[Paper Review] Extending the NOvA Physics Program

M. D. Messier|arXiv (Cornell University)|Aug 1, 2013

Radiation Therapy and Dosimetry7 citations

TL;DR

This paper proposes extending the NOvA experiment's exposure through increased detector mass and running time to significantly enhance its sensitivity to three key neutrino physics questions: the nature of the ν₃ state, neutrino mass hierarchy, and CP violation. With 2× exposure, NOvA can resolve ν₃ composition for 75% of the current sin²θ₂₃ uncertainty region and establish CP violation for 45% of δ_CP values at 95% C.L., leveraging existing infrastructure at Ash River.

ABSTRACT

Following the precise measurement of $θ_{13}$ by reactor experiments three main questions remain within the now standard picture of neutrino oscillations: (1) Is the value of $θ_{23}$ such that the $ν_3$ state contains more muon flavor, more tau flavor, or equal amounts? (2) What is the neutrino mass hierarchy? (3) Is CP violated in the neutrino sector? The NOvA experiment will address all three of these questions. In each case the measurements are statistics limited motivating exploration of what could be accomplished with additional exposure.

Motivation & Objective

• To assess the impact of increased exposure on NOvA’s ability to resolve the nature of ν₃ in terms of its muon and tau flavor components.
• To evaluate how extended exposure improves sensitivity to the neutrino mass hierarchy.
• To determine the reach for establishing CP violation in the neutrino sector as a function of exposure.
• To explore cost-effective, low-risk extensions of the NOvA program using existing beam, site, and detector infrastructure.
• To propose a two-phase strategy: first, doubling exposure via detector mass and runtime; second, adding a 5 kt liquid argon TPC for further enhancement.

Proposed method

• Uses simulated neutrino oscillation data to project NOvA’s sensitivity to ν₃ composition, mass hierarchy, and CP violation as a function of exposure.
• Applies statistical criteria (95% C.L. for ν₃ composition, >2 and >3 σ C.L. for mass hierarchy, 95% C.L. for CP violation) to evaluate reach.
• Models exposure extension via two paths: increasing detector mass to 18 kt and extending run time to 10 years (2× baseline), or adding a 5 kt liquid argon TPC (4× effective exposure).
• Relies on the existing NuMI beam (700 kW), Ash River site, and NOvA production factories to minimize additional costs and risks.
• Quantifies physics reach using percent coverage of sin²θ₂₃ and δ_CP parameter space at specified confidence levels.
• Uses the baseline exposure (14 kt, 700 kW, 6 years) as reference, with 2× and 4× exposure scenarios for comparison.

Experimental results

Research questions

• RQ1 What fraction of the current sin²θ₂₃ uncertainty region can NOvA resolve for ν₃ composition with 2× and 4× exposure?
• RQ2 How does increased exposure improve NOvA’s sensitivity to the neutrino mass hierarchy across the δ_CP parameter space?
• RQ3 For what fraction of δ_CP values can CP violation be established at 95% C.L. with baseline, 2×, and 4× exposure?
• RQ4 What is the cost and feasibility of extending NOvA’s exposure using existing infrastructure?
• RQ5 Can a 5 kt liquid argon TPC at Ash River significantly enhance NOvA’s physics reach in a second phase?

Key findings

• With 2× exposure, NOvA can resolve the relative sizes of |⟨ν₃|ν_μ⟩|² and |⟨ν₃|ν_τ⟩|² at 95% C.L. for 75% of the current sin²θ₂₃ uncertainty region, up from 64% at baseline.
• With 4× exposure, this coverage increases to 80% of the allowed sin²θ₂₃ region at 95% C.L.
• For mass hierarchy resolution, 2× exposure achieves >3 σ C.L. coverage over a significant portion of the δ_CP parameter space, improving on baseline performance.
• CP violation can be established at 95% C.L. for 20% of δ_CP values with 2× exposure, increasing to 45% with 4× exposure.
• A 5 kt liquid argon TPC at Ash River would effectively increase NOvA’s exposure by a factor of 4, offering a major physics boost in a second phase.
• Extending exposure via detector mass and runtime is low-risk and cost-effective, with estimated costs of $6M/kt (or $9M/kt if construction restarts), leveraging existing infrastructure.