Quarks are essential to the formation of larger particles. Particles that are composed of 2 quarks are called mesons, and particles that are composed of 3 quarks are called baryons.
Last week we discussed the properties of quarks such as charge and mass. Today we will be discussing quantum spin, quark pair separation and the composition of larger particles.
Spin in quantum physics is different to spin as it is understood in everyday life, it is an expression of angular momentum at the quantum level, where the charges of elementary particles “spin” on their own axes within a given particle. In saying this, I mean that the charge oscillates between positions within the particle. This movement of charge creates a weak magnetic field around the quark. The existence of this magnetic field is the reason why adjacent electrons (which are elementary particles) need to have opposite spin to exist in the same orbital. This is shown by the diagram above, if one electron has a spin that is positive (indicated by the upward arrow) it has to be paired with an electron that has a negative spin (indicated by the downward arrow). Spin can be represented by a vector quantity; the reduced Planck constant. Planck’s constant (h) is the energy of a photon (at rest) divided by the radiation frequency of a photon h=E/v or E=hv, where (E) is energy, (v) is the radiation frequency (or simply velocity) and (h) is Planck’s constant. A simplified version of this constant is the reduced Planck constant (ħ) which equals h/2π. Hence, we can merge the two equations to get energy in terms of the reduced Planck constant (ħ) and the radiation frequency (v) in the form E=2πℏv . By this definition, the spin of fermions can be calculated to be in the form nℏ/2 and the spin of bosons to be nℏ where n is an odd integer and ħ is the reduced Planck constant. Collectively the reduced Plank constant (ħ) is known as the quantum of spin. Thus, we can say that bosons have a full integer spin while the fermions have a half-integer spin. Alongside the different integer spin, fermions are theorized to consist of matter whereas the bosons are considered as force carriers, meaning that the fermions obey the Pauli exclusion principle (which states that no two fermions can have the same quantum spin or state at the same time, e.g. if an electron in the first orbital of an atom has positive ½ spin the electrons in the second orbital will have – ½ spin thus cancelling each other out) and the bosons do not.
Quark Pair Separation
Quarks bond with each other or anti-quarks [next week] through the quantum energy of gluons to make hadrons. It is impossible to find a single quark by itself as they are always bonded to another one by a gluon. The amount of energy required to split the pair is greater than the energy required to create two new quarks as the input energy, therefore before the quark pair has split them there will be enough energy in the system to create 2 new quarks or antiquarks. How can energy be converted to mass, well, this is because the energy put into the system of quarks follows Einstein formula, E = mc2 where the excess energy gets converted into mass by following the Law of Conservation of Mass.
Proton and Neutron Composition
Quarks make up two of the most common hadrons in the universe, neutrons and protons. Protons are made up of millions of quarks and anti-quarks all coming in and out of existence (due to the Heisenberg Uncertainty principle and Einstein’s formula) through the energy that is comprised in the proton. The different quarks can be of any kind given that they are bonded to their corresponding anti-quark that has an opposite charge thus cancelling each other out. For example, an up quark could spontaneously be created but it would have also had to be created with an anti-up quark which has the opposite charge. So how can protons have a charge? And why are neutrons at a neutral charge? This is because alongside the millions of quarks coming in and out of existence, there are also “valence” quarks that are not bound to anti-quarks but rather other matter quarks. This doesn’t mean that they are on the outer layer of the hadron however, this means that they are the quarks responsible for determining the charge of the hadron in question. For example, the proton has a charge of +1, therefore, they are made of 2 valence up quarks (with charges of +2/3 each, which add up to +4/3) and a valence down quark (with a charge of -1/3). When these valences of charges are added up you would get an overall charge of +1, corresponding with the charge of a proton. Similarly, neutrons are made of 2 valence down quarks (with an overall charge of -2/3) and a valence up quark (with a charge of +2/3) thus cancelling out to have an overall charge of 0, as a neutron should have.
Next week we shall discuss my favourite section of particle physics, Anti-matter, as well as the 4 fundamental forces and bosons, so tune in next Monday!!