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Register a new userConfronting solutions to the atmospheric neutrino anomaly involving large angle $ u_{mu} to u_e$ oscillations with SuperKamiokande and CHOOZ
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Neutrino oscillation scenarios involving large angle $ u_{mu} to u_e$ oscillations are disfavoured in the parameter range $Delta m^2/eV^2 >~ 10^{-3}$ by recent results from the CHOOZ reactor-based $bar{ u}_e$ disappearance experiment. For this reason we extend our previous work on up-down asymmetries for various oscillation scenarios by computing up-down asymmetries and the R ratio for the entire conceivable range $10^{-4} - 10^{-1} eV^2$ of $Delta m^2$. Matter effects in the Earth play a crucial role. We perform a $chi^2$ fit to the data. We find that, because of the matter effect, the three-flavour maximal mixing model provides a reasonable fit to SuperKamiokande and CHOOZ data provided that the relevant $Delta m^2$ is in the range $4 times 10^{-4} ~< Delta m^2/eV^2 ~< 1.5 times 10^{-3}$.
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The $ u_{mu} to u_{tau}$ and $ u_{mu} to u_s$ solutions to the atmospheric neutrino problem are compared with SuperKamiokande data. The differences between these solutions due to matter effects in the Earth are calculated for the ratio of $mu$-like to $e$-like events and for up-down flux asymmetries. These quantities are chosen because they are relatively insensitive to theoretical uncertainties in the overall neutrino flux normalisation and detection cross-sections and efficiencies. A $chi^2$ analysis using these quantities is performed yielding $3sigma$ ranges which are approximately given by $(0.725 - 1.0, 4 times 10^{-4} - 2 times 10^{-2} eV^2)$ and $(0.74 - 1.0, 1 times 10^{-3} - 2 times 10^{-2} eV^2)$ for $(sin^2 2theta,Delta m^2)$ for the $ u_{mu} to u_{tau}$ and $ u_{mu} to u_s$ solutions, respectively. Values of $Delta m^2$ smaller than about $2 times 10^{-3}$ eV$^2$ are disfavoured for the $ u_{mu} to u_s$ solution, suggesting that future long baseline experiments should see a positive signal if this scenario is the correct one.
We study lepton flavour-violating interactions which could result in the $tau$-lepton production in the $ u_{mu}N$ scattering or in $mu to tau$ conversion on nucleons at high energies. Phenomenological bounds on the strength of $bar{tau} u_{mu}bar{q}q^{}$ interactions are extracted from the combined result of the NOMAD and CHORUS experiments on searching for $ u_{mu} - u_{tau}$ oscillations. Some of these bounds supersede limits from rare decays. We also propose a ``missing energy type experiment searching for $mu - tau$ conversion on nucleons. The experiment can be performed at a present accelerator or at a future neutrino factory.
We consider a model where right-handed neutrinos propagate in a large compactified extra dimension, engendering Kaluza-Klein (KK) modes, while the standard model particles are restricted to the usual 4-dimensional brane. A mass term mixes the KK modes with the standard left-handed neutrinos, opening the possibility of change the 3 generation mixing pattern. We derive bounds on the maximum size of the extra dimension from neutrino oscillation experiments. We show that this model provides a possible explanation for the deficit of nu_e in Ga solar neutrino calibration experiments and of the anti-nu_e in short baseline reactor experiments.
We report on a new analysis of neutrino oscillations in MINOS using the complete set of accelerator and atmospheric data. The analysis combines the $ u_{mu}$ disappearance and $ u_{e}$ appearance data using the three-flavor formalism. We measure $|Delta m^{2}_{32}|=[2.28-2.46]times10^{-3}mbox{,eV}^{2}$ (68% C.L.) and $sin^{2}theta_{23}=0.35-0.65$ (90% C.L.) in the normal hierarchy, and $|Delta m^{2}_{32}|=[2.32-2.53]times10^{-3}mbox{,eV}^{2}$ (68% C.L.) and $sin^{2}theta_{23}=0.34-0.67$ (90% C.L.) in the inverted hierarchy. The data also constrain $delta_{CP}$, the $theta_{23}$ octant degeneracy and the mass hierarchy; we disfavor 36% (11%) of this three-parameter space at 68% (90%) C.L.
The excess of solar-neutrino events above 13 MeV that has been recently observed by Superkamiokande can be explained by vacuum oscillations (VO). If the boron neutrino flux is 20% smaller than the standard solar model (SSM) prediction and the chlorine signal is assumed 30% (or 3.5 sigmas) higher than the measured one, there exists a VO solution that reproduces both the observed boron neutrino spectrum, including the high energy distortion, and the other measured neutrino rates. This solution might already be testable by the predicted anomalous seasonal variation of the gallium signal. Its most distinct signature, a large anomalous seasonal variation of Be7 neutrino flux, can be easily observed by the future detectors, BOREXINO and LENS.
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