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.