[Paper Review] What we (would like to) know about the neutrino mass

G. L. Fogli, E. Lisi+3 more|ArXiv.org|Sep 17, 2008

Neutrino Physics Research5 references44 citations

TL;DR

This paper presents updated global analyses of neutrino oscillation parameters, highlighting a 1.6σ preference for a non-zero mixing angle θ₁₃, with sin²θ₁₃ ≈ 0.016 ± 0.010, based on combined solar and KamLAND data. It further addresses theoretical uncertainties in neutrinoless double beta decay by introducing a constrained QRPA approach using three independent lifetime measurements to reduce nuclear matrix element uncertainties.

ABSTRACT

We present updated values for the mass-mixing parameters relevant to neutrino oscillations, with particular attention to emerging hints in favor of theta_13>0. We also discuss the status of absolute neutrino mass observables, and a possible approach to constrain theoretical uncertainties in neutrinoless double beta decay. Desiderata for all these issues are also briefly mentioned.

Motivation & Objective

• To update the global analysis of three-neutrino oscillation parameters using latest data from solar, reactor (KamLAND), and atmospheric neutrino experiments.
• To assess the status of absolute neutrino mass observables, particularly in neutrinoless double beta decay (0ν2β) and cosmological constraints.
• To reduce theoretical uncertainties in nuclear matrix elements (NMEs) for 0ν2β decay through a constrained parameter space approach.
• To evaluate the consistency of the Heidelberg-Moscow 0ν2β claim with cosmological bounds on the effective Majorana mass.
• To identify key desiderata for future experiments to resolve current tensions and confirm neutrino mass scale.

Proposed method

• Performs a global χ² analysis of neutrino oscillation data, including solar (SNO-III), KamLAND, atmospheric, long-baseline accelerator, and reactor (CHOOZ) experiments.
• Uses the survival probability Pₑₑ(θ₁₂, θ₁₃) with different functional forms in solar vs. reactor experiments to probe θ₁₃ dependence.
• Applies a constrained QRPA model for 0ν2β decay by fixing two parameters (gₚₚ, gₐ) using three independent lifetime measurements: 2ν2β, electron capture (EC), and β⁻ decay.
• Employs overconstrained parameter space in ¹⁰⁰Mo and ¹¹⁶Cd to verify predictions against experimental data, reducing NME uncertainties.
• Compares predicted effective Majorana mass mββ with cosmological bounds on Σ from CMB and Lyα forest data.
• Uses 1σ and 2σ confidence intervals from χ² marginalization to derive allowed ranges for oscillation parameters and mass observables.

Experimental results

Research questions

• RQ1 What is the current global evidence for a non-zero θ₁₃ mixing angle, and how does it evolve with new solar and reactor data?
• RQ2 Can the Heidelberg-Moscow 0ν2β signal in ⁷⁶Ge be reconciled with cosmological bounds on the effective Majorana mass?
• RQ3 To what extent can theoretical uncertainties in nuclear matrix elements for 0ν2β decay be reduced using multiple experimental constraints?
• RQ4 What is the consistency of the 0ν2β decay signal with independent data on β⁻ decay, electron capture, and 2ν2β decay in ¹⁰⁰Mo and ¹¹⁶Cd?
• RQ5 What are the implications of current data for the absolute neutrino mass scale, and what future measurements are needed to resolve tensions?

Key findings

• A 1.6σ preference for θ₁₃ > 0 emerges from combined solar and KamLAND data, with sin²θ₁₃ ≈ 0.016 ± 0.010.
• The 2008 global analysis yields best-fit values: δm² = 7.67 × 10⁻⁵ eV², sin²θ₁₂ = 0.312, sin²θ₁₃ = 0.016, sin²θ₂₃ = 0.466, Δm² = 2.39 × 10⁻³ eV².
• At 2σ confidence level, sin²θ₁₃ < 0.036, and the 3σ range extends to sin²θ₁₃ < 0.046.
• The constrained QRPA approach using β⁻, EC, and 2ν2β lifetimes in ¹⁰⁰Mo and ¹¹⁶Cd reduces NME uncertainties by overconstraining (gₚₚ, gₐ) parameters.
• The Heidelberg-Moscow 0ν2β claim implies mββ ≈ 0.11–0.36 eV, which contradicts the cosmological bound mββ < 0.08 eV unless data selection or interpretation is revised.
• A coherent assessment of the neutrino mass scale requires converging evidence from at least two of the three observables: mβ, mββ, and Σ.