Kaons are mesons composed of a quark and an antiquark. They are indeed formed by the combination of matter and antimatter particles, which would typically lead to annihilation if they were to directly interact.
However, the reason kaons can exist for a relatively long time before decaying is due to the nature of the strong force, which is mediated by particles called gluons. The strong force is responsible for holding quarks together inside hadrons, such as protons and neutrons. It is a very powerful force that binds the quarks tightly and prevents them from annihilating with their corresponding antiquarks.
In the case of kaons, they are primarily held together by the strong force, which keeps the quark and antiquark bound together. The annihilation of the quark and antiquark would require them to come very close to each other, but the strong force prevents this from happening. However, the strong force does not completely suppress the weak force, which is responsible for the decay of the kaon.
The weak force is responsible for processes such as the transformation of one type of quark into another, and in the case of kaons, it leads to their decay. The weak force is weaker than the strong force, and eventually, after a certain amount of time, it can cause the kaon to undergo decay into other particles through weak interactions.
The specific decay processes of kaons are governed by the laws of quantum mechanics and the associated probabilities of different decay channels. These probabilities determine the average lifetime of the kaon before it decays. The half-life of a kaon is the time it takes for half of a large number of kaons to decay.
So, while the combination of matter and antimatter particles in a kaon would generally lead to annihilation, the strong force keeps them bound together long enough for weak decays to occur and give the kaon a finite lifetime.