Reviewed by Danielle Ellis, B.Sc.Sep 25 2024
Researchers at CERN have uncovered a decay process for extremely rare particles, providing a new avenue for the search for physics beyond the interaction of matter's constituent elements.
The first experimental observation of the ultra-rare decay of the charged kaon into a charged pion and a neutrino-antineutrino pair (K+ → πp + νν) was presented today by the NA62 collaboration at a CERN EP seminar.
This is an extremely uncommon event; according to particle physics' Standard Model (SM), which describes how particles interact, fewer than one in ten billion kaons will decay in this manner. To measure this kaon decay, the NA62 experiment was specifically designed and built.
With this measurement, K+ → π p + νν becomes the rarest decay established at discovery level - the famous 5 sigma. This difficult analysis is the result of excellent teamwork, and I am extremely proud of this new result.
Cristina Lazzeroni, Professor, Particle Physics, University of Birmingham
When a high-intensity proton beam from the CERN Super Proton Synchrotron (SPS) collides with a stationary target, kaons are created. This produces a secondary particle beam that enters the NA62 detector at a speed of nearly one billion particles per second, of which roughly 6% are charged kaons. Except neutrinos, which manifest as missing energy, the detector precisely detects and measures every kaon and its decay products.
This is the culmination of a long project started more than a decade ago. Looking for effects in nature that have probabilities to happen of the order of 10 -11 is fascinating and challenging. After rigorous and painstaking work, we have got a stunning reward to our effort and delivered a long-awaited result.
Giuseppe Ruggiero, Professor, University of Florence
The new result is based on a combination of data from the 2016–18 dataset and data collected by the NA62 experiment in 2021–2022. After a series of modifications to the NA62 configuration that enabled operation at 30% higher beam intensity with multiple new and enhanced detectors, the 2021–22 dataset was gathered.
Improvements in hardware coupled with improved analysis methods allowed for a 50% increase in the rate of signal candidate collection while introducing additional tools for background suppression.
In 2007, a team of scientists from the University of Birmingham, under the direction of Professor Evgueni Goudzovski, joined the NA62 experiment during the design stage and became a key member of the team.
Attracting top talent and offering positions of responsibility to early-career researchers has always been the priority for the group. We are proud that both the current NA62 physics coordinator and the current convener of the K+ → π p + νν measurement are former Birmingham PhD students. It is a privilege to work in and lead such an energetic and constructive team.
Evgueni Goudzovski, Professor, University of Birmingham
The K+ → π p + νν decay is highly sensitive to new physics beyond the SM description, and the research team is examining it. Because of this, decay is one of the most intriguing processes for examining for proof of novel physics.
It is estimated that roughly 13 in 100 billion kaons decay into a pion and two neutrinos. Although this number is roughly 50% higher, it matches SM's predictions. This might be because new particles make this decay more likely, but further evidence is required to support this theory. Within the next few years, scientists hope to either confirm or rule out the presence of new physics in this decay, which is currently being monitored by the NA62 experiment.