On Friday, after a three-year maintenance phase, the first proton beams were again put into circulation by the particle accelerator at the European Organization for Nuclear Research (Cern) in Geneva. As planned, they circulated in the opposite direction in the 27-kilometer underground ring, as the research director of the European Organization for Nuclear Research (Cern), Joachim Mnich, said. Because of a corona infection, he was only able to follow this from domestic isolation.
It now takes six to eight weeks for the machine to run at full speed. Then proton collisions take place again, which are supposed to reveal insights into the basic laws of the universe. The two proton beams initially circulate with an injection energy of 450 billion electron volts. For collisions, the energy is ramped up to 13.6 trillion electron volts.
The particle accelerator is used to simulate the time when the universe came into being around 14 billion years ago. Researchers observe the decay processes during the collisions and gain insights into the smallest components of matter, the elementary particles. Among other things, the Higgs boson, which was theoretically described 40 years earlier, was detected for the first time at CERN in 2012. It contributes to the fact that elementary particles have a mass.
The data is created in milliseconds, the evaluation takes years
During the shutdown, the performance of the accelerator and the detectors connected to it has been significantly increased. It will now run for four years. “We hope to double the number of collisions since the particle accelerator went into operation by the end of 2025,” says Mnich. The accelerator has already gone through two phases of operation: from 2009 to 2012 and from 2015 to 2018.
According to Mnich, around 1,000,000,000,000,000 – one quadrillion – collisions should be possible every year. But only one in perhaps 100,000 collisions reveals processes that are worth closer analysis. The data about what happens is stored within milliseconds, but the evaluation often takes years.
This was the case at the US research center for particle physics Fermilab, which came up with a sensation at the beginning of April: From data more than ten years old, physicists had recalculated the W boson, which transmits one of the four fundamental forces that determine the behavior of matter in the universe. The researchers determined with great precision that it is heavier than predicted by the Standard Model of particle physics with its twelve matter particles and their interaction. These results have not yet been confirmed.
“We can only congratulate our colleagues at Fermilab,” says Mnich. The W boson was discovered at CERN in 1983. He assumes that the American measurements can be confirmed or disproved here in the next four years. “If the result is correct, this could be an indication of an unknown force in nature, or an indication of additional particles that we do not yet know.”
An anomaly that deviates from the Standard Model of particle physics was also discovered at CERN last year in a completely different context. Beauty quarks did not decay into muons and electrons in equal parts, as expected. With much larger amounts of data, physicists are now hoping for new insights that could raise even more questions about the validity of the Standard Model.