The Standard Model of Particle Physics describes our universe at the most fundamental level. Within this theory, the visible matter of our universe consists of indivisible elementary particles known as quarks and leptons, which are divided into different types known as ‘flavors’ in particle physics. These particles interact with one another via the electromagnetic, weak, and strong forces. While this description of nature has proven highly successful, phenomena such as the predominance of matter over anti-matter and the existence of dark matter in our universe hint at new sources of physics that go beyond the Standard Model.

Belle II

In recent years, there has been a great deal of excitement worldwide about hints of new physics at special colliders known as “B Factories” that can produce an abundance of very clean collisions consisting of pairs of B mesons. PNNL is helping launch the Belle II experiment that will contribute to the investigation of these possibilities over the coming decade.

The Belle II experiment, located at the High Energy Accelerator Research Organization (known as KEK) in Tsukuba, Japan, involves an international collaboration of more than 900 researchers at 100 institutes around the world. Belle II is a specialized particle detector, three-stories tall, housing several million channels of precise radiation sensors that record the debris of electron-positron collisions. The previous Belle experiment at KEK ran from 1999 through 2010, and was used to confirm the origins of CP-symmetry breaking that was awarded the Nobel Prize in Physics in 2008. The SuperKEKB accelerator at KEK has now been updated, and the Belle detector was upgraded to the Belle II design to handle the significantly higher event rates. About 50 times as much data is expected to be collected by Belle II, allowing scientists to search for rare event types that can indicate new physics phenomena.

Data-taking at Belle II began in 2018, and hundreds of billions of these collisions will be recorded during the experiment’s lifetime. PNNL staff members are contributing their expertise in physics, detectors, electronics, and computing to this experiment. PNNL has helped build key elements of the particle identification system for Belle II, including the imaging Time-Of-Propagation (iTOP) detector optics and electronics and the KLong and Muon (KLM) detector upgrade that includes new scintillator detectors and new readout electronics.

PNNL physicists are now analyzing the newly-collected Belle II data to study the performance of the accelerator, detector, and physics performance. They plan to exploit the data to search for B meson decays producing "dark matter" particles in conjunction with baryons. These particles are not directly detectable by the Belle II experiment, but their existence can be inferred from the precise measurement of all other particles from a given collision. PNNL is also involved in the study of exotic types of particles composed of more than two or three quarks. Belle was the first experiment to discover particles made up of four quarks, extending our knowledge of subatomic matter. The larger dataset and unique collision energy capabilities of the Belle II experiment will allow scientists to further understand their nature and potentially uncover other particles of a similar nature.

As data collection from Belle II progresses into the future, PNNL will continue its efforts to further identify the large-scale implications that B meson collisions have on the subatomic matter that makes up our universe. Working alongside researchers from around the world, PNNL physicists play a key role in particle identification and data analyzation as it relates to the discovery of new physics phenomena, routinely going above and beyond the existing Standard Model of Particle Physics.

(You can read more about how High Energy Physics supports the DOE mission here.)