Conventional Beams or Neutrino Factories: The Next Generation of Accelerator-Based Neutrino Experiments

The purpose of this paper is to provoke a discussion about the right next step in accelerator-based neutrino physics. In the next five years many experiments will be done to determine the neutrino mixing parameters. However, the small parameters $\theta_{13}\Delta m_{21}^2$, and the CP violating phase are unlikely to be well determined. Here, I look at the potential of high-intensity, low-energy, narrow-band conventional neutrino beams to determine these parameters. I find, after roughly estimating the possible intensity and purity of conventional neutrino and anti-neutrino beam, that $\sin^2\theta_{13}$ can be measured if greater than a few parts in ten thousand, $\Delta m_{21}^2$ can be measured if it is greater than $4\times 10^{-5}$ (eV)$^2$, and the CP violating phase can be measured if it is greater than 20$^\circ$ and the other parameters are not at their lower bounds. If these conclusions stand up to more detailed analysis, these experiments can be done long before a muon storage ring source could be built, and at much less cost.