[Paper Review] White paper: CeLAND - Investigation of the reactor antineutrino anomaly with an intense 144Ce-144Pr antineutrino source in KamLAND

A. Gando, Y. Gando+58 more|arXiv (Cornell University)|Sep 26, 2013

Neutrino Physics Research4 citations

TL;DR

This paper proposes CeLAND, a short-baseline neutrino oscillation experiment using a 75 kCi 144Ce-144Pr antineutrino source deployed in the KamLAND detector to test the reactor antineutrino anomaly. By measuring energy and position-dependent flux suppression via inverse beta decay, CeLAND will probe sterile neutrino mixing with >95% confidence level sensitivity after 1.5 years, covering the full parameter space of the anomaly with high precision and minimal reactor-related uncertainties.

ABSTRACT

We propose to test for short baseline neutrino oscillations, implied by the recent reevaluation of the reactor antineutrino flux and by anomalous results from the gallium solar neutrino detectors. The test will consist of producing a 75 kCi 144Ce - 144Pr antineutrino source to be deployed in the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND). KamLAND's 13m diameter target volume provides a suitable environment to measure energy and position dependence of the detected neutrino flux. A characteristic oscillation pattern would be visible for a baseline of about 10 m or less, providing a very clean signal of neutrino disappearance into a yet-unknown, "sterile" state. Such a measurement will be free of any reactor-related uncertainties. After 1.5 years of data taking the Reactor Antineutrino Anomaly parameter space will be tested at > 95% C.L.

Motivation & Objective

• To test the reactor antineutrino anomaly (RAA) by searching for short-baseline electron antineutrino disappearance into a sterile neutrino state.
• To eliminate reactor-related uncertainties by using an intense, well-calibrated artificial antineutrino source instead of reactor fluxes.
• To achieve high sensitivity to sterile neutrino mixing parameters, particularly in the region with |Δm²_new| ≥ 0.1 eV².
• To improve the precision of the neutrino mixing angle θ₁₃ and assess implications for CP violation in the leptonic sector.
• To provide a definitive test of the sterile neutrino hypothesis, either confirming its existence or ruling it out with high confidence.

Proposed method

• Deploy a 75 kCi 144Ce-144Pr antineutrino source in the Kamioka Liquid Scintillator Anti-Neutrino Detector (KamLAND), exploiting the 144Ce decay (T₁/₂ = 285 days) and subsequent 144Pr decay (T₁/₂ = 17.3 min) to produce antineutrinos with Q-values up to 2.996 MeV.
• Utilize inverse beta decay (IBD) as the primary detection channel, characterized by a prompt positron signal and a delayed neutron capture on hydrogen, enabling effective background suppression.
• Position the source at 9.5 m from the detector center to achieve a baseline suitable for observing oscillation patterns in the 10 m range.
• Implement a 16 cm thick tungsten alloy shield to reduce background from beta and gamma emissions, particularly the 2.185 MeV γ-ray from 144Pr, and to ensure safe handling and transport.
• Use a dedicated calorimeter to measure the absolute activity of the 144Ce source with 1–1.5% uncertainty, crucial for rate-based analysis.
• Combine shape analysis of the energy spectrum with absolute rate measurements to enhance sensitivity to oscillation parameters.

Experimental results

Research questions

• RQ1 Can the reactor antineutrino anomaly be explained by short-baseline electron antineutrino oscillations into a sterile neutrino state?
• RQ2 What is the sensitivity of a 75 kCi 144Ce-144Pr source in KamLAND to the parameter space of the reactor antineutrino anomaly?
• RQ3 How does combining energy spectrum shape and absolute event rate measurements improve sensitivity to sterile neutrino mixing?
• RQ4 To what extent can the absolute activity calibration of the source reduce systematic uncertainties in the measurement?
• RQ5 What is the impact of this measurement on the determination of θ₁₃ and future CP violation studies in the lepton sector?

Key findings

• After 1.5 years of data taking, CeLAND will probe the majority of the reactor antineutrino anomaly parameter space with greater than 95% confidence level (C.L.) exclusion of the non-oscillation hypothesis.
• The inclusion of absolute rate information, assuming 1.5% uncertainty in source activity, significantly improves sensitivity, especially in the high Δm²_new region.
• With 6 months of data, CeLAND can already place strong limits on the region of interest, demonstrating rapid sensitivity gain.
• The experiment achieves excellent sensitivity to small mixing angles, with sin²2θ_new ∼ 0.05 excluded at 95% C.L. for large Δm²_new values.
• For Δm²_new ∼ 0.1 eV², the long baseline of 9.5 m enables high sensitivity due to the oscillation pattern's visibility in the energy spectrum.
• CeLAND’s combined shape and rate analysis sensitivity exceeds that of other proposed source experiments, making it a uniquely powerful probe of sterile neutrinos.