Subatomic Particles

What are the smallest particles we know about?
Answered by Science Channel
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  1. For many years, the only known subatomic particles were protons, neutrons and electrons. By the 1960s, however, advancements in particle accelerator technology had shown evidence of hundreds of smaller constituent particles. By studying these particles -- all part of what is known in particle physics theory as the standard model -- physicists can try to explain all of the forces and matter existing in the universe.

    These smallest particles fall into several main categories, most notably fermions, hadrons and bosons. Fermions are the building-block particles. There are two types of material fermions: quarks, which work to hold the nucleus of an atom together, and leptons, which do not. Fermions can be broken down even further: There are different types of quarks, and for each, an antiquark. Quarks are found in groupings, but leptons are found alone. Electrons and neutrinos are examples of leptons. Fermions have a half-integer spin [source: University of California Davis].

    Hadrons are composite particles made of smaller particles. A proton, for example, is a hadron made from a combination of different quarks. Strong interactions bind the hadrons together and they always have charges, but no color. Protons and neutrons are the most stable hadrons. Hadrons come in two classes: baryons and mesons. Hadrons perhaps get more attention in the news that their other super-small relatives because of work being done on the Large Hadron Collider at the European Laboratory for Particle Physics, or CERN, outside Geneva, Switzerland. The collider is a huge particle buster, smashing particles into each other in several combinations in an attempt to find the elusive Higgs boson [source: Pachal].

    Bosons are subatomic particles that carry force. They help particles interact with one another without touching, much like the forces of gravity or magnets. Unlike fermions, bosons have integer spin. The Higgs boson is believed to be the tiny particle that likely provides mass to all matter. Yet scientists aren't even sure that the Higgs boson exists, so researchers at the CERN collider and a few others, including the Fermilab in Illinois, are hunting for it [source: Wall]. The Higgs boson remains one of the key questions remaining in physics and in wrapping up the Big Bang theory. If scientists can identify and study the particle that gives mass to all others, they can explain how the universe started from a seemingly invisible field.

    The search for the Higgs boson is so popular that there is now a smartphone app just for following atom-smashing activities at the Large Hadron Collider [source: Pachal].

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