C. Argüelles

First Constraints on the Complete Neutrino Mixing Matrix with a Sterile Neutrino

Neutrino oscillation models involving one extra mass eigenstate beyond the standard three (3+1) are fit to global short baseline experimental data and the recent IceCube ν_{μ}+ν[over ¯]_{μ} disappearance search result. We find a best fit of Δm_{41}^{2}=1.75u2009u2009eV^{2} with Δχ_{null-min}^{2}/d.o.f. of 50.61/4. We find that the combined IceCube and short baseline data constrain θ_{34} to <80°(<6°) at 90%xa0C.L. for Δm_{41}^{2}≈2(6)u2009u2009eV^{2}, which is improved over present limits. Incorporating the IceCube information provides the first constraints on all entries of the 3+1 mixing matrix.

Sterile neutrino fits to short baseline data

Abstract Neutrino oscillation models involving extra mass eigenstates beyond the standard three ( 3 + N ) are fit to global short baseline experimental data. We find that 3 + 1 has a best fit of Δ m 41 2 = 1.75 eV 2 with a Δ χ null - min 2 (dof) of 52.34 (3). The 3 + 2 fit has a Δ χ null - min 2 (dof) of 56.99 (7). For the first time, we show Bayesian credible intervals for a 3 + 1 model. These are found to be in agreement with frequentist intervals. The results of these new fits favor a higher Δ m 2 value than previous studies, which may have an impact on future sterile neutrino searches such as the Fermilab SBN program.

Lowering IceCube’s energy threshold for point source searches in the southern sky

Observation of a point source of astrophysical neutrinos would be a smoking gun signature of a cosmic-ray accelerator. While IceCube has recently discovered a diffuse flux of astrophysical neutrinos, no localized point source has been observed. Previous IceCube searches for point sources in the southern sky were restricted by either an energy threshold above a few hundred TeV or poor neutrino angular resolution. Here we present a search for southern sky point sources with greatly improved sensitivities to neutrinos with energies below 100 TeV. By selecting charged-current ν μ interacting inside the detector, we reduce the atmospheric background while retaining efficiency for astrophysical neutrino-induced events reconstructed with sub-degree angular resolution. The new event sample covers three years of detector data and leads to a factor of 10 improvement in sensitivity to point sources emitting below 100 TeV in the southern sky. No statistically significant evidence of point sources was found, and upper limits are set on neutrino emission from individual sources. A posteriori analysis of the highest-energy (∼100 TeV) starting event in the sample found that this event alone represents a 2.8σ deviation from the hypothesis that the data consists only of atmospheric background.