A new cooling technique means the Alpha experiment at CERN's Antimatter Factory can produce antihydrogen atoms eight times faster than before.
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<p style="margin-bottom:11px">In a paper published today <em>nature communication</em>Researchers at the Alpha experiment at CERN's Antimatter Factory have reported a new technique that allows them to produce more than 15,000 antihydrogen atoms – the simplest form of atomic antimatter – in just a few hours.
“These numbers would have been considered science fiction 10 years ago,” said Jeffrey Hangst, a spokesman for the Alpha Experiment. “With large numbers of antihydrogen atoms now more readily available, we can investigate nuclear antimatter in greater detail and at a faster pace than before.”
To create atomic antihydrogen (a positron orbiting an antiproton), the Alpha Collaboration must create and trap clouds of antiprotons and positrons separately, then cool them and merge them to form antihydrogen atoms. The process has been refined and continuously improved over many years. But now, using a pioneering technique for cooling positrons, the Alpha team has increased the rate of production of antihydrogen atoms by eight times.
This spectacular progress in production rate depends on how the positrons are prepared. First, positrons are collected from the radioactive form of sodium and captured by what is known as the Penning trap, where well-coordinated electromagnetic fields keep the antiparticles in place. However, they do not remain stable. Like tigers in a zoo, positrons orbit around their cage, depleting their energy. This cools the cloud of positrons, but not so much that they can efficiently merge with antiprotons to form antihydrogen atoms. So, the Alpha team recently tried a new approach, which was to add a cloud of laser-cooled beryllium ions to the trap so that the positrons lose energy in a process called sympathetic cooling.
This brought the positron cloud to a temperature of approximately -266 °C, making it more likely that antihydrogen atoms would form when mixed with antiprotons. This approach allowed more than 15,000 antihydrogen atoms to be deposited in less than seven hours. To put this in perspective, the previous experiment took 10 weeks to collect the 16 000 antihydrogen atoms needed to measure the spectral structure of antihydrogen with unprecedented accuracy. “The new technique is a real game-changer when it comes to investigating systematic uncertainties in our measurements. We can now freeze antihydrogen overnight and measure a spectral line the next day”, said Niels Madsen, Alpha’s deputy spokesperson and leader of the positron-cooling project.
Using this approach to cool positrons, the ALPHA experiment produced more than 2 million antihydrogen atoms during the 2023–24 experimental run. And this year, researchers are using an unprecedented number of antihydrogen atoms to study the effects of gravity on antimatter as part of the Alpha-G experiment. This technique will allow even more precise measurements to be made and make it possible to investigate in depth the properties and behavior of nuclear antimatter.
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