Particles 101
It is known that everything in the known plane of existence is made of atoms. One atom usually consists of a set of protons (particles with positive charge), neutrons (particles with neutral charge) and electrons (particles with negative charge). The general scale of the atom is a ten billionth of a metre. The actual atom in question has a central nucleus, which is made of protons and neutrons. A force called the ‘Residuum Strong Force’ holds it together. This article will cover what is inside the protons and neutrons and will discuss particles, spins and charges.
Particles
Particles are small units of matter. Elementary particles are particles that (as far as we know) cannot be broken down any further. Electrons are elementary particles, but protons and neutrons are not; within a proton and a neutron are more particles called quarks.
Elementary particles are like Lego blocks; they can be used to make bigger blocks, which can be used to make bigger blocks. All Elementary particles are split into two groups, bosons and fermions, the allocation to which is defined by the spin of the particles. The spin of a particle does not actually mean that the particle spins on an axis – in fact, particles do not spin on their axes. The word “spin” is just another way of referring to the scale of the magnetic field produced by the particles. Any particles with fractional spins (e.g. ½, 1 ½, 2 ½) are fermions and any particles with integer spins (e.g. 0, 1, 2) are bosons. The group of fermion particles can be further split into two subgroups: quarks and leptons. What separates quarks and leptons are their charges,the charge of a particle being the property of a particle that determines whether it will attract or repulse other particles. Quarks are the only known group of particles known to have fractional charges (e.g. +23, –13) whereas leptons have full integer charges (e.g. +1, -1). Meanwhile, bosons do not have subgroups and have their own list of particles.
As a reference, the list of quarks includes: up, down, charm, strange, top and bottom. Note that the six quarks can be put into pairs as follows: up and down, top and bottom, charm and strange. These pairs have corresponding charges, for example, up has a charge of +2/3 and down a charge of -1/3. All particles in the quark subgroup have respective antiparticles like up antiquark or down antiquark, which have opposite charges. An example of an antiparticle charge would be up and up antiquark where up has a charge of +2/3 and up antiquark has a charge of -2/3.
The list of leptons includes: electron, electron neutrino, muon, muon neutrino, tau and tau neutrino. All the neutrino particles (tau neutrino, electron neutrino and muon neutrino) have a neutral charge of 0 and the other particles (tau, electron and muon) have a negative charge of -1. Leptons also have their respective antiparticles (antileptons). The antileptons of the neutrino particles are similar to their positive counterpart save that their beta decay behaves differently. Beta decay is when particles become other particles to strengthen the bond between them. Beta decay only happens within the nucleus of an atom.
The list of Bosons goes as follows: Photon, W boson, Z boson, Higgs boson, gluon and graviton. What also makes bosons special, besides the integer spin, is the fact that all boson particles are their own antiparticles except W boson. The reason for this is that the W boson has a negative charge of -1 whereas all the other bosons have the neutral charge of 0. One other feature concerning bosons is that unlike quarks and leptons, these particles are affected by only one of four of the fundamental forces of nature. The four forces are gravitation, weak interaction, electromagnetism and strong interaction. These forces affect the particles except that the bosons are affected by only one of the four. The gluons are affected by strong interaction, the W and Z bosons are affected by weak interaction, the higgs boson is affected by mass and the graviton is affected by gravity.
Composite Particles
Composite particles are particles that are made up of other particles. The proton is a composite particle as it is made of two ups and a down quark. A hadron is a composite particle and can be split into a number of groups. Baryons and mesons are two popular types of hadrons, where mesons consist of 3 quarks or 3 antiquarks and baryons consist of 1 quark and 1 antiquark. There are a number of other hadrons however, like glueballs, hybrids, tetraquarks and the newly discovered pentaquark. A proton is an example of a meson as it has 2 up quarks and a down quark. The nucleus of an atom could also be considered a composite particle, as it is a particle that is made of other particles. The atom is a composite particle. Molecules, which are multiple atoms mixed together are also composite particles.
Atomic Nucleus
As seen in the first figure, the protons and neutrons are stuck to each other in the nucleus or centre of the atom. A force known as residual strong force holds them together. As seen in the second figure, within a proton are three quarks with a connection. In the theory of quantum chromodynamics, quarks and gluons within hadrons have three ‘colours’ (blue, green and red) and three ‘anticolours’ (antiblue (yellow), antired (turquoise) and antigreen (pink)). Each quark in the proton is its own respective colour. The quarks exchange gluons, which in turn change the colour of the receiving quark. For example, a blue hadron could exchange a blue gluon, which makes the receiving green hadron blue, and vice versa (see figure 5). The exchange of gluons creates a force, which holds the quarks together. This strong chromodynamics force does decay a little over time; this decay then holds the actual proton and other neutrons together. This is the reason why this force is known as residual strong force.
Charge and Spin
All particles are defined by a set of properties; these include affecting forces, mass, spin and charge to name a few. Of all the properties, charge and spin are the most varying within particles.
Most particles (save neutrinos and bosons, with the exception of the W boson) are ‘charged’, meaning they either attract or repel each other. Positive particles repel each other but opposite charges attract. It is the intensity of this attraction that determines the measurement of the charge, i.e. stronger opposite charges heavily attract each other. The charges are measured in coulombs, which are usually denoted as e. If the measurement is negative (e.g. -2/3), then the charge is negative and will be attracted to positive measurements.
Spin is the property of a particle that causes magnetic fields. The word spin is merely a term for the unit of measurement to determine the size of the magnetic field. As said before, the particle is not actually spinning on an axis. The origin of the word came from the 70’s when certain electrons were observed to have had magnetic fields; this was not possible considering the way electrons moved. It was hypothesized that electrons spin on an axis, but after further examination, it was concluded that electrons do not spin on an axis. Therefore, in the current state of modern physics, it is unknown still what causes these magnetic fields.