Published: July 5, 2012

An international team including University of Colorado Boulder researchers has found the first direct evidence for a new particle that likely is the long sought-after Higgs boson, believed to endow the universe with mass.

Comprised of thousands of scientists, students and support staff working at the European Organization for Nuclear Research, or CERN, the team has been conducting experiments at a facility known as the Large Hadron Collider, a $10 billion, 17-mile underground loop below the Swiss-French border in Geneva that is the world’s most powerful atom smasher. Scientists have been using the LHC to attempt to recreate conditions immediately following the Big Bang by smashing protons together, searching for answers about dark matter, dark energy, gravity and the fundamental laws of physics.

A huge target of the LHC effort has involved looking for evidence of the elusive Higgs boson, a theoretical elementary particle that has been predicted by physicists. Thought to give other elementary particles their mass, the Higgs boson is the only particle predicted by the Standard Model of particle physics -- a scientific theory of how the universe works at the simplest level -- that has not been directly detected. 

The CERN team is reporting evidence today of an anomalous “bump” in a particular search region of the energy spectrum targeted by the scientists that has a mass of about 125 billion electronic volts, or 125 GeV, said CU-Boulder physics Professor John Cumalat. The research team designed their searches around the theoretical expectations for the decay of the Standard Model Higgs boson particle, he said.

“What we have found is incontrovertible evidence for a new particle at around 125 GeV,” Cumalat said. “To prove it is the Standard Model Higgs particle we will need to carefully measure the new particle’s properties, but with more data these properties can be determined.”

The CU-Boulder high-energy physics team, which includes 15 faculty and students, is involved with the Compact Muon Solenoid, or CMS, one of two massive particle detectors in the LHC and which weighs more than 12,500 tons. The CU team helped design and build the CMS forward pixel detectors -- the “eyes” of the device -- that help researchers measure the direction and momentum of subatomic particles following collisions, providing clues to their origin and structure. 

CU-Boulder Professor William Ford said there were strong hints of the existence of the Higgs boson particle during the CMS particle collisions in 2011. “Now, with the new data looking so similar, it's hard not to be a believer,” he said. The CERN team hopes to accumulate about four times as much data as they have now on the Higgs boson search project by the end of the year, according to Ford.

While the Higgs boson was nicknamed “The God Particle” by physicist and Nobel laureate Leon Lederman because its existence would bring mass and order to the universe -- a nickname that has been seized on by the media -- it is a term physicists do not particularly care for because of its connotations, said Cumalat.

The existence of the Higgs boson theory is crucial to helping to explain the underpinnings of the universe by confirming the Standard Model of physics that explains why fundamental particles -- the building blocks of the universe -- have mass. Mass is a trait that combines with gravity to give an object weight. Without Higgs boson, there could be no galaxies, stars, planets or people, say researchers.

“It is a very exciting time to be in particle physics and to be involved in an experiment unlocking the meaning of mass,” said CU-Boulder doctoral student Brian Drell.

In addition to Cumalat, Ford and Drell, there are 12 other CU-Boulder people involved in the project: faculty members Uriel Nauenberg, Jim Smith, Kevin Stenson and Steve Wagner; postdoctoral researchers Alessandro Gaz, Eduardo Luiggi, Keith Ulmer, and Shilei Zang; graduate students Bernadette Heyburn, Andrew Johnson and Troy Mulholland; and technical staff members Eric Erdos and Douglas Johnson.

Sixteen years in the making, the $3.8 billion LHC project involves an estimated 10,000 people and staff from 60 countries, including more than 1,700 scientists, engineers, students and technicians from 94 American universities and laboratories supported by the U.S. Department of Energy's Office of Science and the National Science Foundation. The United States is providing about $530 million, primarily for the LHC detectors.

Photo courtesy CERN.