Neutrino Oscillations and Mass,
and CP Violation
The observed oscillations of atmospheric and solar neutrinos show us that neutrinos
have mass, providing the first window on physics beyond the Standard Model.
Already we are able to make strong inferences about neutrino mass and mixing
patterns, which are challenging theoretical ideas about the origin of the mass.
These important discoveries mandate that long-baseline neutrino oscillation
experiments be carried out to determine at what low level muon neutrinos may
oscillate to electron neutrinos and to see if the fundamental symmetries of
CP, T, and CPT are violated in the lepton sector. Matter effects on oscillations
are central to the resolution of inherent parameter ambiguities in oscillation
studies. Supernovae explosions are also a possible route to the one three-neutrino
oscillation mixing angle that is presently unknown. It remains to be experimentally
established whether active neutrinos oscillate to sterile neutrinos. Concurrently,
the absolute scale of neutrino mass will be probed in beta decay, neutrinoless
double-beta decay (if neutrinos and anti-neutrinos are the same particles),
and in cosmology by galaxy surveys of large scale structure and satellite studies
of the cosmic microwave background.
Particle and nuclear physics have strong ongoing programs to probe deeper into
neutrino oscillations. These programs fit well as the initial stages of a future
plan to reach the necessary physics sensitivities. A roadmap for such a plan
is given below:
Stage 0: Current near term program
- NuMI (K2K) checks atmospheric oscillations and measures Dm223 to about 10%
- MiniBooNE makes definitive check of LSND and measures associated Dm2
Stage 1 - Constrain / measure sin22q13
- NuMI / MINOS on-axis probes sin22q13> 0.06 @ 90%CL
- NuMI(JHF) offaxis could go down to sin22q13> 0.01 @ 90%CL
Stage 2 - Measure CP violation and sign of Dm223 with conventional beams
- Must have sin22q13> 0.01
- Need to measure P(nm®ne) and P(`nm®`ne)
- Need increased rate (especially for `n's) Þ Need high intensity proton
sources
Stage 3 - Measurements with Neutrino Factory
- Map out CP violation with precision for sin22q13> 0.01
- Probe nm®ne transitions down to sin22q13> 0.001