THE STANDARD MODEL

The standard model of particle physics is a devised array of known fundamental particles along with their properties like mass, spin, and charge. It is the set of seventeen particles (till date) that explains the making of the universe and enlightens us to the interactions between its elements. The model comes to us by way of particle physics, a field filled with physicists dedicated to reducing our complicated universe to its most basic building blocks. The standard model majorly constitutes fermions and bosons.

atom

Fermions are the building blocks of matter. There are twelve known fermions. The fermions are further divided into quarks and leptons. The spin possessed by the fermions is ½.

Bosons are the mediators of interaction between matter. There are five known bosons. The bosons are subdivided into gauge bosons and scalar bosons. The spin possessed by gauge bosons is 1 whereas scalar bosons are 0-spin particles.

A spin, as defined in quantum physics, is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei.

standard model

*Refer to the standard model table

QUARKS

There are six quarks sub-divided into three generations. The first generation constitutes the up quark and the down quark, the second generation constitute the charm quark and the strange quark, and the third generation constitutes a top quark and a bottom quark. All these six quarks are joined together in a varying fashion to give out different particles. Example, two up quarks, and one down-quark make a proton and one up-quark, and two down-quarks make a neutron.

EDIT 1

Earlier it was believed that protons and neutrons are the fundamental particles, but it was discovered, only after the particle accelerator was invented and employed to crash two hadrons (protons and neutrons) at light speeds that protons and neutrons are made up of quarks held together by strong nuclear forces carried by gluons. The remaining four quarks combine with each other as well as with leptons to form massive forms of matter. These quarks are way more heavier than the up and down quark. (The top quark decays into Higgs boson (God particle), or bottom quark).

LEPTONS

There are six leptons in all sub-divided into three generations. The first generation constitutes the electron and electron neutrino, the second generation constitute the muon and muon neutrino and the third generation constitute tau and tau neutrino. Neutrinos are tiny, nearly massless particles that travel at, near light speeds. They have zero a charge. They were first discovered in 1956. Leptons are the fundamental particles that combine with other composites to form some complex matter (like positronium). (electrons, unlike protons and neutrons are subatomic particles which are fundamental in quantum mechanics)

BOSONS (FUNDAMENTAL FORCE CARRIERS)

Before we get to know another class of fundamental particles (bosons) we must gather knowledge of the force fields that carry them. There are four known fundamental forces:

snf

Strong Nuclear force: The strong nuclear force holds quarks together to form protons & neutrons and ultimately confines the two, together in a nucleus (strong nuclear force is way more stronger than the electromagnetic force that repels protons).

SM%

Weak Nuclear force: The weak nuclear force causes transformation of protons to neutrons and vice-versa, along with other radioactive phenomena. The fusion and fission processes are examples of weak nuclear forces.

emf

Electromagnetic force: Electromagnetic (EM) radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays, gamma rays, etc… The force of electromagnetic attraction or repulsion between electric charges is inversely proportional to the square of the distance between them. The electromagnetic force is carried by photons which are massless.

Gravitational force: Gravity is the field created by a mass distribution in the space-time around it; gravitational force is the force exerted by the field on a test mass in the field.

gf
The difference is that the gravitational field is there in absence of a test mass, but the gravitational force exists only if there is a test mass within the field. From Einstein’s general relativity, gravity is the space-time curvature induced by an energy-mass distribution.

GAUGE BOSONS

Gluon is the strong nuclear force carrier which helps in the formation of protons, neutrons and ultimately the nucleus. These particles possess the highest strength, but their effect can be felt in a limited range.

W+, W-, and Z bosons are the weak nuclear force carriers which have their major application in radioactive decay. These forces are so small that their effect of attraction or repulsion can be felt in years. Some examples are beta decay of a nucleus, nuclear fusion, etc.

Photons are the carriers of electromagnetic forces which travel in electromagnetic fields and have a zero charge. They are the packets of energy with zero rest mass that can travel at the speed of light and exhibit their effect in a wider range (possibly infinite). The strength of photons varies strongly with the strength of the magnetic and electric field they are fed to (generally less than strong nuclear forces).

SCALAR BOSONS

The only scalar boson included in the standard model is the Higgs boson (commonly known as the God particle) which is recently discovered by CERN, in 2012 using the world biggest operating machine ‘Large Hadron Collider’. Higgs boson travels in the Higgs field and gives mass to any particle that encounters it. Conversely, every particle gains its mass on interaction with Higgs Boson. Hence the boson is ultimately employed in exerting gravitational forces between the bodies with mass.

Standard-model-2

THE OBSCURE PARTICLE:

Graviton is another important particle whose position is still debatable. The graviton is a hypothetical elementary particle that mediates the force of gravity. While gravitons are presumed to be massless, they would still carry energy, as does any other quantum particle. They are most suitably seated in the last row accompanying Higgs boson. But it has still not found a perfect place in the standard model of particle physics.

Some common term in particle physics:

Hadrons: are composites made of quarks or antiquarks or combination of both. There are two common forms of hadrons called baryons and mesons. The most common examples of hadrons are proton, anti-proton, neutron, anti-neutron, etc.

Bosons-etc

Baryons: are made of three quarks bounded by strong nuclear forces. We can call these as “composites made up of fermions”.

Mesons: are made up of one quark & one antiquark. We can call these as “composites made up of bosons”.

Leptons: are the fundamental particles as listed in the standard model. The most common lepton is an electron.

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