Or not. But we are either sure or almost sure depending on your standard of certainty that the Higgs Boson has been detected by CERN and therefore that we have evidence of the Higgs field, the theory that explains mass as a result of elements interaction with the Higgs field.

PhD Comics has this very cool video explaining not only Higgs but several aspects of the standard model:

The Higgs Boson Explained from PHD Comics on Vimeo.