Long Baseline Neutrino Oscillation Review

The most exciting result of the last decade has been the growing evidence that neutrinos are massive. The V-A structure of the electroweak theory requires only left handed and therefore massless neutrinos. Observation of neutrino mass is therefore in direct conflict with the Standard Model. The most important result, indicating that neutrinos do oscillate and therefore have to have mass, comes from the Super Kamiokande experiment. They observed a zenith angle dependence (and thus a dependence on distance travelled) in the ratio of νμ to νe interactions of atmospheric neutrinos . Since the angular dependence is far larger than the asymmetry in the cosmic ray flux, there is no known way of generating this effect other than neutrino physics. In addition the angular dependence is described by oscillation parameters consistent with the measured suppression of the total νμ to νe ratio. The angular dependence at Super Kamiokande implies that the value of ∆m, the difference in the mass squared of the two neutrinos, lies between 10 and 10eV. The data from other experiments confirms this observation.