Historic achievement in uncovering the fundamental forces of the universe at the Large Hadron Collider

Researchers at the University of Rochester working with the CMS Collaboration on CERNWe have made significant progress in measuring the electroweak mixing angle, which has enhanced our understanding of the Standard Model of particle physics.

Their work helps explain the fundamental forces of the universe, supported by experiments such as those at the Large Hadron Collider that delve into conditions similar to those that occurred after the great explosion.

Uncovering the cosmic secrets

In the quest to decipher the secrets of the universe, researchers from the University of Rochester have for decades participated in an international collaboration at the European Organization for Nuclear Research, known as CERN.

Building on their extensive involvement at CERN, particularly in the Compact Muon Solenoid (CMS) collaboration, the Rochester team—led by Ari Budek, the George E. Buck Professor of Physics—recently achieved a groundbreaking feat. Their breakthrough focuses on measuring the electroweak mixing angle, a key element of the Standard Model of particle physics. This model describes how particles interact and accurately predicts a wide range of phenomena in physics and astronomy.

“The recent measurements of the electroweak mixing angle are incredibly precise, having been calculated from proton collisions at CERN, and they are enhancing our understanding of particle physics,” says Buddick.

the Collaboration in CMS The CMS Collaboration brings together members of the particle physics community from around the world to better understand the fundamental laws of the universe. In addition to Bodek, the Rochester group in the CMS Collaboration includes principal investigators Regina DeMina, professor of physics, and Aran Garcia Bellido, associate professor of physics, along with postdoctoral research fellows and graduate and undergraduate students.

University of Rochester researchers have a long history of working at CERN as part of the Compact Muon Solenoid (CMS) collaboration, including playing key roles in the discovery of the Higgs boson in 2012. Copyright: Samuel Joseph Herzog; Julien Marius Urdan

CERN’s legacy of discovery and innovation

Located in Geneva, Switzerland, CERN is the world’s largest particle physics laboratory, known for its pioneering discoveries and cutting-edge experiments.

Rochester researchers have a long history of working at CERN as part of the CMS collaboration, including playing key roles in Discovery of the Higgs boson in 2012– An elementary particle that helps explain the origin of mass in the universe.

The collaboration involves collecting and analyzing data from the muon solenoid detector embedded in CERN’s Large Hadron Collider, the world’s largest and most powerful particle accelerator. The LHC consists of a 17-mile-long ring of superconducting magnets and underground accelerator structures that span the border between Switzerland and France.

The LHC’s primary purpose is to explore the building blocks of matter and the forces that govern them. It does this by accelerating beams of protons or ions to near the speed of light and colliding them with each other at extremely high energies. These collisions recreate conditions similar to those that existed just a fraction of a second after the Big Bang, allowing scientists to study the behavior of particles under extreme conditions.

Dismantling the unified forces

In the 19th century, scientists discovered that the different forces of electricity and magnetism are interconnected: a changing electric field produces a magnetic field and vice versa. This discovery formed the basis of the science of electromagnetism, which describes light as a wave and explains many phenomena in optics, as well as describing how electric and magnetic fields interact.

Building on this understanding, physicists discovered in the 1960s that electromagnetism is linked to another force—the weak force. The weak force operates inside the nucleus of atoms and is responsible for processes such as radioactive decay and powering the sun’s energy production. This discovery led to the development of electroweak theory, which postulates that electromagnetism and the weak force are actually low-energy manifestations of a unified force called the unified electroweak interaction. Major discoveries, such as the Higgs boson, have confirmed this concept.

Developments in electroweak interaction

The CMS team recently made one of the most precise measurements yet of this theory, analyzing billions of proton collisions at CERN’s Large Hadron Collider. Their focus was on measuring the weak mixing angle, a parameter that describes how electromagnetism and the weak force mix together to create particles.

Previous measurements of the electroweak mixing angle have sparked controversy within the scientific community. However, the latest results are in close agreement with expectations from the Standard Model of particle physics. Rochester graduate student Rice Taus and his postdoctoral fellow Aleko Khokhunaishvili implemented new techniques to reduce the systematic uncertainty inherent in this measurement, improving its accuracy.

Understanding the weak mixing angle sheds light on how the different forces in the universe work together on the smallest scales, deepening our understanding of the fundamental nature of matter and energy.

“The Rochester team has been developing innovative techniques to measure these electroweak parameters since 2010 and then implementing them at the LHC,” says Buddick. “These new techniques have ushered in a new era of testing the accuracy of the Standard Model’s predictions.”

The CMS Collaboration is an international scientific collaboration responsible for the Compact Muon Solenoid (CMS) experiment at CERN’s Large Hadron Collider. The collaboration brings together more than 4,000 scientists from over 200 institutions and 50 countries, conducting research in high-energy physics, exploring fundamental particles and forces, including the famous discovery of the Higgs boson in 2012.