# Compare & contrast properties of strong & weak interactions

• Flucky

#### Flucky

Hi all - in the question below I could do with some help on the "..explanation for the relative strengths..." bit, as I can't think of anything to say.

1. Homework Statement

Compare and contrast the properties of the strong and weak interactions. Include in your account an explanation for the relative strengths of the interactions, the types of particles affected by each interaction and other distinguising characteristics.

-

## The Attempt at a Solution

Weak interactions can involve all leptons and quarks, and are mediated by W± or Z bosons; whereas strong interactions can only involve quarks (binding them as hadrons) and are mediated by gluons. The strength of the weak interaction falls of with distance (~10-2 at 10-18 m to ~10-13 at 10-15 m) which is opposite for the case of the strong interaction (~1 at large distances to <1 at small distances). Weak interactions can also violate conservation laws such as parity, strangeness and isospin - which the strong interaction cannot.

The question is worth 4 marks (which I know doesn't mean much out of context) so I think I would need to cover the main aspects of each. As I said above I am not sure what to put for the explanation for the relative strengths.

Cheers.

Bump

For those who might read this in future, my lecturer came back to me with a few things more that should be said:

Gluons are massless, leading to a long-range force. They couple to colour (carried by quarks) and also carry composite colour, so can interact with each other, which leads to colour-screening effects at short distance. The strength of the force therefore increases with increasing distance (or decreasing momentum transfer).
(The strong interaction can involve hadrons - particles made of quarks - not just the bare quarks themselves.)
The W & Z are very massive (80-90 GeV/c^2), leading to a very short range. (You do give the fall with distance.) At very short distances (10^-18 m), the strength is no less than the EM interaction.