Introduction to Elementary Particles

Cosmological Research on Elementary Particles and Forces

Particle Accelerator

Near Geneva (on the Swiss-French border) stands the Large Hadron Collider (LHC), a super-large, underground particle accelerator.
The LHC has a circumference of 27 kilometers and is located about one hundred meters below ground.
In a particle accelerator, processes at the microcosmic level are investigated, which can tell us something about processes at the macrocosmic level.
Here, scientists accelerate elementary particles, such as protons (= hydrogen nuclei), to almost the speed of light. At that speed, protons go through those 27 km 11,000 times per second.
Researchers collide hydrogen nuclei with another beam of protons traveling in the opposite direction. These collisions take place between gigantic detectors. These detectors work like digital cameras.

With these, scientists recreate the conditions as they were less than a billionth of a second after the beginning of the universe, up to 600 million times per second inside such a detector. With the help of immense magnets, the electrically charged particles are deflected, so that researchers can measure how fast they are going. With such a super-collider, mini Big Bangs are created, as it were. 

Why do physicists try to mimic the conditions of less than a billionth of a second after the universe began?
The goal of particle physics is to understand what everything is made of and how everything is connected. By 'everything' is meant: molecules, humans, all life forms, the earth, the sun, as well as the hundred billion suns in our galaxy and the hundred billion galaxies in the observable universe.

Elementary Particles and Forces

Cosmologists realized that if you look back in time, the universe becomes hotter and hotter, denser and denser, and simpler and simpler. Long ago, in the early days of the universe, matter and space must have been very simple and understandable.

Today, the cosmos is made up of the following: Only twelve elementary particles, held together by four fundamental forces.
Quarks are the particles that make up protons and neutrons, the constituents of all atomic nuclei in your body. The electron is the particle that orbits the atomic nucleus. The electron is held in its orbit by the electromagnetic force, which is transmitted by another elementary particle: the photon. The quarks are held together by other particles called gluons.

Of the four forces, the 'weak nuclear force' is probably the least known. When the sun shines, enormous amounts of certain particles are emitted: neutrinos. Without those particles, the sun would not shine. About 60 billion neutrinos per second (from the sun) pass through every square centimeter of your body. But you don't feel them, because of this weak nuclear force. The weak nuclear force works over a very short distance and is very weak, which is why neutrinos fly right through your body.

Most particles have been discovered in the last century or so. The first, the electron, was discovered in 1897 and the last, the tau neutrino, in the year 2000.
The greatest scientific achievement of the 20th century is the discovery of the patterns of elementary particles, and the shaping of the laws of particle physics. This is called the 'standard model' which consists of a wondrous, but very long mathematical equation, which is not written out in this book.

Diagram A: Twelve Elementary Particles and 4 Forces.

Standard Model of Elementary Particles

The Standard Model is a framework that describes the known fundamental particles and forces, except gravity.
This model can be written out in a very long mathematical equation.
It is beyond the scope of this book to present that formula here.

Simplified Explanation

Imagine the universe as a play with different actors (Elementary Particles) and rules (Fundamental Forces).
The Standard Model is the script that describes how these actors interact with each other.
The Higgs boson is like a "glue" that makes some particles heavier than others.
Supersymmetry is like a mathematical "expansion pack" for the script, adding more actors and rules to explain some unsolved mysteries.

Higgs Particle

The mathematical equation of the Standard Model allows scientists to calculate everything except gravity.
In that formula, there is also a symbol H. The H stands for the Higgs particle. Higgs particles have only recently been discovered (in 2012), which makes the formula now correct. The Higgs particle gives mass to the fundamental particles.
The general assumption is that the entire universe -and that means not only cosmic space, but also the space within myself and within you- the entire universe, is filled with something called the Higgs field (or Higgs bosons).

Problems

There is another problem: the forces in nature, if you go back in time, seem to change in strength:
The electromagnetic force, the force that holds us together, becomes stronger at higher temperatures.
The strong nuclear force, which holds atomic nuclei together, becomes weaker.
In the standard model, one can calculate how the forces change and plot this on a graph with 3 lines.
Then the three forces (excluding gravity) seem to almost come together at one point. It's almost as if there was one kind of super force when the universe was created. However, in the graph, the 3 lines do not quite touch.

Supersymmetry

There is a theory called supersymmetry, in which the number of particles in the standard model doubles.
At first glance, that doesn't sound like a simplification, but with this theory, we see that the natural forces do come together exactly in the graph at the moment of the Big Bang.
Also, those supersymmetry particles are very good candidates for dark matter. So this is a very strong theory that is widely accepted.

Conclusion

So, the Higgs boson plays a crucial role in explaining mass. The Higgs field permeates space and gives mass to particles that interact with it.
It is important to emphasize that the Standard Model is very successful, but also incomplete. For example, it does not explain dark matter or gravity.
Supersymmetry is a theory that extends the Standard Model. It predicts that every known particle has a "superpartner".
Supersymmetry could indeed explain the unification of forces at high energies.
It is also the case that supersymmetric particles are good candidates for dark matter.
It is important to note that supersymmetry has not yet been confirmed experimentally. Scientists are still searching for evidence for the existence of superpartners.
Dark matter is a hypothetical form of matter that makes up about 85% of the matter in the universe. Dark matter does not emit light or other electromagnetic radiation.