or maybe from colliding galaxies? We don’t know the answers yet, but we do know that solving this mystery will take us one step forward in understanding our universe.

Learn more about our studies of ultra-high energy cosmic rays using data from the Pierre Auger Observatory here.

Gamma rays

TeV gamma rays are markers of the most extreme environments in the known universe: supernova explosions, active galactic nuclei, and gamma-ray bursts. Gamma rays are thought to be correlated with the acceleration sites of charged cosmic rays, whose origins have been a mystery for nearly 100 years.


Undergraduate students working in the lab with photo-multiplier tubes for a water Cherenkov detector.

Cosmic rays are charged particles. We believe they are accelerated in tremendous astrophysical explosions such as supernovae, gamma-ray bursts, and the turbulent regions of space near supermassive black holes. By studying cosmic rays, we hope to gain a better understanding of these violent (and ubiquitous) objects.
High-energy gamma-ray observations are an essential tool in the study of the origins of cosmic rays, because gamma rays are created when cosmic rays interact with material near their acceleration sites. Because they are electrically neutral, the gamma rays produced in such interactions are not perturbed by the magnetic fields which fill our own galaxy and intergalactic space. Therefore, we can use them to perform gamma-ray astronomy.


Foreign exchange student working in the lab preparing a scintillator detector to enhance the detection of muons in our water Cherenkov prototype detector.

By observing the spatial distribution and intensity of gamma rays across the sky, we can attempt to identify the locations of cosmic ray accelerators. In addition, the time variability and energy spectra of the gamma-ray emission can be used to study the environment of the accelerators and the mechanisms of charged-particle acceleration. The highest-energy gamma rays (above 1 TeV) and the shortest timescales of variability provide important constraints on the mechanisms at work in acceleration sites.

Learn more about our studies of very-high energy gamma-rays using data from the High Altitude Water Cherenkov Observatory here.

Multi-Messenger Astrophysics

The Astrophysical Multimessenger Observatory Network (AMON) aims to discover new particle astrophysics phenomena by merging the world’s leading multi-messenger observatories into a single system for the first time. The facilities to be linked by AMON, collectively representing decades of effort by thousands of scientists, promise the first routine detections of extragalactic sources via “messengers” other than photons: the high-energy neutrinos of the weak interaction (the IceCube and ANTARES Neutrino Observatories), the strongly-interacting nuclei observed as cosmic rays (the Pierre Auger Cosmic Ray Observatory), and the oscillations in the fabric of space-time manifested as gravitational waves (the Advanced LIGO and VIRGO gravitational-wave detectors). These are complemented by current and next-generation gamma-ray facilities, including the Swift and Fermi satellites and the HAWC TeV gamma-ray observatory, which continuously monitor large swaths of the sky for high-energy electromagnetic phenomena. Together, the AMON partner facilities probe the high-energy universe via all four fundamental forces.

Visit our AMON pages!

Ultra-High energy neutrinos

The Giant Radio Array for Neutrino Detection (GRAND) is a planned large-scale observatory of ultra-high energy (UHE) cosmic messengers (cosmic rays, gamma rays, and neutrinos) with energies exceeding 108 GeV. The ultimate goal is to solve the long-standing mystery of the origin of UHE cosmic rays.

Three key features of GRAND will make this possible: its large exposure, sub-degree angular resolution, and sensitivity to the unique signals made by UHE particles. The strategy of GRAND is to detect the radio emission coming from the extensive air showers (EAS) that develop in the terrestrial atmosphere as a result of the interaction of UHE cosmic rays, gamma rays, and neutrinos.

prototype antenna

First antenna prototype in Northwestern China.

The design of GRAND is modular, consisting of 20 independent sub-arrays, each of 10,000 radio antennas deployed over 10,000 km2 in radio-quiet locations. A staged construction plan ensures that key techniques are progressively validated, while simultaneously achieving important science goals in UHECR physics, radioastronomy, and cosmology even during the construction stages. Already by 2025, using the first sub-array of 10,000 antennas, GRAND could discover the long-sought cosmogenic neutrinos. By the 2030s, in its final configuration, GRAND will reach an unparalleled sensitivity to cosmogenic neutrino fluxes of 4 x 10-10 GeV cm-2 s-1 sr-1 within 3 years of operation.

Because of its sub-degree angular resolution, GRAND will also search for point sources of UHE neutrinos, steady and transient. GRAND will also be a valuable tool in radioastronomy and cosmology, allowing for the discovery and follow-up of a large number of radio transients (e.g., fast radio bursts, giant radio pulses), and for precise studies of the epoch of reionization.

About me

I am a professor of physics and astronomy & astrophysics. Before joining Penn State in 2013, I was an associate professor of physics at Colorado State University. I was elected fellow of the American Physical Society in 2016. 
Teaching awards include the C. I. Noll Award for Excellence in Teaching sponsored by the Eberly College of Science Alumni Society at Penn State, Best Teacher Awards from the Colorado State University’s Alumni Association and the Student Alumni Connection, the Outstanding Mentor Award presented by the Students as Leaders in Science at the Colorado State University, and the Students Choice Award sponsored by the Associated Students of the University of Utah.
I earned my doctoral degree in Particle Physics and master’s degree in Nuclear Engineering from the Instituto Balseiro in Argentina in 2001 and 1996, respectively.

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