EPJ ST Highlight - Improved technique could reveal beyond standard model particles in CERN detector

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Published on 13 May 2026

A technique combining liquid thin films and machine vision could help researchers cut through the optical noise obscuring potential tracks of as-yet unobserved particles in CERN's MoEDAL detector

The Monopole and Exotics Detector at the LHC (MoEDAL) is an experiment at CERN's Large Hadron Collider (LHC), which is aiming to observe a variety of particles not described by the Standard Model. So far, however, the scope of its measurement abilities has been held back by the techniques used to measure the tracks left behind by energetic particles.

In a new study published in EPJ Special Topics (EPJ ST), Matti Kalliokoski at the University of Helsinki, Finland, presents a new approach to processing the foil used in this measurement. His method could make it far easier for researchers to detect the subtle tracks left behind by as-yet unobserved particles – potentially bringing their long-awaited measurement a step closer to reality.

To date, theoretical physicists have proposed a diverse array of particles which would require physics beyond the Standard Model to explain, including strangelets, Q-balls, dyons, and supersymmetric particles.

To search for them, MoEDAL first exposes a foil of specialised resin named CR-39 to the ionizing radiation produced during particle collisions. Afterwards, the foil is bathed, or 'etched' in a corrosive chemical, and examined under a microscope. When particles pass through the foil, they leave behind tracks of molecular damage, allowing researchers to record their paths.

CR-39 is capable of detecting tracks left by particles that ionize as weakly as oxygen ions – but in the high-radiation environment of the LHC, the foil quickly becomes saturated with tracks. During the etching process, each track creates a pit on the foil surface. With so many pits present, the surface scatters light strongly, making it especially difficult for researchers to identify the shallower, fainter pits left by less ionizing particles, including potential beyond standard model particles.

To address this problem, Kalliokoski considers how the irradiated foil could be coated in thin liquid films, with a similar refractive index to pristine CR-39. As the liquid fills the pitted surface, it smooths out the optical discontinuities responsible for scattering, allowing light to pass through the surface more cleanly and making individual pits easier to resolve. Using machine-vision techniques, researchers could then automatically detect and classify each pit by its location and size, potentially revealing the subtle traces left by as-yet unobserved particles.