In high-energy particle physics, understanding the subatomic building blocks of matter requires precise particle identification (PID) and momentum reconstruction at particle collider facilities—such as CERN's Large Hadron Collider—and in cosmic-ray observatories. Cherenkov radiation serves as a foundation for PID systems. When a charged particle traverses a dielectric medium at a velocity exceeding the phase velocity of light within that medium ($v > c/n$, where $c$ represents the speed of light in vacuum and $n$ denotes the refractive index of the medium), it emits a coherent cone of Cherenkov photons, typically in the blue-to-ultraviolet spectrum.

To discriminate between different species of subatomic particles (e.g., kaons, pions, protons, and electrons) across specific momentum bands, experimental physics demands precise control over the refractive index $n$ of the radiator medium. Gases exhibit refractive indices marginally above unity ($n approx 1.0003$ for dry air), restricting their utility to ultra-relativistic particle velocities. Conversely, conventional liquid or solid optical media (e.g., water, optical glasses, and acrylic polymers) possess refractive indices generally exceeding 1.30. This creates a "refractive index gap" between 1.01 and 1.10, a region where naturally occurring dense solids or liquids are absent.

Synthesized optical silica aerogels bridge this refractive index gap for experimental physics. By precisely adjusting precursor concentrations during sol-gel synthesis, alongside supercritical carbon dioxide drying techniques, scientists can tune the bulk refractive index $n$ of silica aerogel continuously between 1.005 and 1.12. This tailorable index capability makes optical aerogels radiator materials in Threshold Cherenkov Detectors and Ring Imaging Cherenkov (RICH) detectors.

For deployment in particle detectors, aerogel radiators must demonstrate optical transparency in addition to precise refractive indices. Because the intensity of Cherenkov radiation generated by a single charged particle passing through a thin radiator is low, any microstructural inhomogeneities, nanoscale impurities, or macro-voids within the aerogel matrix induce severe Rayleigh scattering and photon attenuation. This scattering degrades light transmission, preventing downstream photodetectors (such as photomultiplier tubes or Silicon Photomultipliers, SiPMs) from detecting photon rings. High-energy physics grade aerogels—produced via ultra-pure precursor distillation, cleanroom synthesis, and controlled solvent extraction—minimize nanoscale density fluctuations. This process yields long Rayleigh scattering lengths across the visible and near-ultraviolet spectra, enabling Cherenkov photons to transit multi-centimeter monolithic aerogel tiles without excessive distortion.

From the Belle II experiment at the KEK accelerator complex in Japan to spaceborne cosmic-ray experiments and particle observatories worldwide, high-transparency monolithic silica aerogel tiles are deployed to identify rare physical events and subatomic species. Aerogels thus serve a key function in subatomic particle physics, acting as transparent optical elements that enable scientists to probe fundamental cosmic interactions.