  The Cherenkov effect enables a valuable tool, known as the Cherenkov
detector, to identify high-energy particles via the measurement of the
Cherenkov cone. However, the sensitivity and momentum coverage of such
detectors are intrinsically limited by the refractive index of the host
material. Especially, identifying particles with energy above multiple
gigaelectronvolts requires host materials with a near-unity refractive index,
which are often limited to large and bulky gas chambers. Overcoming this
fundamental material limit is important for future particle detectors yet
remains a long-standing scientific challenge. Here, we propose a different
paradigm for Cherenkov detectors that utilizes the broadband angular filter
made from stacks of variable one-dimensional photonic crystals. Owing to the
Brewster effect, the angular filter is transparent only to Cherenkov photons
from a precise incident angle, and particle identification is achieved by
mapping each Cherenkov angle to the peak-intensity position of transmitted
photons in the detection plane. This unique property of the angular filter is
exceptionally beneficial to Cherenkov detection as it enables the realization
of a non-dispersive pseudo refractive index over the entire visible spectrum.
Moreover, such a pseudo refractive index can be flexibly tuned to arbitrary
values, including those close to unity. Our angular-selective Brewster paradigm
offers a feasible solution to implement compact and highly sensitive Cherenkov
detectors especially in beam lines and it can cover a wide momentum range using
readily available dielectric materials.
