Science & Technology (Commonwealth Union)_ Scientists at the European Organization for Nuclear Research (CERN) have made a groundbreaking observation that could open the door to new physics beyond the Standard Model. Through the NA62 experiment, researchers have detected an incredibly rare decay event involving a charged kaon, an event that, while predicted by the Standard Model of particle physics, occurred more frequently than expected, hinting at the possibility of undiscovered particles or forces in the universe.
At its core, particle physics aims to understand the fundamental building blocks of the universe by smashing particles together and analysing the resulting interactions. These collisions can provide evidence of particles and phenomena predicted by the Standard Model, such as the famous Higgs boson. However, sometimes they reveal gaps in our understanding, prompting scientists to explore the possibility of physics beyond this well-established framework.
The Standard Model and Its Gaps
The Standard Model of particle physics is a highly successful theory that describes the fundamental forces and particles in the universe. It has allowed physicists to explain a wide range of phenomena, including the behaviour of particles like protons, neutrons, and electrons. However, despite its success, the model has limitations.
There are still several unsolved mysteries, such as the nature of dark matter and the imbalance between matter and antimatter in the universe. As Professor Mark Thomson, chair of the Science and Technology Facilities Council and contributor to the NA62 experiment, noted in 2020, “The Standard Model describes the fundamental forces and building blocks of the universe. It is a highly successful theory, but there are several mysteries of the universe that the Standard Model does not explain.”
To address these gaps, physicists are searching for theoretical extensions to the Standard Model. One promising approach is studying ultra-rare processes that could reveal new particles or forces, thereby leading to a deeper understanding of the universe.
Probing Rare Kaon Decay
One such ultra-rare process being explored is the decay of a charged kaon (K+) into a charged pion (π+), along with a neutrino and an antineutrino (K+ → π+νṽ). Kaons are mesons particles made up of a quark and an antiquark composed of an up quark and an anti-strange quark. What makes them particularly interesting to physicists is that their decay is precisely predicted by the Standard Model, with fewer than 1 in 10 billion kaons expected to decay into the specified products.
The NA62 experiment at CERN was designed to detect these rare kaon decays. It works by colliding a high-intensity proton beam into a stationary target, producing secondary particles that are then detected and analysed. Neutrinos, which are nearly impossible to detect directly, are identified through the missing energy in the experiment. In 2020, the team reported initial evidence of the decay, but the new findings are even more significant.
A Historic Detection
After millions of additional collisions, including higher-energy interactions, the NA62 team has reported a 5-sigma detection of the rare kaon decay. In the world of particle physics, a 5-sigma result is the gold standard for discovery, indicating a mere 0.00006 percent chance that the result is a statistical error.
“With this measurement, K+ → Ï€+νṽ becomes the rarest decay established at discovery level the famous 5 sigma,” said Professor Cristina Lazzeroni from the University of Birmingham. “This difficult analysis is the result of excellent teamwork, and I am extremely proud of this new result.”
A Puzzling Discrepancy
While the Standard Model does predict this rare kaon decay, the NA62 team observed it occurring around 50 percent more frequently than expected about 13 times in every 100 billion decays, rather than the predicted 9. This discrepancy, though small, is highly significant. It suggests that something beyond the Standard Model might be at play, whether it be the presence of new, unknown particles or some other exotic physical process.
The possibility of new physics emerging from these results has generated excitement in the scientific community. As Professor Giuseppe Ruggiero from the University of Florence remarked, “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.”
Implications for Physics Beyond the Standard Model
This unexpected result raises several intriguing questions. What causes the higher-than-expected frequency of this rare decay? Could it be the signature of new particles that the Standard Model does not account for? Or might it point to some deeper flaw or incompleteness in the Standard Model itself?
Physicists are cautiously optimistic about the implications. “Measurements of ultra-rare processes provide an exciting avenue for exploring these possibilities, with the hope of discovering new physics beyond the Standard Model,” Professor Thomson emphasized. The discovery of a new particle or force could help explain some of the universe’s most enduring mysteries, including the elusive nature of dark matter or the reason why the universe is composed primarily of matter, despite equal amounts of matter and antimatter being created during the Big Bang.
The Future of Particle Physics
The NA62 experiment’s findings will undoubtedly prompt further research, as physicists aim to refine their measurements and explore other potential anomalies in particle decays. The next steps will likely include more high-energy collisions, deeper analysis of the data, and perhaps even the development of new theoretical models to explain the results.
In the coming years, we may witness the emergence of a new era in particle physics, one that goes beyond the Standard Model and offers new insights into the fundamental workings of the universe. With each rare event observed, scientists come closer to unravelling the mysteries that still remain proof that, in physics, even the smallest particles can reveal the most profound truths.
