Why do particles decay and what processes are involved?

[Khadija Motala]

why is that particles such as the tau muon have a short lifespan and why is it that particles decay into other partcles? furthermore, what are the process that occur in particle decay?

 

[mfb]

Physics cannot explain "why" - it can just describe the observations. Tau particles have a possible decay, and it is possible to calculate their lifetime (based on other values, like the muon lifetime), but that does not answer why they decay.
Concerning "how": Well, it can be described as interaction with the W boson.

 

[AbsoluteZer0]

what are the process that occur in particle decay?

In the standard model there are several fundamental forces of nature:Strong Nuclear Force

-Responsible for binding quarks together as well as protons and neutrons​

Weak Nuclear Force

-Responsible for all radioactive decay​

Electromagnetic Force

-Occurs between everything that has a charge.​

**Gravity has been debated over the years

Each of these forces has a corresponding particle known as a gauge boson that is responsible for carrying out those forces. The Strong Nuclear force is carried out by the Gluon, the Weak Nuclear force is carried out by the W and Z bosons (the W boson has positively charged and negatively charged variants,) and the Electromagnetic force is carried out by the Photon.

In the case of radioactive decay, all radioactive decay occurs as a result of the weak nuclear force. The weak nuclear force is important as it is the only known force that has the potential to change the flavor (characteristics) of a quark. Take, for example, the decay of a proton into a neutron.

A proton is composed of two up quarks and a down quark and a neutron is composed of two down quarks and an up quark.
p → n + w⁺
The w⁺ boson then decays into a positron e⁺ and an electron anti neutrino ̅νe.
So: p → n + e⁺ + ̅νe.
The positron and antineutrino conserve charge. As a result of the interaction with the w⁺ boson, one of the up quarks changes into a down quark.

http://en.wikipedia.org/wiki/Standard_Model

 

[mfb]

Weak Nuclear Force

-Responsible for all radioactive decay​

Not all, just beta decays.

Alpha decays, gamma "decays", proton emission, neutron emission, cluster decays and fission are independent of the weak force.