CMS Collaboration Achieves First Observation of Single Top Quark

The *CMS collaboration* at CERN has made a groundbreaking observation by detecting the production of a single top quark in conjunction with a W and a Z boson. This rare event, known as tWZ production, occurs only once in every trillion proton collisions at the *Large Hadron Collider (LHC)*. The significance of this discovery not only enhances our understanding of fundamental forces but also opens pathways for potential new physics.

Understanding the Significance of tWZ Production

In particle physics, the top quark is recognized as the heaviest known fundamental particle. Its interactions with the *Higgs field* can provide insights into the Higgs mechanism, which is crucial for understanding mass generation in elementary particles. The tWZ process allows physicists to explore how the top quark interacts with the electroweak force, transmitted by the W and Z bosons.

The observation is akin to finding a needle in a haystack the size of an Olympic stadium. The complexity of the tWZ production event is compounded by its similarity to another process, known as ttZ production, where a top and an anti-top quark are produced alongside a Z boson. The ttZ process occurs approximately seven times more frequently than tWZ production, which introduces significant background noise that must be distinguished to confirm the findings.

Advanced Techniques in Data Analysis

To tackle the challenges of identifying this rare event, the CMS collaboration employed advanced analysis techniques, incorporating state-of-the-art machine learning. According to *Alberto Belvedere*, a researcher with the CMS collaboration at *DESY*, “Observing tWZ production requires advanced analysis techniques involving state-of-the-art machine learning.” This innovative approach enabled researchers to effectively separate the tWZ signal from the background data.

The findings, which were released on November 3, 2025, indicate that the rate of tWZ production is slightly higher than theoretical predictions. This discrepancy raises intriguing questions about the potential existence of unknown interactions or particles. As noted by *Roman Kogler*, also a researcher with the CMS collaboration at DESY, “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.”

The observation of this phenomenon confirms the LHC’s ongoing capability to uncover the most elusive secrets of nature, marking a significant milestone in particle physics research. Future analyses and additional data will determine whether the observed rates represent a statistical anomaly or an indication of new physics beyond the established Standard Model.

The results are available on the *arXiv* preprint server, providing a resource for further exploration of this groundbreaking discovery. As the CMS collaboration continues its investigations, the implications of tWZ production may lead to deeper insights into the fundamental structure of matter and the forces that govern the universe.