A particle zips through silicon in billionths of a second, and the sensor manages to click, recording the exact time. This isn't science fiction; it's the result of testing the MiniCACTUS-v2 prototype at CERN in July 2025. The best result: 48.88 picoseconds — in that time, light travels just 1.5 centimeters.
The detector works like a tiny camera with pixels, but instead of light, it captures charged particles. Each pixel is a diode without internal amplification, so the signal is weak but clean. To keep it that way, all the processing electronics were moved to the edge of the chip, away from the pixels. The sensor itself was thinned to 175 micrometers — thinner than a human hair. At 500 volts, it fully depletes and collects all the charge left by the passing particle.
This level of precision is needed for experiments at future colliders, where particles collide every 25 nanoseconds. The more accurately the detector records time, the better physicists can separate events and find rare decays. MiniCACTUS-v2 is a step toward compact, inexpensive sensors that can operate in the densest particle streams. And this is just the beginning: the prototype has already shown that silicon can be faster than previously thought.
In 49 picoseconds, light travels only 1.5 centimeters — less than the width of a thumb.