The particles that we know today was created during the early stages of the big bang. The particles are grouped according to how they are affected by the four fundamental forces of nature. All of
their masses are influenced by gravity. The electromagnetic force acts on any particles with a charge. The weak and strong nuclear forces act on the nucleus within an atom. Hadrons interact with
all forces while leptons are unaffected by the strong force.
The standard model
The word ‘atom’ means indivisible. Discoveries during the early 20th century prove that the atom is indeed divisible. The first standard model of the atom consisted of electron, protons and
neutrons.
The particle zoo
The fundamental forces in Nature
To understand the nature of the elementary particles , you would first have to understand the forces between them. All of the particles are subject to the four fundamental forces: Gravity,
electromagnetic, weak and strong nuclear.
The strong force is very short ranged and binds the protons and the neutrons together.
The electromagnetic force is not as strong as the strong force and is responsible for binding atoms and molecules together. It is a long force that decreases in strength as the inverse square of
the separation.
The weak force is a short-range nuclear force that tends to produce instability in certain nuclei. It is responsible for radioactive decay.
The gravitational force is a long-range force that has the weakest relative strength.
The interactions between the particles are often described in terms of the exchange of quanta (refers to energy ‘how much’).
Antiparticles
Most particles have antimatter counterparts. It is believed that an equal amount of matter and antimatter were created in the early universe. When a particle meets it’s antimatter particle, they
annihilate each other and create a burst of radiation (which could be cause of the early universe being full of radiation).
Classification of particles
All particles other than mediating field particles of the fundamental forces can be classied into two broad categories, Hadrons and Leptons.
Hadrons
Particles that interact through the strong force are called hadrons. There are two classification of hadrons, mesons and baryons. These are classified according to their masses and spins.
Mesons : They all have zero or an integral spin (0 or 1). All mesons decay into electrons, positrons, neutrinos and photons. The pion is the lightest known meson.
Baryons: A second class of hadrons, have a mass that is greater or equal to that of a proton. Their spin is always a non- integer value (1/2 or 3/2). Protons are neutrons are included in the
baryon family. All baryons decay in such a way that the products always include a proton.
The hadrons are composed of more units called quarks.
Quarks
Leptons may be truly elementary particles because they have no measurable size(…) or internal structure. Hadrons are complex having both size and structure.
Hadrons are composed of two or three fundamental constituents called ‘quarks’ (the name taken from the passage ‘Three quarks for Muster Mark’). The most unusual property of a quark is that it has
unusual charges. The up-type quarks have a charge of 2/3e and the down-type quarks -1/3e.
Mesons consist of one quark and an antiquark while baryons consist of three quarks.
Quarks had compositions that violated the Pauli exclusion principle. A new property of quarks was established called colour .
Leptons
It means small or light. It refers to a group of particles that participate in the weak interaction. All leptons have a spin of 1/3.
Included in this group are electrons, muons and neutrinos (Which are all very light). The number of leptons are quite limited and it is believed that there are only six leptons.
Although Neutrinos appear to be massless, there is a small chance that they have a small, non-zero mass.
( A fun quiz: Which particle are you?)
