Image caption: The new AEgIS detector (left) and a selection of the antiproton annihilations it captured (right). Annihilations appear as star-shaped events with multiple tracks emanating from one primary vertex. Green, cyan and orange arrows point to examples of nuclear fragments. (Image: AEgIS/CERN)
Did you know that the camera sensor in your smartphone could help unlock the secrets of antimatter? The AEgIS collaboration, led by Professor Christoph Hugenschmidt's team from the research neutron source FRM II at the Technical University of Munich (TUM), has developed a detector using modified mobile camera sensors to image in real time the points where antimatter annihilates with matter. This new device, described in a paper just published in Science Advances, can pinpoint antiproton annihilations with a resolution of about 0.6 micrometres, a 35-fold improvement over previous real-time methods.
AEgIS and other experiments at CERN's Antimatter Factory, such as ALPHA and GBAR, are on a mission to measure the free-fall of antihydrogen within Earth's gravitational field with high precision, each using a different technique. AEgIS's approach involves producing a horizontal beam of antihydrogen and measuring its vertical displacement using a device called a moiré deflectometer that reveals tiny deviations in motion and a detector that records the antihydrogen annihilation points.
"For AEgIS to work, we need a detector with incredibly high spatial resolution, and mobile camera sensors have pixels smaller than 1 micrometre," says Francesco Guatieri, the principal investigator on the paper. "We've integrated 60 camera sensors into our detector, enabling it to achieve a resolution of 3840 mega pixels - the highest pixel count of any imaging detector to date."
Previously, photographic plates were the only option, but they lacked real-time capabilities," added Guatieri. "Our solution, demonstrated for antiprotons and directly applicable to antihydrogen, combines photographic-plate-level resolution, real-time diagnostics, self-calibration and a good particle collection surface, all in one device."
The researchers used commercial optical image sensors that had previously been shown to be capable of imaging low-energy positrons in real time with unprecedented resolution. "We had to strip away the first layers of the sensors, which are made to deal with the advanced integrated electronics of mobile phones," says Guatieri. "This required high-level electronic design and micro-engineering."
A key factor in achieving the record resolution was an unexpected element: crowdsourcing. "We found that human intuition currently outperforms automated methods," says Guatieri. The AEgIS team asked their colleagues to manually determine the position of the antiproton annihilation points in each of the more than 2500 detector images, a procedure that turned out to be far more accurate and precise than any algorithm. The only downside: it took up to 10 hours for each colleague to plough through every annihilation event.
"The extraordinary resolution also enables us to distinguish between different annihilation fragments," says AEgIS spokesperson Ruggero Caravita. By measuring the width of tracks of different annihilation products, the researchers can investigate whether the tracks are produced by protons or pions.
"The new detector paves the way for new research on low-energy antiparticle annihilation, and is a game-changing technology for the observation of the tiny shifts in antihydrogen caused by gravity," says Caravita.
