What are Quarks? Daniel Moore Materials Science and Engineering Georgia Institute of Technology Friday, March 7, 2014
Overview • Introduction of Quarks • Basic building blocks of nature • Definition • Scale • Discovery of Quarks • Theoretical evidence • Flavors and colors • The difference between protons and neutrons • Summary
Basic Building Blocks of Nature • What is the world made of? • Empedocles first classified the fundamental elements as fire, air, earth, and water. (c. 450 B.C.) • By convention there is color,By convention sweetness,By convention bitterness,But in reality there are atoms and space. -Democritus (c. 400 B.C.) • Is the atom fundamental?
Basic Building Blocks of Nature • The atom is misnamed. The Greek root for the word atom, αυτομον, means "that which cannot be divided." But atoms are made from smaller particles! • The atom contains negatively charged particles, electrons, surrounding a positively charged core, the nucleus. • But even this nucleus isn’t fundamental! It is made up of two types of particles, protons and neutrons.
Basic Building Blocks of Nature • So, are these protons and neutrons fundamental particles? • Physicists have discovered that protons and neutrons are composed of even smaller particles called quarks. • After extensive testing, most physicist believe that quarks are the smallest particles – they are not made of anything else. Nucleus Electrons
Quarks: Definition • “Quarks are a fundamental matter particles that are constituents of neutrons and protons and other matter particles.” • Name comes from James Joyce: “Three quarks for Muster Mark.” Finnegan’s Wake • The names are not important. Enrico Fermi once said to his student, “Young man, if I could remember the names of these particles, I would have been a botanist!” • Quarks are considered part of the “Standard Model” of Physics.
Scale: Size of Quarks • Width of proton = 1 cm centimeter • Width of quarks = less than the diameter of a hair • Width of atom = more than the length of thirty football fields! Proton width Quark width
Discovery: Theory • The proton and neutron were observed to have similar mass. This led people to believe that they were made up of something that was only slightly different. • Murray Gell-Mann proposed (Nobel - 1969) the existence smaller matter particles that had electrical charges that were a fraction of the charge of an electron. • Quarks are never observed individually, so initially they were regarded as mathematical fiction.
Flavors and Colors • A quark’s flavor and color have nothing to do with taste or how it looks. • Six flavors: Up (1968), Down (1968), Strange (1974), Charm (1974), Beauty (1977), Truth (1995) • Three colors: Red, Green, Blue • These types of names are what happen when scientists try to be poets.
P N d u u u d d Difference between Protons and Neutrons • Protons and neutrons consist of three quarks. Proton = up + up + down Charge = 2/3 + 2/3 - 1/3= +1 Neutron = up + down + down Charge = 2/3 - 1/3 - 1/3= 0
Summary • Quarks are a basic building block of nature. • Quarks are 100,000,000 times smaller than an atom. • Quarks come in 6 different flavors and 3 different colors. • Quarks make up a part of the “standard model” of physics.