NuFit-6.0: Updated global analysis of three-flavor neutrino oscillations

TL;DR

NuFIT-6.0 delivers an updated global analysis of three-flavor neutrino oscillations using data through September 2024, highlighting precise measurements of θ12, θ13, Δm^2_21, and |Δm^2_3ℓ| and revealing persistent θ23 octant ambiguity. The leptonic CP phase δ_CP exhibits strong dependence on the mass ordering, with NO favoring CP conservation within 1σ and IO preferring δ_CP ≈ 270° with significant CP-violation indications; MO discrimination remains modest in the global fit, though it strengthens to Δχ^2 ≈ 6.1 when atmospheric data are included. T2K and NOvA appearance data lean toward NO in some combinations but IO remains competitive when considering the full data set, while disappearance data push the preference toward NO, illustrating complex inter-dataset tensions. The analysis also provides updated projections for absolute-mass observables, highlighting robust solar-sector results under updated Standard Solar Models and incorporating SNO+/KamLAND data, with strong correlations among mνe, Σmν, and mee that constrain the allowed mass scale in the 3ν framework.

Abstract

We present an updated global analysis of neutrino oscillation data as of September 2024. The parameters $θ_{12}$, $θ_{13}$, $Δm^2_{21}$, and $|Δm^2_{3\ell}|$ ($\ell = 1,2$) are well-determined with relative precision at $3σ$ of about 13\%, 8\%, 15\%, and 6\%, respectively. The third mixing angle $θ_{23}$ still suffers from the octant ambiguity, with no clear indication of whether it is larger or smaller than $45^\circ$. The determination of the leptonic CP phase $δ_{CP}$ depends on the neutrino mass ordering: for normal ordering the global fit is consistent with CP conservation within $1σ$, whereas for inverted ordering CP-violating values of $δ_{CP}$ around $270^\circ$ are favored against CP conservation at more than $3.6σ$. While the present data has in principle $2.5$--$3σ$ sensitivity to the neutrino mass ordering, there are different tendencies in the global data that reduce the discrimination power: T2K and NOvA appearance data individually favor normal ordering, but they are more consistent with each other for inverted ordering. Conversely, the joint determination of $|Δm^2_{3\ell}|$ from global disappearance data prefers normal ordering. Altogether, the global fit including long-baseline, reactor and IceCube atmospheric data results into an almost equally good fit for both orderings. Only when the $χ^2$ table for atmospheric neutrino data from Super-Kamiokande is added to our $χ^2$, the global fit prefers normal ordering with $Δχ^2 = 6.1$. We provide also updated ranges and correlations for the effective parameters sensitive to the absolute neutrino mass from $β$-decay, neutrinoless double-beta decay, and cosmology.

Figures (13)

• Figure 1: Global $3\nu$ oscillation analysis. We show $\Delta\chi^2$ profiles minimized with respect to all undisplayed parameters. The red (blue) curves correspond to Normal (Inverted) Ordering. Solid and dashed curves correspond to the two variants of the analysis as described in the labels (notice that in the upper two panels the red-dashed and blue-solid lines almost completely overlap).
• Figure 2: Global $3\nu$ oscillation analysis. Each panel shows the two-dimensional projection of the allowed six-dimensional region after minimization with respect to the undisplayed parameters. The regions in the four lower panels are obtained from $\Delta\chi^2$ minimized with respect to the mass ordering. The different contours correspond to $1\sigma$, 90%, $2\sigma$, 99%, $3\sigma$ CL (2 dof). Colored regions (black contours) correspond to the variant with IC19 and without SK-atm (with IC24 and with SK-atm).
• Figure 3: Dependence of the global $\Delta\chi^2$ function on the Jarlskog invariant. The red (blue) curves are for NO (IO). Solid (dashed) curves are for the <<IC19 w/o SK-atm>> (<<IC24 with SK-atm>>) $\Delta\chi^2$.
• Figure 4: Predicted number of events as a function of $\delta_\text{CP}$ for the T2K (left) and NOvA (right) appearance data sets. $\sin^2\theta_{23}$ varies between 0.44 and 0.58, where the lower-light (upper-dark) bound of the colored bands corresponds to 0.44 (0.58). Red (blue) bands correspond to NO (IO). For the other oscillation parameters we have adopted $\sin^2\theta_{13} = 0.0222$, $|\Delta m^2_{3\ell}| = 2.5\times 10^{-3}~\text{eV}^2$, $\sin^2\theta_{12} = 0.32$, $\Delta m^2_{21} = 7.5\times 10^{-5}~\text{eV}^2$. The horizontal dashed lines show the observed number of events, with the $\pm 1\sigma$ statistical error indicated by the gray shaded band.
• Figure 5: $\Delta\chi^2$ profiles as a function of $\delta_\text{CP}$ for different data sets and combinations as labeled in the figure. In the curves where the reactors $R$ are not included in the combination we have fixed $\sin^2\theta_{13} = 0.0222$ as well as the solar parameters and minimized with respect to $\theta_{23}$ and $|\Delta m^2_{3\ell}|$. When the reactors are included $\theta_{13}$ is also marginalized. Left (right) panels are for IO (NO) and $\Delta\chi^2$ is shown with respect to the global best-fit point for each curve. Upper panels are for the NuFIT 5.0 data set, whereas lower panels correspond to the current update.