Search for Higgs Boson at LHC Reveals New Particle

Two Large Hadron Collider (LHC) experiments presented preliminary results Wednesday that describe a new particle consistent with the long-sought Higgs boson, the famous missing ingredient in the Standard Model of particle physics. The findings could help unlock some of the universe’s deepest secrets.

“We have reached a milestone in our understanding of nature,” said Rolf Heuer, director general of CERN (European Organization for Nuclear Research). “The discovery of a particle consistent with the Higgs boson opens the way to more detailed studies, requiring larger statistics, which will pin down the new particle’s properties and is likely to shed light on other mysteries of our universe.”

The Standard Model of physics describes the fundamental particles from which we, and every visible thing in the universe, are made, and the forces acting between them. All the matter that we can see, however, appears to be no more than about 4 percent of the total. A more exotic version of what has been dubbed the “God particle” could be a bridge to understanding the 96 percent of the universe that remains obscure.

Event recorded with the CMS detector in 2012 at a proton-proton center of mass energy of 8 TeV. The event shows characteristics expected from the decay of the SM Higgs boson to a pair of photons (dashed yellow lines and green towers). The event could also be the result of known Standard Model background processes. (Images: CERN)

Scientists first proposed the existence of the Higgs boson — whose coupling with other particles would determine their mass — in 1964. Experiments at CERN’s LEP collider and at the Tevatron collider at the US Department of Energy’s (DoE) Fermilab have searched for the Higgs boson, but it has eluded discovery.

Only now, after decades of developments in accelerator and detector technology and computing — not to mention advancements in the understanding of the rest of the Standard Model — are scientists approaching the moment of knowing whether the Higgs was the right solution to this problem.

“What we are observing is very likely a new particle with very large mass that would have to be a boson,” said University of California, Santa Barbara, physicist Joe Incandela, a spokesman forthe CMS experiment. “This is potentially a historic and very profound step forward in our understanding of the underlying structure of our universe.”

The ATLAS (A Toroidal LHC ApparatuS) and CMS (compact muon solenoid) experiments at CERN released preliminary results of a new particle in the mass region around 125-126 GeV. Publication of the analyses, based on data collected from 2011 and 2012, is expected around the end of the month. A more complete picture of the observations will emerge later in the year after the LHC provides the experiments with more data.

In December, the CMS and ATLAS experiments announced seeing hints of a new particle in their hunt for the Higgs. Since they resumed gathering information in March 2012, both experiments have more than doubled their collected data. Statistical significance of earlier hints at finding the God particle has grown.

Real CMS proton-proton collision events at the Large Hadron Collider in which four high-energy electrons (red towers) are observed. The event shows characteristics expected from the decay of a Higgs boson but is also consistent with background Standard Model physics processes.

“The results are preliminary, but the 5 sigma signal at around 125 GeV we’re seeing is dramatic,” Incandela said. “This is indeed a new particle. We know it must be a boson, and it’s the heaviest boson ever found. The implications are very significant, and it is precisely for this reason that we must be extremely diligent in all of our studies and cross-checks.”

When protons collide in the LHC, their energy is converted into mass and often creates short-lived particles. These particles quickly decay into pairs of lighter, more stable particles that scientists can record with detectors.

Theoretical physicists have predicted the rate at which the Higgs boson will be produced in high-energy proton-proton collisions at the LHC and also how it decays into certain combinations of observable particles. Experimental physicists at the ATLAS and CMS experiments have been studying these collisions, discovering the new particle. They will need to collect more data and run further analysis to determine its properties.

“If the new particle is determined to be the Higgs, attention will turn to a new set of important questions,” said University of California, Irvine, physicist Andy Lankford, deputy spokesman of ATLAS. “Is this a Standard Model Higgs, or is it a variant that indicates new physics and other new particles?”

More than 1700 scientists and graduate students from US institutions — including 89 American universities and seven DoE national laboratories — helped design, build and operate the LHC accelerator and its four particle detectors. The US, through the DoE’s Office of Science and the National Science Foundation, provides support for research and detector operations at the LHC and also supplies computing for the ATLAS and CMS experiments.

For more information, visit: www.cern.ch