CERN Detects Single Top Quark with W and Z Bosons for First Time

The CMS collaboration at CERN has achieved a significant milestone by observing the production of a single top quark in conjunction with W and Z bosons. This groundbreaking event, reported on November 3, 2025, occurs once in approximately every trillion proton collisions, marking a notable advancement in particle physics.

The phenomenon, referred to as tWZ production, provides a unique opportunity for researchers to examine the interactions of the top quark with the electroweak force, mediated by the W and Z bosons. As the heaviest known fundamental particle, the top quark’s interactions with the Higgs field are crucial for understanding fundamental forces in nature.

Complexity and Rarity of the Observation

Detecting tWZ production is exceptionally challenging due to its rarity and the complexity of the analysis involved. The process bears striking resemblance to another event known as ttZ production, characterized by the creation of a top quark and an anti-top quark along with a Z boson. Since ttZ production is approximately seven times more frequent than tWZ production, researchers face significant background noise that complicates the identification of the signal.

“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,” explained Alberto Belvedere, a researcher with the CMS collaboration at DESY. Through the use of sophisticated machine learning algorithms, the team successfully isolated the tWZ signal from the surrounding data.

Implications for Future Research

The CMS collaboration’s findings indicate that the rate of tWZ production was slightly higher than theoretical predictions. This discrepancy raises intriguing possibilities for physicists, who aim to discern whether this is a mere statistical fluctuation or a potential indication of new physics beyond the established Standard Model.

“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,” noted Roman Kogler, another researcher from the CMS collaboration.

The observation of this rare event enhances the Large Hadron Collider’s reputation as a leading facility for uncovering the fundamental secrets of the universe. As research continues, the CMS collaboration is poised to provide deeper insights into the forces that govern particle interactions and the potential for new discoveries in the realm of high-energy physics.

For more detailed information, the findings are available on the arXiv preprint server. This latest development underscores the ongoing commitment of CERN to advance our understanding of the universe at its most fundamental level.