The Standard Model of elementary particles 2: Gauge Bosons

There are four fundamental interactions in the universe: gravitational force, electromagnetic force, strong nuclear force and weak nuclear force. Standard Model includes all but gravitational force. These interactions included in the Standard Model are carried out by their corresponding force carriers, or gauge bosons: photons, gluons and W and Z bosons.

Electromagnetic force and photons is the most well-known pair. Photon has been proven to exhibit  wave-particle duality: it can show the property of either particle or wave depending on the means of observation. On the one hand, a photon can be reflected by an object, refracted in a medium and diffracted by a slit like normal waves such as water waves. On the other hand, the position of a photon and the energy each photon carries can be measured just as that of a particle. Therefore, when an electron and a positron annihilate, the energy is released in the form of gamma ray, a rather energetic electromagnetic wave, that radiates away from the point of annihilation.

Gluons are the force carriers of strong nuclear force. Just as the electromagnetic force is produced by the exchange of photons between electrons, the strong nuclear force is produced by the exchange of gluons between quarks. The widely used analogy pictures one person on a frictionless surface tossing a basketball to another one. As the first person pushes the basketball into the air, the force is transmitted to and carried by the basketball and is later passed on to the second person. A video link is attached below to help visualized the process. The strong nuclear force is the strongest of all three interactions described by Standard Model and is also stronger than gravitational force. The main contribution of strong nuclear force is that it neutralized the electromagnetic repulsion between the protons within the nucleus. In fact, the strong nuclear force is so powerful that if one tries to isolate a pair of quarks A and B, one has to spend a great amount of energy enough to create another pair of quarks B’ and A’ that will respectively be paired with the original quarks A and B as soon as they break apart. Thus, the strong nuclear force is able to defend the notion of color confinement. Moreover, most of the mass of a proton or neutron is represented in the form of the strong nuclear force field energy whilst the individual quarks provide only about 1% of the mass of a proton.

Weak nuclear force is the carried out by W bosons and Z boson. W boson carries -1 electric charge and has its antiparticle W+ boson while Z boson has no charge. All quarks and leptons interact through weak interaction by means of emitting and absorbing W and Z bosons. The W and Z bosons are heavy bosons that each weighs more an iron atom. This brings instability to the particles and thus the particles are short-lived. The weak nuclear force is also short-ranged due to the mass of its force carriers and is the weakest among all the interactions.

Neutron undergoes beta decay.

Neutron undergoes beta decay shown by the Feynman Diagram .

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