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A Prerequisite: What are Quarks ?  What’s a Boson ?

Quarks are subatomic particles, first proposed in 1964 by Gell-Mann and Zweig.  They are believed to be among the fundamental constituents of matter interacting via the strong force to make up protons and neutrons.  There are six types,
or flavors, of quarks that differ from one another in mass and charge and are grouped in three pairs: up and down, charm and strange, and top and bottom.  Quarks appear to be true elementary particles such that they have no apparent structure and cannot be resolved into something smaller.  Evidence for their existence was first discovered from experiments by the Stanford Linear Accelerator in 1968.  Experiments verified all six flavors of quarks, the last to be discovered was the top quark by Fermilab in 1995. 

Quarks always seem to occur in combination with other quarks called antiquarks, or antiparticles, to form all hadrons which are the so-called strong interacting particles encompassing both baryons and mesons.

Quarks have fractional electric charge values, either 1/3 or 2/3 times the elementary charge, depending on flavor.  Up, charm,
and top quarks have a charge of +2/3, while down, strange, and bottom quarks have −1/3.  Antiquarks have the opposite charge to their corresponding quarks; up-type antiquarks have charges of −2/3 and down-type antiquarks have charges of +1/3.  The hadron’s electric charge is the sum of the charges of the constituent quarks and have integer charges: the combination of three quarks (baryons), three antiquarks (antibaryons), or a quark and an antiquark (mesons) always results in integer charges.

Spin is an intrinsic property of elementary particles and are often visualized to spin about an axis, although at the subatomic scale particles are considered point-like and therefore given a spin vector.

From Quantum Mechanics, quarks are classified as fermions and are considered spin-1/2 particles.  This differs from bosons which have integral spins.  An important characteristic of bosons is that their statistics do not restrict the number that can occupy the same quantum state.  On the other hand, quarks are subject to the Pauli exclusion principle, which states that no
two identical fermions can simultaneously occupy the same quantum state.   

While most bosons are composite particles, in the Standard Model, there are five bosons which are elementary: the four gauge bosons, and the Higgs boson.  The Higgs boson particle was theorized in 1964 and discovered at CERN in 2012.  Its existence is considered pivotal to the Standard Model, and other theories within particle physics.  The unanswered question of the Higgs Boson in fundamental physics was of such importance that it was searched for more than 40 years and finally led to the construction of one of the world's most expensive and complex experimental facilities to date, the Large Hadron Collider. 

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