Physicists Find Evidence Of Rare Beauty Particle Decay

A Breakthrough In Particle Physics

Physicists from the University of Warwick, as part of a UK-led international team, have uncovered the first evidence of an exceptionally rare decay process involving a beauty particle. This achievement comes after a dedicated scientific pursuit that began in 1984. The findings were produced using the upgraded LHCb experiment at CERN’s Large Hadron Collider, with critical support provided by the Science and Technology Facilities Council.

Beauty particles are generated in immense quantities within the collider, yet they are incredibly short-lived, existing for only about one and a half trillionths of a second before they break apart. By studying the specific ways these particles decay, scientists can explore a realm known as the Zeptoverse. This microscopic world, measuring a billionth of a trillionth of a metre across, is believed to be a place where undiscovered particles and forces may reside. Understanding these forces is essential for solving some of the greatest mysteries in science, including the nature of dark matter.

Probing The Zeptoverse

The specific decay event identified by the team involves a beauty particle transforming into two muons, a process referred to as Bd to mu mu. This particular transition is predicted to occur in only one out of every ten billion beauty particles, making it one of the rarest events ever observed at the facility. Because such rare decays are highly sensitive to the influences of the Zeptoverse, detecting them allows physicists to test the limits of current scientific understanding.

Capturing this evidence required the team to isolate a very faint signal from a massive amount of background noise. To achieve this, researchers combined data from 2011 to 2018 with new data collected in 2024 and 2025. The detection process was significantly enhanced by a detector capable of recording collisions at five times the rate of previous iterations. Additionally, the team employed machine learning techniques to sharpen their search and improve the precision of the results.

Professor Tim Gershon from the University of Warwick, who leads the LHCb experiment, noted that the result demonstrates the extraordinary ability of the equipment to probe nature at its most fundamental level. He emphasized that the project is producing high-quality science and highlighted the importance of planned upgrades for the 2030s to continue this journey of discovery.

Statistical Significance And The Standard Model

The current result has a statistical significance of 3.2 sigma. In the world of physics, this level of significance is sufficient to be classified as evidence, although it has not yet reached the five-sigma threshold required to be officially labeled a discovery. Despite this, the findings align with the Standard Model, which is the leading theoretical framework for fundamental particles. This alignment is helpful for scientists as it narrows the search for signs of new physics that might exist beyond the current model.

Dr. Harry Cliff, an Ernest Rutherford Fellow at the University of Cambridge and leader of the analysis team, described the experience of finding a particle decay that had been sought since before his birth as a privilege. He suggested that the scientific community is now knocking on the door of the Zeptoverse and expressed anticipation for deeper exploration.

The United Kingdom has provided the most significant contributions to the upgraded detector. Key components include the RICH system used for particle identification and the silicon Vertex Locator, which is positioned just five millimetres from the beams of the collider. Looking forward, another major upgrade scheduled for the 2030s is expected to increase the rate of data collection by another factor of five, potentially leading to the definitive discovery of even rarer phenomena.