original: The Higgs boson is the only Standard Model particle that has not yet been observed.
simplifications: The Higgs boson is the only particle the hasn't been discovered. No one has seen the the Higgs boson. The Higgs boson is the only Standard Model particle that has never been seen. The Higgs boson is the only Standard Model particle not yet observed. The Higgs boson is the only Standard Model that has not yet been seen. The Higgs Boson is a Standard Model particle. It is the only Standard Model particle that has never been observed. The Standard Model particle, Higgs boson, has yet to be observed The Higgs boson is the only Standard Model particle not yet observed. The Higgs boson is the only Standard Model particle that has not been observed. The only Standard Model particle not to be seen is called the Higgs boson.