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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
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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.