Three-flavor atmospheric neutrino anomaly

Abstract

We investigate the indications of flavor oscillations that come from the anomalous flavor composition of the atmospheric neutrino flux observed in some underground experiments. We study the information coming from the neutrino-induced $\mu$-like and $e$-like events both in the sub-GeV energy range (Kamiokande, IMB, Fr{\'e}jus, and NUSEX experiments) and in the multi-GeV energy range (Kamiokande experiment). First we analyze all the data in the limits of pure $\nu_\mu\leftrightarrow\nu_\tau$ and $\nu_\mu\leftrightarrow\nu_e$ oscillations. We obtain that $\nu_\mu\leftrightarrow\nu_e$ oscillations provide a better fit, in particular to the multi-GeV data. Then we perform a three-flavor analysis in the hypothesis of dominance of one neutrino square mass difference, $m^2$, implying that the neutrino mixing is parametrized by two angles, $(\psi,\,\phi)\in[0,\,\pi/2]$. We explore the space $(m^2,\,\psi,\,\phi)$ exhaustively, and find the regions favored by the oscillation hypothesis. The results are displayed in a form suited to the comparison with other flavor oscillation searches at accelerator, reactor, and solar $\nu$ experiments. In the analysis, we pay particular attention to the earth matter effects, to the correlation of the uncertainties, and to the symmetry properties of the oscillation probability.Comment: 25 pages (RevTeX) + 12 figures, requires epsfig.sty. All the figures are bitmapped. Postscript figures with full resolution are available at ftp://ftp.sns.ias.edu/pub/lisi/atmpaper

Four-neutrino oscillation solutions of the atmospheric neutrino anomaly

“…3 Assuming ν 4 ∼ ν s in 3+1 models, the triplet states (ν 1 , ν 2 , ν 3 ) would then approximately be linear combinations of (ν e , ν µ , ν τ ), and the triplet phenomenology of solar and atmospheric neutrinos would practically become equivalent to that of a standard framework with three active neutrinos. Such 3ν framework has been worked out in detail in previous papers [32,33,41], where the reader can find the corresponding constraints on the mass-mixing parameters. In conclusion, it seems that the emerging mixing pattern for the 3+1 spectrum implies, up to small "LSND perturbations", an effective three-neutrino phenomenology for solar and atmospheric oscillations.…”

Phenomenology of neutrino oscillations

“…Extensive literature exists on the solar [4,10] and atmospheric neutrinos [5,11]. So, we shall be brief.…”

Erratum: two experiments for the price of one? The role of the second oscillation maximum in long baseline neutrino experiments

“…Even these approximate solutions have a very rich structure; in particular, for fixed energy, any given value of the oscillation probability can typically be realized by different combinations of oscillation parameters. The possible degenerate solutions can be classified into the intrinsic ambiguity [15], the sign of ∆m 2 31 ambiguity [16] and the octant ambiguity [17]. Combined, these three ambiguities give rise to what has become known as the eightfold degeneracy [18].…”