[Paper Review] Interference effects in reactor antineutrino oscillations

Zhi‐zhong Xing|arXiv (Cornell University)|Aug 7, 2018

Neutrino Physics Research5 references3 citations

TL;DR

This paper proposes a reformulated expression for reactor antineutrino oscillation probabilities that isolates a key interference term proportional to sin(Δm²₂₁L/4E) and sin[(Δm²₃₁ + Δm²₃₂)L/4E), making the dependence on neutrino mass ordering explicitly transparent. The formulation enhances sensitivity to mass ordering in experiments like JUNO and identifies a new interference term involving a light sterile neutrino, which could affect oscillation measurements if such particles exist.

ABSTRACT

We reformulate the probabilities of disappearance neutrino or antineutrino oscillations so as to single out the interference term proportional to the product of \sin[Δm^2_{21} L/(4 E)] and \sin[(Δm^2_{31} + Δm^2_{32}) L/(4 E)], which is transparently sensitive to the neutrino mass ordering. We elaborate this issue for a reactor-based antineutrino oscillation experiment like JUNO, and take account of terrestrial matter effects. If a light sterile neutrino species contributes to P(\overlineν_e o \overlineν_e), we find that there will be a new interference term proportional to the product of \sin^2 2θ_{14}, \sin[Δm^2_{21} L/(4 E)] and \sin[(Δm^2_{41} + Δm^2_{42}) L/ (4 E)] in the standard parametrization of the (3+1) X (3+1) active-sterile neutrino mixing matrix.

Motivation & Objective

• To improve the analytical transparency of interference effects in reactor antineutrino oscillations, particularly those sensitive to neutrino mass ordering.
• To identify the optimal parametrization of oscillation probabilities that isolates the interference term most directly linked to the sign of Δm²₃₁ and Δm²₃₂.
• To extend the analysis to the (3+1) neutrino mixing scheme, including the potential impact of a light sterile neutrino on oscillation interference.
• To clarify how terrestrial matter effects and detector energy resolution influence the detectability of mass ordering through interference.

Proposed method

• Reformulate the standard three-flavor oscillation probability P(ν̄ₑ → ν̄ₑ) by expressing it in terms of Δm²₂₁ and (Δm²₃₁ + Δm²₃₂), emphasizing the interference term involving their product of sine functions.
• Use the identity Δm²₂₁ = Δm²₃₁ - Δm²₃₂ to show that the interference term depends on the sum (Δm²₃₁ + Δm²₃₂), which is directly related to the neutrino mass ordering.
• Apply the same parametrization to the (3+1) active-sterile mixing framework, deriving a new interference term proportional to sin²2θ₁₄, sin(Δm²₂₁L/4E), and sin[(Δm²₄₁ + Δm²₄₂)L/4E).
• Analyze the impact of terrestrial matter effects on the oscillation probability, particularly in medium-baseline experiments like JUNO.
• Compare the proposed parametrization with existing formulations to demonstrate its analytical advantages in revealing mass ordering sensitivity.
• Use the Jarlskog invariant and CP-violating phase structure to contextualize the role of interference in CP-violating processes.

Experimental results

Research questions

• RQ1 Why is the interference term involving sin(Δm²₂₁L/4E) and sin[(Δm²₃₁ + Δm²₃₂)L/4E) more transparent for probing neutrino mass ordering than other parametrizations?
• RQ2 How does the inclusion of a light sterile neutrino modify the interference structure in reactor antineutrino oscillations?
• RQ3 What is the analytical advantage of using (Δm²₃₁ + Δm²₃₂) instead of Δm²₃₁ or Δm²₃₂ individually in the oscillation probability?
• RQ4 Can the new interference term in the (3+1) scheme be distinguished from the standard one in future experiments like JUNO?
• RQ5 How do matter effects in the Earth's crust influence the visibility of the interference term sensitive to mass ordering?

Key findings

• The interference term proportional to sin(Δm²₂₁L/4E) and sin[(Δm²₃₁ + Δm²₃₂)L/4E) is explicitly sensitive to the sign of Δm²₃₁ and Δm²₃₂, making it a direct probe of neutrino mass ordering.
• The parametrization using Δm²₂₁ and (Δm²₃₁ + Δm²₃₂) is shown to be superior for revealing mass ordering effects, especially in medium-baseline experiments like JUNO.
• In the (3+1) active-sterile neutrino mixing scheme, a new interference term emerges that is proportional to sin²2θ₁₄, sin(Δm²₂₁L/4E), and sin[(Δm²₄₁ + Δm²₄₂)L/4E), which could contaminate the standard mass ordering signal.
• The presence of such a sterile-induced interference term depends on the allowed parameter space of θ₁₄ and Δm²₄₁, Δm²₄₂, which are constrained by existing experimental data.
• The proposed parametrization maintains consistency with known results in the three-flavor case and provides a clearer analytical framework for future precision measurements.
• The method is extendable to appearance-type oscillations and can be adapted to include matter effects, though Majorana-type oscillations remain experimentally inaccessible due to mass suppression.