The proton is one of the building blocks of all matter, but its internal structure is still not well understood. Nikhef physicist Juan Rojo will explore the inner workings of the proton through an expansion of an existing experiment at CERN.
Rojo, a theoretical physicist at VU University Amsterdam and Nikhef, has received an ERC Advanced Grant of 2.5 million euros for the UNICORN project. This project will use neutrinos—generated nearby during proton collisions in the LHC accelerator at CERN—to probe the interior of protons.
Neutrinos are virtually massless particles that interact almost not at all with matter and can fly right through it. In proton collisions in an accelerator like the LHC, they are produced mainly in the directions of motion of the colliding protons.
The project represents an expansion of the existing FASER experiment, which measures neutrinos released during proton collisions in the ATLAS detector. Nikhef is indirectly involved in FASER, for example through the work of ATLAS physicist Lydia Brenner.
Since 2023, FASER has been utilizing the gentle curve of the 27-kilometer-long LHC accelerator. Neutrinos released during collisions travel in a straight line, allowing them to be measured just outside the accelerator tunnel.
FASER focuses on studying the properties of neutrinos themselves. In the proposed UNICORN project, the neutrinos are used to study the properties of protons.
It is generally known that the proton consists of three quarks (up, up, down) held together by gluons. However, quantum laws apply within the proton, allowing anti-quarks and exotic heavier quarks to appear briefly. This leads to complicated theoretical models for the proton, in which, for example, gluons may even play a decisive role.
Rojo is a specialist in the strong interaction that governs the realm of nuclear particles. Using neutrino beams from the LHC, measurements of the proton’s structure are possible, which can provide better guidance for the theory. “We want to convert FASER into a precision microscope for the proton,” he says. Artificial intelligence will be explicitly utilized in the data analyses.
The insights this yields could, for example, be important for understanding cosmic rays and cosmic neutrinos. A better understanding of the proton also improves the analyses of experiments involving proton collisions, such as those in the LHC and its more powerful successor, the HL-LHC. In these experiments, the properties of the Higgs particle are studied in detail, and the search is on for as-yet-unknown particles.
