2020 Global reassessment of the neutrino oscillation picture (2006.11237v2)

Abstract: We present an updated global fit of neutrino oscillation data in the simplest three-neutrino framework. In the present study we include up-to-date analyses from a number of experiments. Concerning the atmospheric and solar sectors, we give updated analyses of DeepCore and SNO data, respectively. We have also included the latest electron antineutrino data collected by the Daya Bay and RENO reactor experiments, and the long-baseline T2K and NO$\nu$A measurements. These new analyses result in more accurate measurements of $\theta_{13}$, $\theta_{12}$, $\Delta m_{21}^2$ and $|\Delta m_{31}^2|$. The best fit value for the atmospheric angle $\theta_{23}$ lies in the second octant, but first octant solutions remain allowed at $\sim2.4\sigma$. Regarding CP violation measurements, the preferred value of $\delta$ we obtain is 1.08$\pi$ (1.58$\pi$) for normal (inverted) neutrino mass ordering. The global analysis prefers normal neutrino mass ordering with 2.5$\sigma$. This preference is milder than the one found in previous global analyses. The new results should be regarded as robust due to the agreement found between our Bayesian and frequentist approaches. Taking into account only oscillation data, there is a weak/moderate preference for the normal neutrino mass ordering of $2.00\sigma$. While adding neutrinoless double beta decay from the latest Gerda, CUORE and KamLAND-Zen results barely modifies this picture, cosmological measurements raise the preference to $2.68\sigma$ within a conservative approach. A more aggressive data set combination of cosmological observations leads to a similar preference, namely $2.70\sigma$. This very same cosmological data set provides $2\sigma$ upper limits on the total neutrino mass corresponding to $\sum\nu<0.12$ ($0.15$)~eV for normal (inverted) neutrino mass ordering.

• The paper achieves refined measurements of oscillation parameters, notably for θ23 and the CP violation phase, enhancing our understanding of neutrino behavior.
• The analysis synthesizes data from experiments like IceCube, Daya Bay, T2K, and NOvA to support a mild yet consistent preference for normal neutrino mass ordering.
• It constrains total neutrino mass by integrating results from neutrinoless double beta decay and cosmological observations, guiding future research directions.

Overview of the 2020 Global Reassessment of the Neutrino Oscillation Picture

The paper "2020 Global Reassessment of the Neutrino Oscillation Picture" conducts a comprehensive analysis of the most current neutrino oscillation data, framed within the three-neutrino model. The authors have meticulously incorporated updated datasets from diverse neutrino experiments to reassess the parameters governing neutrino oscillations. The primary focus is on improving the precision of key oscillation parameters and evaluating the implications for neutrino mass ordering, using both frequentist and Bayesian approaches.

Key Results and Methodology

The paper includes fresh analyses from a variety of experiments, such as IceCube DeepCore for atmospheric neutrinos and Sudbury Neutrino Observatory data for solar neutrinos. It also integrates recent measurements from reactor experiments like Daya Bay and RENO, and long-baseline experiments such as T2K and NOvA.

1. Oscillation Parameters:
   • The analysis achieves refined measurements of $\theta_{13}$, $\theta_{12}$, $\Delta m_{21}^2$, and $|\Delta m_{31}^2|$. The best fit for $\theta_{23}$ is noted to be in the second octant, although first octant solutions are marginally permissible.
   • For the CP violation phase ($\delta$), the preferred values are 1.08$\pi$ for normal ordering and 1.58$\pi$ for inverted ordering.
2. Mass Ordering:
   • A preference for normal neutrino mass ordering emerges, albeit with a milder 2.5$\sigma$ statistical significance compared to prior analyses. The research synthesizes findings from different experimental contexts to bolster this preference.
3. Neutrino Mass Constraints:
   • Incorporating data from neutrinoless double beta decay experiments (like Gerda, CUORE, and KamLAND-Zen) and constraints from cosmological observations, the paper provides stringent upper limits on the total neutrino mass. These cosmological datasets push the preference for normal mass ordering to a higher confidence level.

Implications and Speculation

The implications of this updated analysis are significant both for our theoretical understanding and for the design and focus of future experimental endeavors:

• Practical Implications: The improved precision in oscillation parameters helps refine theoretical models of neutrino behavior and guide new experimental setups. For instance, the sustained preference for normal mass ordering can influence the configuration of upcoming long-baseline neutrino experiments and the prioritization of future research funding.
• Theoretical Implications: The results prompt further exploration of non-standard neutrino interactions and the role of CP violation in leptogenesis. These insights may offer pathways to resolving major questions about the early universe and the matter-antimatter asymmetry.
• Future Speculations: As experimental techniques advance, we anticipate more stringent tests of the CP violation phase and potentially resolving the octant ambiguity for $\theta_{23}$. Enhanced accuracy in these parameters could unveil new physics beyond the Standard Model and further illuminate the nature of neutrino mass ordering.

In conclusion, the paper provides a robust update to the global neutrino oscillation picture, integrating multi-faceted data sources and methodologies. The approach adopted by the authors exemplifies the synergy of theoretical modeling and experimental data in contemporary particle physics, pushing the boundaries of our understanding of fundamental particles.