CERN Finds New Evidence of Ultrarare Process That Could Explain Dark Matter

Scientists at CERN have reported finding evidence for a process previously predicted by theory. The ultrarare process could lead to new physics regarding particle processes, explaining dark matter, and answering cosmological questions.

CERN's NA62 collaboration is a project supported by the UK Science and Technology Facilities Council (STFC) and includes scientists from the Universities of Birmingham, Glasgow, Bristol, and Lancaster. They have presented their report at the recent ICHEP 2020 conference in Prague. The project has yielded its first significant experimental evidence of a charged kaon decaying into a charged pion and two neutrinos (K+ → π+νν).

Beyond the Standard Model

Decay processes are important in advancing physics research because of their sensitivity towards deviation from theoretical predictions. Moreover, kaon decays have been identified as an essential testing ground for the electroweak flavor theory, which could offer an alternative theoretical model in particle physics.

Since the 1970s, particle physics has mostly relied on the Standard Model. It has described three of the four fundamental forces, not including the gravitational force. As a result, it does not illustrate recent discoveries such as dark matter and the origin of the matter-antimatter imbalance. Proof of the charged kaon decay could lead to new physics and a new model beyond the Standard Model.

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Professor Mark Thomson, STFC Executive Chair and particle physicist, said, "physicists have been searching for theoretical extensions to the Standard Model. Measurements of ultra-rare processes provide an exciting avenue for exploring these possibilities, with the hope of discovering new physics beyond the Standard Model."

The Golden Channel

In a September 2019 report from the University of Birmingham, Particle Physics Professor Cristina Lazzeroni called the kaon decay process "the golden channel," owing to its combination of being ultrarare and excellently predicted in the Standard Model.

Lazzeroni added: "By capturing a precise measurement of the decay, we can identify deviations from the Standard Model prediction. The new result has still limited statistics but has already enabled us to begin putting constraints on some new physics models."

Measurements of kaon decay have been led by STFC Ernest Rutherford Fellow Dr. Giuseppe Ruggiero, from Lancaster University, since 2016. In the ICHEP report, Dr. Ruggiero admitted to the challenge of suppressing a large amount of unwanted data without losing the information they wanted to detect.

NA62 Findings

The NA62 experiment was first approved in 2007 and started its data gathering in 2015. Located in the North Area of the CERN SPS accelerator, NA62 was specifically designed to probe kaon decays. The Prevessin site in France provided the data, taken between 2016 to 2018.

Researchers poured through an equivalent exposure of 6×1012 kaon decays in the period. Owing to the ultrarare process, researchers isolated the target signal through the blind analysis technique.

They don't conduct observation in the "blind box" region, where the kaon decay is supposed to be. Instead, they observe the background in verifying their experiments. They later look at the blind box. From the 2018 dataset, the experiment yielded 17 charged kaon events--a significant excess from their expected background of 5.3 events.

The next event reportedly includes a high-intensity kaon beam to inquire about the analogous decay of the neutral kaon to pion and neutrinos.

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