After symmetry breaking, the masses of the W and Z are given by m W = 1 2 g v and m Z = 1 2 g 2 + g ′ 2 v , which can be viewed as predictions of the theory. The photon remains massless. The mass of the Higgs Boson is m H = 2 μ μ 2 = 2 λ λ v . Since μ μ and λ λ are free parameters, the Higgs' mass could not be predicted beforehand and had to be determined experimentally.