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A simulation of the two-photon channel shows what ATLAS sees when the decay of a Higgs boson results in the production of two gamma rays. The blue beads indicate intermediate massive particles, and the bright green rods are the gamma-ray tracks. While the two-photon channel is the least likely Higgs decay, it is easier to observe than others with even noisier backgrounds. | Photo courtesy of Lawrence Livermore National Lab
As the United States celebrated its Independence Day, scientists and armchair physicists rejoiced worldwide for a different reason – evidence of the long sought-after Higgs Boson particle.
Researchers at CERN (European Organization for Nuclear Research) in Geneva, Switzerland, the home of the Large Hadron Collider (LHC), announced July 4 at 4:30 a.m. EDT that they discovered a particle that is “consistent with the Higgs boson” particle.
While they didn’t say outright that they “discovered” the elusive particle, the reaction from the science community speaks to the significance of finding a Higgs boson-like particle in the exact place physicists theorized it would be.
Peter Higgs, who theorized the existence of the boson particle in the 1960s, was tearfully elated at the announcement, thinking he'd never see evidence of his theory come to light in his lifetime. Closer to home, in Illinois, 200 Fermilab scientists and other staffers gathered at 2 a.m. in an auditorium to watch the live announcement from Switzerland.
Fermi National Accelerator Laboratory and Brookhaven National Laboratory are the host laboratories for the U.S. contingents of the Large Hadron Collider experiments that found the Higgs boson-like particle. They and researchers from Argonne National Lab, Lawrence Berkeley National Lab and SLAC National Accelerator Lab are among the 1,700 scientists, engineers, technicians and graduate students from the United States that helped design, build and operate the LHC accelerator and particle detectors, and analyze the data from the collisions.
So, what exactly is the Higgs boson? Higgs and other physicists theorized that empty space is not empty. They weren’t just talking about the empty space between, let's say, the planets or solar systems, but the empty space between subatomic particles. Instead, they said this space was a medium called the Higgs field, which is continuous, has no holes, and consists of many individual particles called bosons.
Fermilab physicist Don Lincoln compares the Higgs field to water. In this analogy, the water plays the role of the field. The individual water molecules (H20) are the Higgs bosons that make up the field.
A barracuda, he says, is a narrow fish that interacts only slightly with the water around it, so it can move very quickly. The barracuda would represent a very light subatomic particle, like an electron, or one of the massless particles that we’re trying to catch at the IceCube Neutrino Observatory in Antarctica.
A less aerodynamic animal, like a person swimming, doesn't move as quickly, in part, because of their drag in the water. The person would represent a very large subatomic particle.
For particles that travel through the Higgs field (ie - all of them), the buildup of Higgs bosons in their path creates push back, or resistance, which explains the existence of mass. (Large particles encounter more resistance in the field, so they have more mass. Some particles encounter no resistance, thus are considered to be massless.)
So, why is this discovery so important? Mass is a fact. People have mass. Particles have mass. Though, before this we couldn’t necessarily say why. The Higgs boson is the final piece of the puzzle for a few items in the Standard Model.
In the 1960s, physicists came up with the Standard Model, which theorized the existence of the smallest particles in the universe, like quarks and leptons, and also new forces and fields that keep all the new particles together.
Starting in the 1970s, physicists went straight down the list discovering all of the new subatomic particles theorized in the Standard Model, except one – the Higgs boson.
Going into this most recent run of the Large Hadron Collider, researchers had a pretty good idea of what the Higgs boson looked like, in theory. Last August, researchers excluded the existence of the Higgs boson in the mass region 145 to 466 GeV, the higher end of the mass range they suspected, and announced they suspected the particle to have a mass of 116 to 130 GeV.
They announced yesterday that the particle has a mass of 125 or so GeV with its predicted properties.
Finding Higgs boson-like particle may close the book on the Standard Model, and in doing so opens many other doors for discoveries in the areas of particle and theoretical physics.