Antimatter research at CERN CMOS Sensors from the Smartphone for High-Energy Physics

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A team from TU Munich (Germany) has developed a high-precision detector for CERN from commercially available smartphone photo sensors. This enables the annihilation of antiprotons to be measured in real-time with sub-micrometer resolution for the first time.

With a custom-developed megapixel array based on modified CMOS camera sensors from smartphones, a team from the Technical University of Munich (TUM) provides new precision for the antimatter experiment AEgIS at CERN. The technology allows annihilation events of antiprotons to be located with micrometer accuracy—a crucial step toward measuring the gravity of antimatter.

When antimatter meets matter, annihilation occurs—a complete conversion of mass into energy, accompanied by characteristic particle tracks. The AEgIS experiment (Antihydrogen Experiment: Gravity, Interferometry, Spectroscopy) at CERN is specifically investigating how antihydrogen behaves in Earth's gravitational field. The central question: Does antimatter fall under gravity just like normal matter—or are there differences?

To detect these effects, the AEgIS team generates a horizontal beam of antihydrogen atoms. These pass through a so-called Moiré interferometer—a detector setup consisting of multiple grid structures arranged one behind the other. If antihydrogen is slightly deflected downward under the influence of Earth's gravity, the interference patterns change. The location of the subsequent annihilation—where the anti-atom interacts with matter—is the key variable for the gravitational experiments.

60 Modified CMOS Sensors

This is where the new detector OPHANIM (Optical Photon and Antimatter Imager) comes into play: a large array of 60 smartphone camera sensors, with a total of 3,840 megapixels. Developed and optimized at the FRM II research reactor of TUM, the system detects the charged pions produced during the decay with an unprecedented lateral resolution of 0.6 µm. For comparison: Previously used emulsion detectors achieved a maximum of about 20 µm, but only offline and with considerable analysis effort. In contrast, OPHANIM delivers real-time data in high resolution.

The CMOS image sensors, originally designed for mobile devices, were specifically modified: color layers and microlenses used in smartphones for image optimization were removed to use the sensor substrates directly for detecting charged particle tracks. Thanks to the submicrometer pixel density, these sensors are particularly suitable for tracking decay products with extremely short ranges.

Sensors from a Smartphone

"For AEgIS, we require detection with the highest spatial precision—CMOS sensors from smartphones provide this in a more technically and economically feasible way than many specialized detector types," explains project leader Dr. Francesco Guatieri from TUM. "The challenge was in adapting the sensors to the specific requirements of high-energy physics."

The success of this technology transfer is also due to the interdisciplinary collaboration between particle physics, microelectronics, and applied sensor technology. Master's students from the TUM School of Engineering and Design were directly involved in the development and characterization of the sensor arrays. The result is a modular detector that not only supports AEgIS but is also suitable for other applications in precision measurement and imaging techniques.

Scientific Significance of AEgIS

Gravity is so far the only fundamental interaction whose effect on antimatter has not been experimentally confirmed. A measurable difference in the free fall of antihydrogen—even in the range of a few micrometers—would raise fundamental questions about the symmetry of natural laws and the validity of the theory of general relativity. The AEgIS experiment is one of the few attempts worldwide to approach this question experimentally.

With OPHANIM, the collaboration now has a precision instrument that allows real-time tracking on a micrometer basis—with components that were originally intended for mobile camera systems. An impressive example of how consumer electronics can spur fundamental research. (heh)

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