December 13, 2011 — An international team of scientists today announced that experiments conducted during the past two years at the Large Hadron Collider in Europe may be seeing a hint of the Higgs particle (sometimes called "the God particle"), which is believed to give mass to every other particle in existence and may be the underlying basis of matter.
Theorists have predicted that subatomic particles gain mass by interacting with other particles called Higgs bosons. This particle, sought for more than 50 years, would explain the origin of mass. The Higgs boson is the only undiscovered part of the standard model of physics, which describes the basic building blocks of matter and their interactions.
"This is a very exciting time for those of us working at the LHC," said Brad Cox, a professor of physics in the University of Virginia's College of Arts & Sciences and principal investigator for U.Va.'s Compact Muon Solenoid Detector experiment at the Large Hadron Collider. "We are perhaps seeing the first evidence for the Higgs particle. However, we do not want to get ahead of ourselves. Statistically, what we are seeing could be a fluctuation of backgrounds, meaning there is still considerable uncertainty if what is observed is really the Higgs particle. However, what we see so far is exciting. By this time next year we should have conclusive evidence, pro or con, about the structure that we are seeing."
Cox and a team of U.Va. researchers have been planning experiments for the collider and constructing particle detectors for several years.
Experiments began in earnest at the facility, located on the Swiss/French border, in November 2009 after a decade-and-a-half of preparation and construction, and will go on for decades. The experiments are designed to bring new understanding about the basic structure of matter and insight into how the universe began and evolved.
Researchers at the collider are circulating opposing high-energy beams of protons at nearly the speed of light around a 17-mile circular accelerator, producing extreme high-energy collisions that shatter those protons and produce new particles, including, possibly, the Higgs. Experiments replicate the conditions of the infant universe, the time before particles formed into atoms and molecules, and before elements coalesced to make the stars and planets.
"If what we are beginning to see is truly the Higgs particle, it will be a tremendous discovery and accomplishment," Cox said. "The U.Va. group is proud to be a very active participant in its discovery. We hope that this will be only the first of many discoveries as we go on to high energies and intensities at the LHC."
Using a huge international computer grid, U.Va. physicists and colleagues at dozens of institutions worldwide are now sorting through reams of data from the CMS experiment's 100 million channels of electronics.
Cox, with U.Va. colleagues Robert Hirosky, Christopher Neu, Sergio Conetti, Alexander Ledovskoy, Michael Arenton and Sarah Boutle, plus grad students Michael Balazs, Rachel Yohay, David Phillips, Brian Francis, Chuanzhe Lin, John Wood and Joey Goodell, have helped develop and test components for the Compact Muon Solenoid electromagnetic detector, part of the $400 million Compact Muon Solenoid detector most critical in the Higgs hunt.
Higgs bosons, if they exist, are short-lived and can decay in many different ways. Just as a vending machine might return the same amount of change using different combinations of coins, the Higgs can decay into different combinations of particles. Discovery relies on observing statistically significant excesses of the particles into which they decay rather than observing the Higgs itself. The Higgs decay into two photons, which are detected by the CMS electromagnetic detector, is the most important mode of decay for the standard-model Higgs observation.
Over the coming months, physicists will focus on refining their analyses and will begin taking new data in spring 2012, continuing until spring of 2013.
If scientists find subtle departures from the standard model in the Higgs’ behavior, this would point to the presence of new physics, linked to theories that go beyond the standard model. Observing a non-standard model Higgs would immediately open the door to new physics.