# Why could the Tevatron collider only exclude high masses of the Higgs boson?

I wish to know why the Tevatron collider could only exclude high masses of the Higgs boson ($158-175~\rm{GeV/c^2}$). The two mainly facts you must to consider are that the Tevatron uses energies off $2~\rm{TeV}$ in mass center and that it collide protons with antiprotons.