Particle physics is the study of Particles, from what everything is made of. In this section of physics we study the fundamental particles that make up all of matter, and their mutual interaction.
Everything around us is made up of these particles, you may say, made up of fundamental building blocks of nature. So, what are these building blocks?
In the early nineteenth century, it was believed that atoms were fundamental; they were thought to be the smallest part of nature and were not made up of anything smaller.
After a sharp progress in Physics, experiments discovered that atoms were not fundamental at all, but were made up of two components:
• Positively charged nucleus
• Negatively charged electrons, surrounding the nucleus.
Then the nucleus was probed to see if it was fundamental, but it too was discovered to be made up of something smaller; positive protons and neutral neutrons bound together with the cloud of electrons still surrounding it.
Now that these protons and neutrons were found, it was time to see if they were fundamental. It was discovered that they were made up of smaller particles called “quarks”, which today are believed to be truly fundamental, along with electrons. Furthermore, electrons belong to a family of fundamental particles, which are called “leptons”. Quarks and leptons, along with the forces that allow them to interact, are arranged in a nice neat theory named The Standard Model.
The Standard Model
The Standard Model is a standard in particle physics. It’s a theoretical picture that describes how the different fundamental particles are organized and how they interact with each other along with the different forces.
What is in it?
Briefly it states that:
The elementary particles are split up into two families, namely the quarks and the leptons. Both of these families consist of six particles, split into three generations, with the first generation being the lightest, and the third the heaviest. Furthermore, there are four different force carrying particles which lead to the interactions between particles.
The table below shows this all a little bit more clearly.
An interesting thing that has been discovered about matter particles, is that each one has a corresponding antiparticle.
The term “anti” may be a bit deceiving, as it is still real matter. The only difference between a particle and it’s antiparticle is that an antiparticle has the opposite electrical charge.
Think of it as a mirror image. In our experience left and right are the only things to reverse when looking in the mirror. Similarly, in the particle world, charge is what reverses when looking in the “mirror”. This has mass, spin, and most other (quarks have something called color charge which is also changed in the “mirror”) properties the same.
he antiparticle of the proton is the anti-proton. An exception to this rule is the electron, whose antiparticle is known as the positron, not anti-electron.
In high-schools, we read that the electric charge can’t be rationalized. That meant any charge can only be an integer multiple of electron’s charge i.e., 1.6 x 10-19 Coulombs. But discovery of quarks denied this concept.
Mainly, there are six types of quarks, in three regular pairs:
1. Kindly note that there are also six – anti-quarks:
• Anti Up & Anti Down Quarks
• Anti Charm & Anti Strange
• Anti Top & Anti Bottom
Top- Bottom are sometimes called Truth- Beauty.
3. You should know that there is no existence possible of a single Quark. That’s why we generally write Quarks. These form composite particles after combining, called Hadrons.
4. As mentioned, Quarks, like protons and electrons, have electric charge. However, their electric charges are fractional charges, either +2/3 or -1/3 (-2/3 and +1/3 for antiquarks), and they always arrange to form particles with an integer charge (ie. -1, 0, 1, 2…). Because quarks join with each other to form particles with integer charge, (i.e. HADRON, what earlier mentioned) not every kind of combination of quarks is possible.
There are two basic types of Hadrons:
• Baryons: These are composed of three quarks
• Mesons: These are made up of two quarks, a quark and an anti-quark.
Examples of baryon are the neutron and the proton.
The proton is composed of two up quarks and one down quark. As you can see, in the image, when the charges from the individual quarks are added up, you arrive at the familiar charge of +1 for the proton.
The neutron is made up of two down quarks and one up quark.
Adding the charges from the quarks up, we arrive at zero.
An example of a meson is the pion or $\pi$ – meson.
The pion is composed of an up quark and a down anti-quark. Because mesons are a combination of particle and antiparticle, they tend to be very unstable and decay very quickly.