What Is an Antiparticle?

As the advancements taking place in physics have been getting better and more interesting to know about the universe. We know that atoms are made up of protons, neutrons and electrons. These were assumed to be extremely small and massless particles. After a period of time scientists were able to discover particles that are also constituents of the atom and categorized them as elementary particles. The group of elementary particles have particles and their antiparticles. 

Now, what are the antiparticles? We know that the universe is made up of several particles such as electrons, protons, neutrinos, etc… all these particles are having their corresponding antiparticles associated with them, such that the interaction of these particles will destroy each other and hence it will lead to extreme energy release in the form of photons or sometimes in the form a new particle. These antiparticles will be having the same mass as the particle but different physical and quantum properties.

Antiparticle of Electron:

So, whenever we speak about particles, the most basic and important particle is an electron. The electron is also having its corresponding antiparticle known as the anti-electron or the positron. According to the antiparticle definition, we know that it is such a particle when it reacts with its corresponding particle will lead to annihilation resulting in a large energy release. 

Therefore, the antiparticle of the electron is a positron, such that when an electron interacts with the positron both will get destroyed resulting in extreme energy release in the form of a photon. The positron is denoted by e+. An electron is negatively charged and the antiparticle of the electron is positively charged.

Now, let us have a look at what actually happens when an electron is interacting with the positron. So, when an electron interacts with the positron the energy will be released in the form of two gamma photons that will be carrying the rest mass energy of these particles to conserve the linear momentum.

⇒ e⁻ + e⁺ → γ + γ …….(1)

Both the gamma photons will be having excess energy of 0.511 MeV (which is nothing but the rest mass of the electron and the positron) and also if both the particles have some initial kinetic energy that will also be carried forward by these two. These pair annihilation will correspond to various conservations, such as during these reactions total charge of the system will be conserved, the total energy is conserved, total linear momentum is conserved, etc… 

Let us have a look at some properties of the electron and antiparticle of electron:

1. Both electrons and the positron are having the same rest mass energy given by 0.511 MeV.

2. The antiparticle of an electron is having an opposite charge, i.e., it is positively charged whereas the electron is a negatively charged particle. This is because to conserve the charge. 

3. The electron and its antiparticle are having the same spin. The electrons are the fermions and hence it is having a half-integral spin and hence the antiparticle of the electron is also having a half-integral spin.

4. The electron and its antiparticle are having an opposite magnetic moment. The electron is having a negative magnetic moment whereas the positron is having a positive magnetic moment. The magnetic moment is the property of elementary particles that describes how the particles interact with the external magnetic fields. 

5. Electrons and the antiparticle of electrons are having opposite lepton number. The lepton number of the electron is 1 and the lepton number of the positron is -1. 

These are some important properties that elaborate the relation between the electron and antiparticle of an electron.

Antiparticle of Proton:

Just like the electron had its own antiparticle, the proton is also having an antiparticle associated with it. The antiparticle of proton is known as the antiproton and it is denoted by p̅. Unlike electrons, protons are not elementary particles, protons are composite particles made up of elementary particles known as the quarks and hence the annihilation of these particles will be quite difficult in comparison with the annihilation of other elementary particles. 

So, as mentioned the protons are not the actual elementary particles, but they are the composite particles made up of further elementary particles known as the quarks. Protons are made up of the composition of two up quarks and one down quark, at the same time antiproton is made up of two anti up quark and one anti down quark. I.e., we write:

⇒ Proton = u u d

⇒ Antiproton = u̅ u̅ d̅

Now, when the proton interacts with the antiproton the annihilation of the quarks takes place. Thus the annihilation or the interaction of proton with its antiparticle is considered to be one of the complicated reactions. 

Let us have a look at some properties of the proton and antiparticle of proton:

1. Both proton and the antiparticle of the proton are having the same mass.

2. The antiparticle of the proton is having an opposite charge, i.e., it is negatively charged whereas the proton is a positively charged particle, without violating the law of conservation of charges. 

3. The proton and its antiparticle are having the same spin. The protons are the fermions and hence it is having a half-integral spin and hence the antiparticle of the proton is also having a half-integral spin.

4. The proton and its antiparticle are having an opposite magnetic moment. The proton is having a positive magnetic moment whereas the antiproton is having a negative magnetic moment. The magnetic moment is the property of elementary particles that describes how the particles interact with the external magnetic fields and the direction of alignment of the particle. 

5. The proton and the antiparticle of the proton are having opposite baryon number. The baryon number of the proton is 1 and the lepton number of the antiproton is -1. 

These are some important properties of the proton and the antiproton. This explains how the particle and antiparticles are associated with each other. Similarly, all other elementary particles are having their corresponding antiparticles such as the neutrino is having antineutrino, i.e., the neutrino antiparticle is antineutrino denoted by \[\bar{v_{0}}\]. Basically, the antiparticle theory explains the interaction between the elementary particles and the conservation of laws.

Did You Know:

In recent times we have discovered a new elementary particle known as the Higgs boson. According to antiparticle theory, all the elementary particles are having their corresponding antiparticle, then what is Higgs boson antiparticle, it is not possible. Higgs boson will not have an antiparticle even though it is an elementary particle. Higgs boson is considered to be a god particle and all other elementary particles are its constituents.