CERN Experiment Report Strong Evidence Of Extremely Rare Decay Event

The NA62 experiment in a wide-angle photo. CERN

Over the last 100 years, particle physics has pushed our understanding of the natural world to greater and greater depths. More and more, we are seeing the limitations of the leading theories, so to probe what’s beyond our current understanding, scientists look at the rarest of events.

Among them, there is a particular particle decay that only happens a handful of times for every trillion. The particle in question is known as a kaon. While the proton and neutrons at the center of the atoms that make us are composed of three quarks, kaons are instead composed of two. These particles are created in an accelerator but they are also raining down on all of us as we speak in the form of cosmic rays. Physicists are particularly interested in these kaons because the pesky little particles have been caught violating several physics conservation laws – and that’s always exciting.

The hope was that in the extremely rare decays, some effect of exotic physics will become apparent. The NA62 experiment at CERN looked at exactly that and they now report on the analysis of two years' worth of data. The team did indeed see this extremely rare kaon decay, where the kaon turns into a pion (another two-quark particle) and two neutrinos.

Out of 6 trillion kaon decays, the team detected 17 of these particular events. The results were measured to a 30 percent precision and are broadly consistent with the Standard Model of Particle Physics.

“This kaon decay process is called the ‘golden channel’ because of the combination of being both ultra-rare and excellently predicted in the Standard Model. It is very difficult to capture and holds real promise for scientists searching for new physics,” Professor Cristina Lazzeroni, a particle physicist at the University of Birmingham and spokesperson for NA62, said in a statement.

“This is the first time we have been able to obtain significant experimental evidence for this decay process. It is an exciting moment because it is a fundamental step towards capturing the precise measurement of the decay and identifying possible deviations from the Standard Model.”

The collaboration is planning to collect more data from next year until 2024. The experiment is being upgraded and more data will be available. The larger data set will hopefully push the precision to around 10 percent. Currently, it is unknown if this will be enough to see a deviation from the Standard Model, but researchers are already working on ways to push that precision even further and catch more glimpses of what’s beyond our physics theories.


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