Assistant Professor Jesse Liu led a team turning the Large Hadron Collider (LHC) into a cosmic-ray laboratory. On April 8th, 2026, ATLAS released the world's first measurements of proton-oxygen collisions. The new interdisciplinary results are highly anticipated by astronomers to help unravel mysterious cosmic-ray showers raining from the sky.
Cosmic rays are high-energy particles from space that constantly bombard Earth. When cosmic rays hit the atmosphere, showers of particles rain down from the sky. Today, astronomers actively research where cosmic rays come from, what they are made of, and even their role in the origins of life on Earth. Despite these mysteries, cosmic rays already find fascinating applications from imaging volatile volcanoes to ancient Egyptian pyramids.
NYU has a long history of experimental cosmic-ray research. In the mid-twentieth century, a vibrant group included Serge Korff, Rosalind Mendell, and Nobel laureate Frederick Reines, which grew into the NYU Cosmic Ray Project. This period was a golden age in cosmic-ray discoveries, from new subatomic particles to carbon dating revolutionizing archaeology. More recently, NYU faculty members Allen Mincer and Peter Nemethy led the MILAGRO experiment in New Mexico, observing cosmic flashes of light called gamma rays.
Jesse joined this storied research community as an Assistant Professor in 2025, who reflects "it is fitting that my research continues a long tradition of cosmic-ray science in New York. Joining activities at NYU’s interdisciplinary Center for Cosmology and Particle Physics, I see the exciting interplay with research by my astronomy colleagues."
Astronomers rely on computer simulations of cosmic-ray showers to interpret their telescope observations. However, a longstanding problem is that these simulations are inaccurate and models disagree significantly with one another. These obstacles arise from calculations of the strong force being notoriously difficult. To improve their accuracy, physicists need to place cosmic rays under the microscope.
Before arriving in New York, Jesse was a research fellow at Trinity College in the University of Cambridge, UK. There he explored unconventional ideas to zoom into these cosmic collisions with the ATLAS experiment, leading discussions at the Standard Model Workshop at Prague in 2023 and organizing LHC Forward Physics Workshops at CERN, Switzerland in 2024. In July 2025, ideas became reality: scientists at CERN pioneered protons colliding with oxygen nuclei.
"For the first time, collisions of the sky are recreated in the comfort of the lab. The proton beam acts as the cosmic ray while the oxygen nucleus mimics the atmosphere", explains Jesse. He joined a core analysis team of particle physicists Lydia Beresford and Savannah Clawson at DESY Hamburg, Cigdem Issever and Clara Leitgeb at Humboldt University in Berlin, and Ynyr Harris at Bonn University who announced the results this week at the SM@LHC Conference in Torino, Italy.
In this team, Jesse spearheaded studies of the detector, data analysis design, and model simulation. A landmark result reported in their arXiv preprint paper is the proton-oxygen interaction rate called cross section. This measurement relied on a key ingredient called luminosity determined by collaborating with nuclear physicists Kartik Bhide at Freiburg University and Brian Cole at Columbia University. The results cross disciplines by enabling direct comparison with data by astronomers.
"CERN is famous for discovering the Higgs boson that inspired me to study particle physics as a graduate student. This new result shows the fruitfulness of interdisciplinary collaboration and thinking outside the box to start an exciting astroparticle program at ATLAS", says Jesse.
Transforming the LHC into a cosmic-ray microscope opens a new window on particles high up in the sky. These results also establish cross-disciplinary research with nuclear and astroparticle physicists to unravel the secrets of our universe.