Standard Model -Elementary Particles

Every day we hear about the LHC experiment in the news.
Physicists talk strange language when it comes to describing their work which sounds like greek for most people. But Steven Weinberg one of the most important particle physicist of the 20th century had often proclaimed that most physics concepts can be explained in simple terms.

In order to completely comprehend what is going on at the LHC(Large Hadron Collider), the biggest scientific experiment of mankind ever, you need to understand many concepts in physics.
From the wildest ideas like SUSY (Supersymmetry) to the darkest matter in the universe, from the higgs bosons to black holes, stranglets to antimatter and so on.
What are these people talking about?.
Let us discuss Higgs boson first. Since we have lot of ground to cover we will take it in steps.

Physicists build models of the universe. A model is nothing but a possible blueprint of reality. From a model comes predictions. Predictions need to be verified. If a model cannot produce predictions that can be verified, it is not worth its money. It would be promptly thrown away.
But when a model survives the acid test of experimental verifications, it becomes accepted and the model leads to further refinements and so on.
What science believes is that , the closer it is to reality better is its chance for survival from experimental verifications . Science is an asymptotic progression towards reality .
Basic questions about the universe are no longer a passtime but are part of serious investigations.

As far as the Higgs boson is concerned, it is one of the predictions of the Standard model.

Now what is the Standard Model?.

It is the Model that Physicists have built over a period of time for understanding what matter is made up of and how different things interact.

If you look at ancient civilizations, you can observe that they all had a concept about some fundamental entities out of which all matter is made up. For e.g. in the greek and indian philosophies it was postulated that the whole world is made up of primary elements such as earth, air, fire, and water.

From there on science advanced, but it was only in the 1900s that physicists came up with the idea of the atom as the indivisable unit that constitues matter. It was speculated the entire universe could be thought of as made up of only 92 different kinds of atoms.
This can be called the Atomic Model .
Based on this model came predictions which were verified again and again.
All the physical and chemical properties of substances were the result of atomic configuration of that substance.
Each atom has an atomic number. For e.g. Hydrogen is the first atom and it has an atomic number 1 and Uranium is 92nd atom.
Atoms were arranged nicely in a table called the Periodic table. Why the name Periodic table?.
This is because chemical properties of atoms exhibit a regualarity.
Now this lead many people think that may be the atom is not fundamental after all. Maybe there are more fundamental elements out of which the atom is made up and different combinations of these elements lead to different atoms. So instead of 92 different kinds of atoms, physicsts started dealing with only 3 different entities
1) Electrons
2) Protons
3) Neutrons

The protons and neutrons make up the central part of the atom called the Nucleus and electrons move around the nucleus and are arranged in fuzzy orbits.
All the different atoms are made up of different set and configuration of these entities.
Thus the Hydrogen atom has only a single electron and a proton while
the uranium has 92 electrons , 92 protons and 146 neutrons

Isnt it amazing to think that the whole world is just made up of 3 basic elements?.
However this cozy picture of the universe was shattered when cosmic rays were discovered.
Cosmic rays are showers of different particles bombarding the earth's atmosphere.
Cosmic rays are the Natural Particle accelerators!!!.

From a simplistic picture there was a profusion of elementary particles.
there were pi mesons, K particles, omega hperons and so on.
If there is a multitude of entities, the first thing scientists do is to classify them into nice groups.
Classification can be done in many ways in the case of particles.
If you classify them in terms of mass. There are heavy particles
called Hadrons, medium wieght particles called Mesons and light weight particles called Leptons.
A simple example of Hadron is the proton and that of lepton is the electron.
It was soon found that there were lot of hadrons and mesons while the Leptons were few in number. So maybe hadrons and mesons are not fundamental after all?.
It was postulated that the Hardons and mesons were thought of as consisting of simpler entities called Quarks.
Thus for example a Proton has a structure
p -- uud ( 2 up quarks and a down quark)
while the neutron ( 2 down quarks and a down quarks)
n -- udd

So the only difference between a proton and a neutron is that in a neutron a down quark is there for an up quark.
So in the 1960s physicists discovered that the whole zoo of particles( hundreds of them) could be thought of as consisting of simply 2 sets of particles
1)Quarks
2)Leptons
Quarks are of six types ( up, down, charm, strange, top and bottom)
Leptons are also of six types ( electron and its neutrino , muon and its neutrino , tau and its neutrino).

Since most atoms are made up of neutrons, protons and electrons we can see that they are made up of the up quark , down quark and the electron .
The other zoo of particles require different combinations of the other quarks but they occur very infrequently in the universe.
So most of the universe can be constructed out of
u quark
d quark and
electron.

In addition to this there is also the conept of antimatter. Antimatter is the mirror image of matter. This is also something that came out of a model and it was experimentally observed.

Thus the antimatter counterpart of the electron is called the anti electron or positron , the up quark has an anti up qaurk and so on.

From what we have said so far you can easily find out that the anti proton would be made up of
anti u , anti u and anti d.

When matter and anti matter meet they annihilate into pure energy.

It has been repeatedly shown that this picture is accurate to a large extent and can explain many phenomena in the Universe. You cannot break these particles to smaller entities even at very high energies found in Ultra big Particle Accelerators like the LHC.

Having understood about the fundamental particles , Let us talk about their interactions in the next dose.