Elementary particle the proton should be uniform and the electron should scatter elastically. Low-energy electrons do scatter in this way, but, above a particular energy, the protons deflect some electrons through large angles. The recoiling electron has much less energy and a jet of particles is emitted. This inelastic scattering suggests that the charge in the proton is not uniform but split among smaller charged particles: quarks. In the Standard Model, vector (spin-1) bosons (gluons, photons, and the W and Z bosons) mediate forces, whereas the Higgs boson (spin-0) is responsible for the intrinsic mass of particles. Bosons differ from fermions in
W and Z bosons particles, starting with and , all denote quarks and antiquarks (factor "N" is applied). The various "V" denote the corresponding CKM matrix coefficients. Unitarity of the CKM matrix implies that Z bosons decay into a fermion and its antiparticle. As the Z boson is a mixture of the pre-symmetry-breaking W and B bosons (see weak mixing angle), each vertex factor includes a factor "T" − "Q" sin"θ" where "T" is the third component of the weak isospin of the fermion, "Q "is the electric charge of the fermion (in units of the elementary charge), and "θ" is the weak mixing