Scientists at CERN have made a groundbreaking discovery of an extremely rare particle decay process, paving the way for new insights into the fundamental interactions of matter.
At CERN, researchers have uncovered an exceptionally rare particle decay process, which may lead to new understandings of the fundamental interactions of matter.
Today, the NA62 collaboration showcased at a CERN EP seminar its first experimental observation of a very rare decay of a charged kaon into a charged pion alongside a neutrino-antineutrino pair (K+ → π p+νν).
This occurrence is tremendously rare — the Standard Model (SM) of particle physics suggests that fewer than one in 10 billion kaons will decay in this manner. The NA62 experiment was specifically designed and built to capture this kaon decay.
Cristina Lazzeroni, a Particle Physics Professor at the University of Birmingham, stated: “With this measurement, K+ → Ï€ p+νν ranks as the rarest decay confirmed at the discovery level — achieving the notable 5 sigma standard. This challenging analysis reflects outstanding teamwork, making me exceptionally proud of this remarkable achievement.”
Kaons are generated using a high-intensity proton beam from the CERN Super Proton Synchrotron (SPS) that collides with a stationary target. This process results in nearly a billion secondary particles being produced each second, with around 6% being charged kaons, directed into the NA62 detector. The detector accurately identifies and measures each kaon and its decay products, though neutrinos appear as missing energy.
Professor Giuseppe Ruggiero from the University of Florence remarked: “This achievement marks the end of a lengthy project that began over ten years ago. Studying natural phenomena with probabilities around 10 -11 is both captivating and challenging. Our meticulous efforts have yielded a remarkable outcome, delivering a long-awaited finding.”
The latest discovery draws from data gathered by the NA62 experiment in 2021-22, alongside a previously published result from the 2016-18 dataset. Enhanced upgrades made to NA62 enabled data collection at a 30% higher beam intensity in the 2021-22 phase with several new and improved detectors.
These hardware advancements coupled with refined analytical techniques allowed for signal candidates to be collected at a rate 50% higher than prior, while implementing new methods to reduce background noise.
A team of researchers from the University of Birmingham, currently headed by Professor Evgueni Goudzovski, has been involved with the NA62 project since its design phase in 2007, taking a key role in the collaboration.
Professor Goudzovski commented: “Our focus has always been on attracting top talent and providing leadership roles to early-career researchers. We take pride in having both the current NA62 physics coordinator and the person leading the K+ → Ï€ p+νν measurement as former PhD students from Birmingham. It is an honor to work with and lead such a dynamic and productive team.”
The research team is investigating the K+ → π p+νν decay because it could reveal new physics beyond the standard model description, making it a crucial process for identifying evidence of new physics phenomena.
The observed rate of kaons decaying into a pion and two neutrinos is approximately 13 in 100 billion, which aligns with Standard Model predictions but is about 50% higher than expected. This discrepancy may suggest the existence of new particles that enhance the probability of this decay, though further data is essential to validate this hypothesis. The NA62 experiment is actively gathering data, and researchers are optimistic about confirming or disproving the existence of new physics related to this decay in the coming years.
