Neutrinos and nucleon structure

Abstract 'Deep inelastic' collisions of neutrinos and antineutrinos with nucleons behave as if the nucleon Was composed of pointlike constituents (partons and antipartons). Neutrino experiments can measure the net number of (partons-antipartons), their angular momentum and mean square charge; they are 3 in number, have spin 9 and possess the fractional charges postulated ten years ago for the fundamental quarks, by Gell-Mann and Zweig. However, the observation of neutral as well as charged currents in neutrino reactions has compelled introduction of further quantum numbers; for example, a fourth quark with 'charm'. Recent electron-positron collision experiments also suggest new degrees of freedom—'charm' and/or 'colour'. The effects of these and other modifications to the quark model on neutrino cross-sections are discussed.