Particle Physics for Dummies
Many people have a basic understanding of physics: we can recite Newton’s Laws of Motion and know that atoms make up everything and atoms are made of protons, neutrons and electrons. However, most people don’t know that atoms are made up of more than just protons, neutrons, and electrons. To define an atom better, we need to dive into the world of particle physics and take a look at the Standard Model; a theory that explains the hundreds of particles and complex interactions between them.
The standard model states that the universe is made of three different types fundamental building blocks: quarks, leptons and force carrier particles. These particles are simple and structureless and are not made of anything smaller. The model also states that there are four fundamental interactions that all forces in the world can be attributed to. These forces are gravity, strong force, weak force and electromagnetic force. For every particle, there is also a corresponding anti-particle. Anti-particles are essentially the same as their corresponding particles, except they have an opposite charge.
According to the Standard Model, quarks are the particles that make up protons and neutrons. There are six quarks, all grouped in pairs. Listed from lightest to heaviest they are: up/down quarks, charm/strange quarks, and top/bottom quarks. Unlike larger particles, quarks have a fractional charge- up, charge and top quarks have a ⅔ charge and down, strange and bottom quarks have a -⅓ charge. Due to their fractional charge, quarks only exist in groups with other quarks. These groups are known as hadrons.
Hadrons have a net integer electric charge. There are two types of hadrons- mesons and baryons. Mesons are the simpler of the two types since they only consist of 1 quark and 1 antiquark. Anti-particles of mesons just have the quark and antiparticle switched. An example of a meson is a pion which is made of an up quark and a down antiquark. Anti-pions are made of down quarks and up antiquarks. Baryons on the other hand are a bit more complicated, since they are made of any three quarks. Common baryons are protons (two up quarks and a down quark) and neutrons (a up quark and down quark).
There are also six leptons in the Standard Model: electrons, muons, tau and electron neutrinos, tau neutrinos, and Muon neutrinos. The three neutrinos have no charge and are very little mass so they are hard to detect and are only produced in particle decays. Electrons, muons and tau leptons are not found in ordinary matter because they decay very quickly after they are produced. These heavy leptons decay into lighter leptons and always decay into the corresponding neutrino. Leptons are divided into three families, the electron and its neutrino, the muon and its neutrino, and tau and its neutrino.
In the Standard Model, all four fundamental interactions have force carrier particles attributed to them. See, in the Standard Model, forces aren’t just things that act on particles. Instead, forces pass between particles through force carrier particles. Electromagnetic force is the force most people are familiar with, as it is commonly referred to as magnetism. Electromagnetism’s force carrier particle is the photon and its effect is always seen due to the fact that electromagnetic forces between the charged parts of atoms cause atoms to form molecules and much larger objects. Although electromagnetism is the force that most people are familiar with, the most important force is Strong force. Strong force is referred to as such because it is so strong, it offsets electromagnetic force and manages to hold the nucleus together. Its force carrier particles are gluons which bind quarks together by creating very strong force fields when quarks exchange gluons. W+ , W -and Z particles are the force carrier particles for the weak force- a force responsible for the decay of the heavier leptons (Electron, Tau and Muon) and the heavier quarks into lighter ones. Lastly, gravity- the force that holds you on earth- has the graviton for its force carrier particle.
Particle physics is a lot to take in in one sitting, but hopefully you get the gist of things now. Most moderns physics experiments done today are based on proving/disproving parts of the Standard Model. So, now that you understand the basics, the next time a major scientific study is published on particle physics, you will be able to apply your newfound knowledge!