In this work, I examine the roles of the experimental background (effects capable of mimicking the one under study) in cognition, and its relation to the problem of closedness of experimental system. Taking as examples the experiments in particle physics widely discussed in the philosophy of science (discoveries of muon and neutral currents), I suggest that determination of the experimental background often implies an explicit use of components of high-level theories. I argue that the neutron background in the neutral current (...) experiments resulted from the same sort of phenomena as the events in the detector did although those phenomena occurred in the materials surrounding the detector rather than in the detector itself. Therefore, it is justified herein that due to the presence of background experimental outcomes are entertained with theory of phenomenon. (shrink)