Ok, so something must exist and how it interacts would explain observations (or measures) but science doesn't say what it is. It predicts what will be observed, from experimental setup, initial conditions and the kind of measure that would be carried out without committing to the existence of any particular thing. So physicists do believe there is something that exists beyond the value measured in a particular setup but science doesn't say what it is exactly. So any description involving the notion of particle would be only a manner of speaking, not an actual commitment to the existence of a particle as such. Right?
EB
I can't figure out what you are trying to say. "Not an actual commitment to the existence of a particle"??? Hell yes there is. We state what a particle's mass, charge, spin, energy, position, etc. is. If that isn't committing to its existence then I have no idea what you are calling "existence". If you don't think this is committing to its existence, then you certainly are using a different meaning for existence. It isn't what I mean by existence, isn't what science means by existence, and isn't what is meant by the common usage of the term.
Do you mean that if a particle is too small to see directly without instrumentation then it doesn't exist? If so, that is a damned weird definition, it would mean that viruses don't exist.