The fate of hints: updated global analysis of three-flavor neutrino oscillations (2007.14792v1)

Abstract: Our herein described combined analysis of the latest neutrino oscillation data presented at the Neutrino2020 conference shows that previous hints for the neutrino mass ordering have significantly decreased, and normal ordering (NO) is favored only at the $1.6\sigma$ level. Combined with the $\chi^2$ map provided by Super-Kamiokande for their atmospheric neutrino data analysis the hint for NO is at $2.7\sigma$. The CP conserving value $\delta_\text{CP} = 180^\circ$ is within $0.6\sigma$ of the global best fit point. Only if we restrict to inverted mass ordering, CP violation is favored at the $\sim 3\sigma$ level. We discuss the origin of these results - which are driven by the new data from the T2K and NOvA long-baseline experiments -, and the relevance of the LBL-reactor oscillation frequency complementarity. The previous $2.2\sigma$ tension in $\Delta m^2_{21}$ preferred by KamLAND and solar experiments is also reduced to the $1.1\sigma$ level after the inclusion of the latest Super-Kamiokande solar neutrino results. Finally we present updated allowed ranges for the oscillation parameters and for the leptonic Jarlskog determinant from the global analysis.

• The paper reveals a reduced statistical preference for normal mass ordering, with significance dropping to 1.6σ (2.7σ when combined with additional data).
• The analysis shows that the CP conserving value (180°) nearly matches the best-fit point, though CP violation hints appear at around 3σ in the inverted ordering scenario.
• The study highlights how complementary results from T2K, NOvA, LBL, and reactor experiments refine oscillation parameters and resolve previous experimental tensions.

Insights on the Updated Global Analysis of Three-Flavor Neutrino Oscillations

The paper "The fate of hints: updated global analysis of three-flavor neutrino oscillations" presents a comprehensive analysis of the current status of neutrino oscillation parameters using data from several recent neutrino experiments. This analysis reassesses the global fit of these parameters, particularly scrutinizing the hints around the neutrino mass ordering and CP violation. The researchers concentrate on deciphering newly released data, specifically those presented at the Neutrino2020 conference, while merging them with prior experimental results.

Main Findings and Numerical Results

1. Neutrino Mass Ordering: The report shows that previous indications of a preference for normal ordering (NO) have notably waned. The statistical significance for NO has dwindled to $1.6\sigma$ with the new data, although when combined with Super-Kamiokande atmospheric neutrino data, it slightly strengthens to $2.7\sigma$. This implies a reduction of previous confidence levels, suggesting that both mass orderings are increasingly comparable in their ability to explain the data.
2. CP Phase Sensitivity: The paper finds the CP conserving value ($CP = 180^\circ$) marginally aligned with the global best-fit point within $0.6\sigma$. This suggests a weakening in evidence for CP violation unless considering the inverted mass ordering (IO), where CP violation appears favored at roughly $3\sigma$. Such insights stress the need for further experimental data to improve the precision of CP phase determination.
3. T2K and NOvA Contributions: The influence of the T2K and NOvA experiments is pivotal in this updated analysis. Their results are particularly impactful on the neutrino mass ordering assessment, with the combined results displaying a high degree of statistical compatibility, despite differing tendencies regarding CP phase preferences.
4. LBL and Reactor Oscillation Complementarity: Data from long-baseline (LBL) experiments and reactor neutrino experiments provide crucial complementarity in oscillation frequency measurements, especially affecting sensitivity to the mass ordering. The integration of results from both domains strengthens constraints on the mass ordering when both analyses point toward normal ordering, though not significantly enough to discharge IO entirely.
5. Resolution of Past Tensions: Regarding the $_{21}$ parameter, the inclusion of updated sensory data from Super-Kamiokande has diminished previous discordances between KamLAND and solar neutrino investigations, reducing experimentally observed tension to $1.1\sigma$.

Implications and Future Directions

The implications of these results are twofold. Practically, finer-tuned experiments like DUNE and Hyper-Kamiokande stand to provide further clarity on mass ordering and CP violation in the coming years. Theoretically, these findings push the frontier in neutrino physics, justifying more sophisticated models that encompass the neutrino sector dynamics. Moreover, the prospective alignment or divergence of new results will be instrumental in verifying current model predictions.

Future developments will likely involve an escalation in data precision, particularly from experiments capable of stringent constraints on $_{3\ell}$ and $CP$. Advancement in detector technologies and increased exposure in long-baseline neutrino facilities will bolster observational capabilities, potentially transforming current "hints" into significant discoveries. Additionally, ongoing theoretical advancements will strive to encompass observed neutrino phenomena, increasingly mandated by the narrowing of parameter spaces verified by experiment.

In conclusion, this updated analysis offers a tempered yet informative perspective on the ongoing endeavor to pin down neutrino oscillation parameters critically, now armed with 2020's fresh experimental signals and confrontations. It sets the stage and establishes a necessary impetus for forthcoming data-enhanced undertakings to authentically identify or refute conjectures surrounding neutrino properties and behaviors in this elusively transformative sector of particle physics.