#43
The Wonderful World of Quarks
According to scientists at Australian Swinburne University, the universe is made of many
different materials, but the one most extensively studied is baryonic matter, or regular matter.
One example of baryonic matter is atoms. Baryonic matter, as its name suggests, is made of
baryons (“Baryonic Matter”). According to the Berkeley Lab, baryons are composite subatomic
particles such as neutrons and protons. Electrons, however, are not baryons but leptons. This is
because baryons are composed of three elementary particles called quarks. Leptons, on the other
hand, are not made of quarks, but are elementary particles themselves. There are six different
types, or flavors, of quarks: up, down, strange, charm, top, and bottom. Like electrons, quarks
also have quantum numbers describing their flavors, color and electric charge, and spin.
One can never see the quarks themselves, because of the principle of quark confinement,
which states that particles with color charge cannot be by themselves. Therefore, scientists make
all these observations when quarks are together in groups called hadrons. Baryons themselves are
hadrons. Color charge is a description of how different particles react in strong interactions, one
of the four fundamental interactions of nature. It does not refer to the visual color of a particle,
but instead an analogy to compare the three values of color charge to the three primary colors of
light: red, blue, and green. Quarks’ color charge can be any one of these three colors and change
continuously. Color charge determines the attraction between different quarks, thus allowing
them to form baryons like protons and neutrons. (Particle Adventure). According to Duke
physicist Lena Hansen, when quarks are near each other, they exchange other color charged
particles called gluons, which causes the quarks’ own color charges to change. These gluons are
originally in the space surrounding the quarks, and they are essentially the ones carrying the
color charge, which means that color charge covers a greater amount of space. This makes the
force between them incredibly strong. As quarks move apart, it gets even stronger, which is why
one can never observe these particles separately.
On a composite subatomic particle level, the interaction between the quarks that make up
protons allow them to bind to each other in a nucleus without being repelled, because they have
the same electric charge of +1. This is because each proton’s quark’s color charge causes it to
attach to the quarks of other protons. Since the force of the attraction between different quarks
due to color charge is stronger than the repelling force between the protons holding the same
charge, the protons are attracted to each other. This is called a residual strong interaction
(Hansen).
According to physics educationalist Andrew Zimmerman Jones, a quark’s electric charge
is always a fraction. Charm, top, and up quarks, together called up-type quarks, all have a charge
of +⅔, while the other three quarks, or down-type quarks, all have a charge of -⅓. The sum of a
group of quarks’ charges makes up the electric charge of a hadron, which is always an integer
(Zimmerman Jones). According to Jefferson Lab educator Steve Gagnon, in the example of
baryons, the neutron, made up of two down quarks, each with a charge of a charge of -⅓, and
one up quark, with a charge of +⅔, has a resulting electric charge of 0. This combination of
quarks allows a neutron to be neutral and thus increase the mass of an atom without changing its
properties, creating different isotopes of a single element. The proton, on the other hand, made
up of two up quarks and one down quark, has a consequential electric charge of +1, allowing it to
attract negatively charged electrons and create different elements (Gagnon).
According to Berkeley Labs, the spin of quarks is not like a spin of the conventional
sense. This spin gives these particles nominal periods of time in which it holds magnetic
properties (Particle Adventure). Quarks have a spin of either +½ or - ½ (Zimmerman Jones).
According to scientific journalist Anne Trafton, scientists are unsure what causes spin in protons
themselves, estimating that quarks cause about twenty-five percent of a proton’s spin. (Trafton).
Nevertheless, according to the physics department at Georgia State University, we do know what
that this spin can cause atomic magnetism in single neutrons or protons. However, in a whole
nucleus the answer is more complicated. In a nucleus, the neutrons and protons often form pairs
with the same particle with an opposite spin, making the spin 0. This is how most common
nuclei are, as both the numbers of neutrons and protons are even. However, when the number of
neutrons or protons is odd, a proton or neutron will not have a pair, thus making the spin of the
nucleus the sum of the spin of the unpaired nucleons. This spin gives a nucleus a magnetic
moment, making the atom magnetic (“Nuclear Spin”).
Quarks influence the nucleus of an atom significantly, allowing the protons and neutrons
to stick together due to their color charge, and giving the protons and neutrons their proper
electric charges. However, there is still an abundant amount of information about the properties
of these subatomic particles to discover. Scientists are still unsure why certain particles have
different masses, and they believe that quarks may have shadow particles called squarks, which
would connect the other fundamental forces like strong interactions with the concept of gravity
(Particle Adventure). And, of course, we have yet to find how protons and neutrons themselves
get their spin. Merriam-Webster defines chemistry as “a science that deals with the composition,
structure, and properties of substances and with the transformations that they undergo”
(“chemistry”). Through the study of elementary particles such as quarks, we study the
organization and constitution of all atoms, enabling ourselves to better understand the behavior
of atoms and thus have a better knowledge of chemistry itself.
Works Cited
“Baryonic Matter.” Cosmos. Swinburne University, n.d. Web. 1 Jan. 2013.
“chemistry.” Merriam-Webster.com. Merriam-Webster, 2013. Web. 2 Jan. 2013.
Gagnon, Steve. “Questions and Answers.” Jefferson Lab. Jefferson Science Associates.
Hansen, Lena. “The Color Force.” Duke Physics. Duke University, n.d. Web. 31 Dec. 2012.
“Nuclear Spin.” Georgia State University. Georgia State University, n.d. Web. 2 Jan. 2013.
The Particle Adventure. Lawrence Berkeley National Laboratory, 2012. Web. 31 Dec. 2012.
Trafton, Anne. “How Does the Proton Get Its Spin?.” Phys.Org. Phys.Org, 2010. Web. 2 Jan.
2013.
Zimmerman Jones, Andrew. “Quarks.” About.com. About.com, 2013. Web. 2 Jan. 2013.