Along with dozens of other outlets, we recently reported on the results of a new study that may show that the Standard Model of Particle Physics is irretrievably broken. On the other hand, other studies have shown that it may not be broken at all.
Why this was such a big deal is that the Standard Model accounts for all 17 of the elementary particles and the four fundamental forces that make up our universe. Elementary particles are particles that are not comprised of other particles.
The Standard Model first began taking shape in 1897, when the English physicist J.J. Thomson discovered the electron, and it wasn't considered complete until 2012, with the discovery of the Higgs boson.
As the chart above shows, our universe is comprised of six quarks and six leptons. These are the particles that make up atoms — quarks within protons and neutrons, and electrons surrounding the nuclei.
Four fundamental forces are at work in our universe: electromagnetism, the strong force, the weak force, and gravity. Unfortunately, the Standard Model cannot account for gravity, so for now, we're going to ignore it. The remaining three forces result from the exchange of "force-carrier" particles, or gauge bosons. Particles transfer discrete amounts of energy by exchanging bosons with each other. Each fundamental force has its own corresponding boson.
The Electromagnetic Force is transmitted between electrically charged particles by the photon, which is massless. The Weak Force is transmitted between quarks and leptons by the W+, W−, and Z gauge bosons, which are massive particles, with the Z boson being more massive than the W±.
The Strong Force is transmitted between quarks by eight gluons, which are massless. Quarks and gluons are "color-charged". Color-charged particles exchange gluons in strong interactions. Two quarks can exchange gluons and create a very strong color field that binds the quarks together. Quarks constantly change their color charges as they exchange gluons with other quarks. Because gluons themselves have color charge, they can interact with one another.
Standing by itself on the far right side of the Standard Model chart, like a king or queen, is the Higgs boson. It may not be farfetched to call it royal since the famed physicist Leon Lederman had dubbed it "The God Particle". Lederman coined that phrase for the title of his 1993 book, The God Particle: If the Universe Is the Answer, What Is the Question?
The Higgs boson
Back in 1964, English physicist Peter Higgs submitted a paper to a scientific journal that contended that all of space is filled with a field, which came to be called the Higgs field, that imparts mass to objects. Scientifically, mass is defined as the resistance offered by a body of matter to a change in speed or position on the application of force.
You can think of the Higgs field this way: Push a ping-pong ball through the air and it moves almost without resistance, but push that same ping-pong ball through water, and it will be much harder to push. The Higgs field is like the water.
When the scientific journal initially rejected Higgs' paper, he revised it with the significant addition that his theory predicted the existence of a heavy boson
In the 1970s, physicists realised that there are very close ties between the weak force and the electromagnetic force. They developed the basic equations of a unified theory which propsed that that electricity, magnetism, light, and some types of radioactivity are all manifestations of a single force known as the electroweak force. This force is carried by the photon, and the W and Z bosons.
But there was a problem. The equations predict that these particles have no mass, and physicists already knew that the W and Z bosons have mass. Fortunately, theorists Robert Brout, François Englert and Peter Higgs made a proposal to solve this problem. They proposed that the W and Z bosons interact with a force called the "Higgs field". The more a particle interacts with this field, the more mass it has.
Gradually, other physicists came to realize that Higgs' idea fit perfectly with the equations of the Standard Model. The only problem was that there was no experimental evidence to back up the theory. If the Higgs field existed, it should have a gauge boson, called the Higgs boson, and physicists' calculations showed that the Higgs boson should be very massive, and that it should decay almost immediately.
How to do you induce such a massive and emphemeral particle to appear? It would take over 30 years before particle colliders, detectors, and computers capable of looking for Higgs bosons were created. Enter the Large Hadron Collider.
The Large Hadron Collider, which opened in September 2008, is located at CERN, or the European Council for Nuclear Research. It is a 17-mile-long (27.35 km) ring that runs primarily beneath Geneva, Switzerland, and it uses around 9,000 superconducting magnets to corral millions of protons which are circling the ring, in both directions, at close to the speed of light.
At specific points along the ring, the two proton beams collide and produce sprays of particles which are observed by enormous detectors. On July 4, 2012 physicists around the world gathered in meeting rooms to hear and see a press conference being given at CERN. The purpose of the press conference was to announce the discovery of the Higgs boson and in the audience was 83-year-old Peter Higgs. Video of Higgs taking out his handkerchief and wiping his eyes went viral.
In 2013, a year after the discovery of the Higgs boson, Peter Higgs, along with François Englert, was at last honored with a Nobel Prize in Physics. On the day of the Nobel announcement, Higgs, who doesn't own a cell phone, went to the store and it was only when he bumped into one of his neighbors that he found out that he had won the prize.
The Higgs field
The Higgs field differs from other fields, such as electromagnetic or gravitational fields, in that it is unchanging. An electromagnetic field waxes and wanes depending on how close you are to it. The strength of a gravitational field is also determined by where you are — stand next to a black hole and you'll experience a much stronger gravitational field than you would standing on Earth.
By contrast, the Higgs field appears to be the same no matter where you are in the universe, and it appears to be a fundamental component of the fabric of space-time. The property of "mass" is a manifestation of potential energy transferred to elementary particles when they interact with the Higgs field, which contains that mass in the form of energy.
Spin is the intrinsic angular momentum of an elementary particle. In quantum field theory, the spin of a particle is related to its behavior. For example, bosons have an integer spin (0, 1, 2, etc), and so can occupy the same quantum state at the same time. In contrast, particles with half-integer spin (1/2, 3/2, etc) cannot. In the Standard Model, the components of matter (electron, quarks, etc.) are spin 1/2 particles, while the particles which transmit force (photon, W/Z, gluon) are spin 1 particles.
The Higgs field is the only scalar, or spin 0, field. The Higgs field imparts large masses to the W and Z gauge bosons. Their masses affect how far the W and Z bosons can travel, thus confirming the weak force's extremely short range.
The Higgs boson is a massive scalar boson, having zero spin, no electric charge, and no color charge. As predicted, it has a hefty mass of 125 GeV, and a mean lifetime of 1.56×10−22 seconds. The Higgs boson has been observed decaying into a pair of bottom-antibottom quarks, two W bosons, a tau-antitau pair, two Z bosons, and two photons. It is also predicted to decay into two gluons, a muon-antimuon pair, and possibly others particles.
While the Higgs field generates the masses of the leptons — the electron, muon, and tau — and the masses of the quarks, it does not generate mass for the photon and the gluon. And, because the Higgs boson is itself massive, that means that it must interact with the Higgs field.
The future of the Higgs field
Currently, scientists are trying to determine if the Higgs field gives mass to the three "flavors" of neutrinos — electron neutrinos, muon neutrinos, and tau neutrinos. It was long believed that neutrinos were massless, however, it is now known that each neutrino has its own distinct mass.
In addition, physicists now believe that 95 percent of our universe is not made of ordinary matter, but consists of dark energy and dark matter. Scientists at CERN are trying to determine if dark energy and dark matter interact with the Higgs field. According to CERN, dark matter has mass, and physicists have suggested that dark-matter particles could interact with the Higgs boson, with a Higgs boson decaying into dark-matter particles.
Going forward, the Higgs boson will be an invaluable tool for searching for signs of physics beyond the Standard Model of Particle Physics.