Matter particles come in two main varieties, leptons and quarks.
VERN BENDER
A polaron is a quasiparticle used in condensed matter physics to understand the interactions between electrons and atoms in a solid material. Polaritons are hybrid particles made up of a photon strongly coupled to an electric dipole. Examples of such a dipole include an electron–hole pair in a semiconductor, which forms an exciton-polariton, and the oscillating electrons at the surface of a metal, which creates a surface-plasmon polariton.
The Standard Model is missing a few puzzle pieces (conspicuously absent are the putative particles that make up dark matter, those that convey the force of gravity, and an explanation for the mass of neutrinos). Still, it provides a highly accurate picture of almost all other observed phenomena. The force-carrying particles (namely the photon, which conveys the electromagnetic force; the W and Z bosons convey the soft power; and the gluons, which give the strong point) are put on the same footing as the matter particles. Those forces act between — quarks, electrons, and their kin. Furthermore, critical properties like “color” are left out.
Matter particles come in two main varieties, leptons and quarks. (Note that there is also an antimatter particle for every kind of matter particle in nature, which has the same mass but is opposite in every other way. As other Standard Model visualizations have done, we elide antimatter, which would form a separate, inverted double simplex.)
Start with quarks, particularly the two types of quarks that make up the protons and neutrons inside atomic nuclei. These are the up quark, which possesses two-thirds of a unit of electric charge, and the down quark, with an electric order of −1/3. Up and down quarks can be either “left-handed” or “right-handed,” depending on whether they are spinning clockwise or counterclockwise concerning their direction of motion.
Left-handed up and down quarks can transform into each other via an interaction called the weak force. This happens when the quarks exchange a particle called a W boson — one of the weak force carriers, with an electric charge of either +1 or −1. There are no right-handed W bosons in nature. This means right-handed up and down quarks cannot emit or absorb W bosons, so they don’t transform into each other. Quarks also possess a kind of charge called color. A quark can have either a red, green, or blue color charge. A quark’s color makes it sensitive to the strong force.
The strong force binds quarks of different colors together into composite particles such as protons and neutrons, which are “colorless,” with no net color charge.
Quarks transform from one color to another by absorbing or emitting gluons, the vital force carriers. These interactions form the sides of a triangle. Because gluons possess color charge themselves, they constantly interact with one another and with quarks: the leptons, the other kind of matter particles. Leptons come in two types: electrons, which have an electric charge of −1, and neutrinos, which are electrically neutral.
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The weak force is a little more complicated than we let on earlier. Aside from the W+ and W– bosons — the electrically charged carriers of the weak force — there is also a neutral carrier of the weak force, called the Z0 boson. Particles can absorb or emit Z0 bosons without changing identities. As with electromagnetic interactions, these “weak neutral interactions” merely cause loss or gain of energy and momentum.
It’s no coincidence that the weak neutral interactions closely resemble the electromagnetic interactions. The weak and electromagnetic forces both descend from a single force that existed in the universe’s first moments, called the electroweak exchange.
As the universe cooled, an event known as electroweak symmetry breaking split the forces in two. This event was marked by the sudden appearance of a field extending throughout space, known as the Higgs field, associated with a particle called the Higgs boson — the final piece of our puzzle.
When the Higgs field arose in the early universe, it joined left- and right-handed particles to each other, imbuing the particles simultaneously with the property we call mass. (Note that the neutrino has mass, but its origin remains mysterious since it derives from some mechanism other than the Higgs.)
As a particle such as an electron moves through space, it constantly interacts with Higgs bosons — the Higgs field’s excitations. When a left-handed electron bumps into a Higgs boson, the electron might ricochet off it in a new direction and become right-handed, then bump into another Higgs and become left-handed again, and so on. These interactions slow down the electron, and that’s what we mean by “mass.”
The more a particle interacts with the Higgs boson, the more mass it has. Furthermore, the frequent interactions with Higgs bosons make those massive particles quantum mixtures of left- and right-handed.
