[Physics Class Notes] on Meson Pdf for Exam [2024]

We know that we have many elementary particles available in nature. Elementary particles are those particles that can not be created by other particles. All the elementary particles are classified into two types, Fermions and Bosons. Fermions are the odd half integral spin particle with antisymmetric wavefunctions. Whereas the bosons are the integral spin particles with symmetric wavefunctions. All the elementary particles are classified according to their spin, charge and characteristic behaviours. And they are mainly classified as leptons, mesons and baryons.

Mesons are one of the elementary particles classified under baryons and these are considered to be the heaviest particles and the mesons do not include protons in their decay product. In this article, we will go through a detailed explanation of mesons, meson meaning and what is a meson.

Meson Meaning

Now, let us understand the meaning of Meson. Basically, a meson is a hadronic particle, which means it is having considerable mass. We can define a meson as a fundamental particle that will never decay into a proton or any particles that could subsequently decay into a proton. That means we can say that the mesons will always have comparatively less mass than the protons. Thus, a meson possesses an intermediate mass between the electron and the proton.

The mesons are the fundamental particles or the elementary particles carrying unit charge and possessing mass intermediate between the mass of the electron (m_e) and the mass of the proton (m_p).The name meson was proposed by famous nuclear physicist Yukawa in 1935. The mesons are the hadronic subatomic particles composed of a combination of quark and an antiquark.

What is a Meson?

But, what is a meson? Meson is a fundamental particle categorized under the hadrons. Mesons are the hadronic particles made up of a quark and an antiquark, specifically a meson its own antiparticle. Mesons are the interaction agents between nucleons (protons and electrons). The rest mass of the mesons lies between 250-100mₑ .

The most common type of mesons are the pions (pi mesons), kaons (K mesons) and the eta meson (η-meson).These are also the only types of meson that are long-lived enough to be seen directly by their tracks in a detector.

Pions or The Pi Meson

The pi meson is the lightest type of meson. And they are commonly called the pions.
Pi mesons are composed of up quarks or down quarks and their antiquark counterparts.
Pions are of charge +1, -1, and 0 are denoted π⁺(+e charge), π^–(-e charge), and π⁰(neutral charge), respectively.
The π0 (mass 135 MeV) is composed of either an up or anti up quark pair or a down/anti down quark pair the π+ is an up/anti down pair, and the π– is a down/anti up pair (both have a mass of 140 MeV). All have zero spins.
Pi mesons or the pions were predicted theoretically by Hideki Yukawa in the year 1935, and discovered in cosmic ray experiments on the Pic du Midi by researchers from the Bristol University, England, headed by Cecil Powell, in 1947. They are produced copiously in high-energy particle collisions.

Kaons or K Mesons

A kaon or k meson is a meson that contains one ordinary quark, either an up quark or a down quark and one strange quark.
The K mesons were first discovered in 1947. The k mesons are abbreviated as kaon or the k meson came into use in about 1958.
The k mesons or Kaons come in two varieties: positively charged(K⁺) and neutral (K⁰)and their antiparticles K^– and [bar{K^{0}}] .
They are spin 0 particles, the weight of kaons is about half as much as nucleons, and decay by means of weak interactions.
The charge parity violation was first observed in the k mesons.

Meson Octet

We know that there are a total of eight mesons available in nature and these are arranged in an octet for easier understanding and determination of the charge, strangeness and the spin and it is known as the meson octet structure. Such that along the x-axis we will have isospin of the particles and along the y-axis strangeness. The meson octet is as shown in the below figure.

Did You Know?

Some scientists say that the electron is not an elementary particle (also known as the fundamental particle) and is actually made up of two smaller particles.
Particles made up of the composition of quarks are called hadrons. A bunch of gluons bound together is called a glueball. A tachyon is a hypothetical particle that travels faster than the speed of light.
Quarks and gluons are said to have a coloured charge as well as an electric charge. A proton is made from a composition of blue up quark, a red up quark, and a green down quark