[BurningFrog]

Then I wonder if this "particle" is just some components that takes 10^-21 seconds to bounce away from each other after colliding?

[ShinyRice]

They don't just "bounce away", some of its quarks turn into different ones through interactions, and that is enough to class that process as a decay.

Also, quarks can't bounce away from each other. Lone quarks do not and cannot exist in nature, as far as we know.