What is needed?

For the future, one wants to establish neutrino oscillations (or constrain small admixtures of other effects in hybrid scenarios), establish which mixing scenarios are occurring, and determine the neutrino properties. In particular:

• It is very imporant to actually observe a neutrino oscillation (or at least a dip) consistent with the characteristic $L/E$ dependence. The dedicated MONOLITH experiment [41], or a future $\nu$ factory should be able to do this cleanly. Long baseline experiments (K2K [42], MINOS [43], ICARUS [44,45]) may also observe oscillation patterns, as may the full (two detector) BOONE [33].
• One wants to determine the number of neutrinos and their nature, e.g., are there sterile neutrinos, and are the active neutrinos Dirac or Majorana? Mini-BOONE [33] should be able to confirm or eliminate the LSND results, clarifying the need for sterile neutrinos. $\beta \beta_{0\nu}$ may help resolve the Dirac/Majorana issue, although only for some mass/mixing patterns.
• The neutrino mass and mixing spectrum is important for its theoretical implications, for choosing the solar neutrino solution, and for possible astrophysical implications. It will be difficult to observe the absolute scale of the spectrum, but some improvement may still be possible from $\beta \beta_{0\nu}$ and from kinematic (laboratory [46] and, especially, supernova [47]) observations.
• It may be possible to confirm that the atmospheric neutrino effects are mainly due to $\nu_\mu \mbox{$\rightarrow$}\nu_\tau$ by $\tau$ appearance in future long baseline experiments (or possibly in atmospheric observations), but it will be harder to constrain small admixtures of $\nu_s$.
• Leptonic CP violation is of theoretical interest. This may be observable (depending on the parameters) at a neutrino factory or possibly a superbeam.