CMS Collaboration Discovers Rare Single Top Quark Production

The CMS collaboration at CERN has made a groundbreaking discovery by observing the production of a single top quark along with a W and a Z boson. This remarkable event, known as tWZ production, occurs only once every trillion proton-proton collisions at the Large Hadron Collider (LHC), highlighting the extraordinary capabilities of this research facility.

Unveiling the Fundamental Forces

Finding this specific event in the vast data generated by the LHC is akin to searching for a needle in a haystack the size of an Olympic stadium. The observation opens new avenues for understanding the fundamental forces of nature, particularly how the top quark interacts with the electroweak force, which is mediated by the W and Z bosons. As the heaviest known fundamental particle, the top quark also interacts most strongly with the Higgs field, making the tWZ process a key area for potential discoveries.

Studying the tWZ production could lead to insights into the Higgs mechanism and possibly reveal signs of new physics beyond the established Standard Model. Despite its significance, observing tWZ production presents substantial challenges. The process is not only one of the rarest Standard Model events detectable at the LHC but also bears great resemblance to the more common ttZ production, where a top and an anti-top quark are produced alongside a Z boson. This competing process occurs approximately seven times more frequently than tWZ production, creating considerable background noise that researchers must meticulously sift through.

Advanced Techniques for Complex Analysis

“Because of its rarity and its similarity with the ttZ process, observing tWZ production requires advanced analysis techniques involving state-of-the-art machine learning,” stated Alberto Belvedere, a researcher with the CMS collaboration at DESY. The team utilized a sophisticated machine learning algorithm to successfully differentiate the signal from tWZ production amidst the background data.

Preliminary findings indicate that the rate of tWZ production is slightly higher than theoretical predictions. This discrepancy raises intriguing possibilities for future research. “If there are unknown interactions or particles involved, the observed deviation between the measured rate of tWZ production and the prediction would rapidly become larger with increasing energies of the outgoing particles, an effect that is unique to the tWZ process,” explained Roman Kogler, also a researcher with the CMS collaboration at DESY.

The discovery, announced on November 3, 2025, marks the first observation of this rare phenomenon, reinforcing the LHC’s role in advancing our understanding of the universe’s fundamental structure. The findings are documented on the arXiv preprint server for further review and analysis, inviting the global scientific community to explore the implications of this significant breakthrough.

As researchers continue to analyze the data, the potential for uncovering new physics remains a tantalizing prospect, further emphasizing the LHC’s capacity to reveal nature’s most elusive secrets.