How we can know that there are no more particles that graviton and standard model particles??
We DON'T know. What we have is a consistent and useful model of reality that works very well. If/when other particles are discovered, the model will have to be changed. Dark matter may lead to that situation.
Physics builds models based on what is known, not what is unknown.
If you have paid some attention to the LHC results and operations these past 2 years, you would have heard of their search for supersymmetry particles. Clearly, this is an example where high energy physicists ARE trying to see if there are other particles beyond just those within the Standard Model.
What is the probability the existence a particle at our typical energies can exist and a acelerattor can´t detect?
Accelerators do not detect particles. So the probability is 100%.
We don't "know" this at all. The graviton and the Standard-Model particles are the ones that we have had experimental access to. Most supersets of these two theories include additional particles, particles that we may or may not be able to detect evidence of.
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