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Optimizing Sterile Neutrino Searches: Impact of Position Resolution in Short-Baseline Reactor Experiments

Young Ju Ko

TL;DR

This paper addresses sterile neutrino searches in very short-baseline reactor experiments by comparing segmented scintillator and opaque liquid scintillator (OLS) detectors at HANARO and Kijang. It employs a unified simulation framework with pseudo-data and oscillation templates characterized by $\Delta m^2$ and $\sin^2 2\theta$, generating up to $10^8$ events per site and using both segment-ratio and absolute $L/E$ analyses to derive 90% CL exclusions via $P=\exp(-\Delta\chi^2/2)$. The results show that OLS, with centimeter-scale position resolution, achieves leading sensitivity across a broad parameter space, while the segmented approach provides limited improvement under conservative background and reactor-power conditions. The findings highlight OLS as a promising path for resolving remaining tensions in global sterile neutrino searches, contingent on further detector validation and more detailed background modeling.

Abstract

The impact of position resolution on the sensitivity of short-baseline reactor neutrino experiments searching for light sterile neutrinos is investigated. Detailed simulations are conducted to evaluate two detector configurations: a segmented detector and an opaque liquid scintillator (OLS) detector, each positioned at two candidate research reactor sites, HANARO and Kijang. For both detector types, pseudo-data are generated under realistic assumptions regarding neutrino flux, detector response, and background levels. Oscillation analyses are performed to estimate detector sensitivity, incorporating both statistical and systematic uncertainties. The results indicate that the OLS detector, owing to its superior position resolution, achieves leading sensitivity across a wide range of oscillation parameters, even under conservative experimental conditions. These findings underscore the potential of OLS technology as a highly effective approach for future sterile neutrino searches.

Optimizing Sterile Neutrino Searches: Impact of Position Resolution in Short-Baseline Reactor Experiments

TL;DR

This paper addresses sterile neutrino searches in very short-baseline reactor experiments by comparing segmented scintillator and opaque liquid scintillator (OLS) detectors at HANARO and Kijang. It employs a unified simulation framework with pseudo-data and oscillation templates characterized by and , generating up to events per site and using both segment-ratio and absolute analyses to derive 90% CL exclusions via . The results show that OLS, with centimeter-scale position resolution, achieves leading sensitivity across a broad parameter space, while the segmented approach provides limited improvement under conservative background and reactor-power conditions. The findings highlight OLS as a promising path for resolving remaining tensions in global sterile neutrino searches, contingent on further detector validation and more detailed background modeling.

Abstract

The impact of position resolution on the sensitivity of short-baseline reactor neutrino experiments searching for light sterile neutrinos is investigated. Detailed simulations are conducted to evaluate two detector configurations: a segmented detector and an opaque liquid scintillator (OLS) detector, each positioned at two candidate research reactor sites, HANARO and Kijang. For both detector types, pseudo-data are generated under realistic assumptions regarding neutrino flux, detector response, and background levels. Oscillation analyses are performed to estimate detector sensitivity, incorporating both statistical and systematic uncertainties. The results indicate that the OLS detector, owing to its superior position resolution, achieves leading sensitivity across a wide range of oscillation parameters, even under conservative experimental conditions. These findings underscore the potential of OLS technology as a highly effective approach for future sterile neutrino searches.
Paper Structure (6 sections, 4 equations, 5 figures)

This paper contains 6 sections, 4 equations, 5 figures.

Table of Contents

  1. Introduction
  2. Estimation of Sensitivities
  3. Assumptions for Experimental Setup
  4. Sensitivity of Segmented Detector
  5. Sensitivity of Detector using Opaque LS
  6. Conclusion

Figures (5)

  • Figure 1: One-dimensional histograms of the generated pseudo-events. Left: Neutrino energy spectrum sampled according to the $^{235}$U flux model by Huber PhysRevC.84.024617 and the inverse beta decay cross-section by Vogel & Beacom and Beacom PhysRevD.60.053003. Center: Distribution of baselines for accepted events at the HANARO site, assuming a 12-meter baseline and the detector configuration described in the text. Right: Baseline distribution for the Kijang research reactor site, based on a 7-meter baseline. All distributions are based on $10^8$ generated events per site, taking into account detector geometry and spatial acceptance.
  • Figure 2: Simulated prompt energy spectra for selected detector segments. Left: Segment 1 energy distributions for the HANARO site (black) and Kijang site (red), both in the absence of oscillation. Right: Segment 2 and 4 energy spectra. Without oscillation, Segment 2 and 4 are shown in black and red, respectively. With oscillation ($\Delta m^2 = 2.4$ eV$^2$, $\sin^2 2\theta = 0.14$), Segment 2 and 4 appear in blue and magenta.
  • Figure 3: Left: The $\chi^2$ distribution as a function of the oscillation amplitude $\sin^2 2\theta$, evaluated for a fixed mass-squared difference ($\Delta m^2 = 1.02$ eV$^2$) from one pseudo-dataset under the HANARO configuration. Right: The corresponding probability density function (PDF; black) and cumulative distribution function (CDF; blue) derived from the $\chi^2$ curve. The red line indicates the 90% CL exclusion limit.
  • Figure 4: Templates of $L/E$ distributions for OLS detector simulations. The black and red lines show the no-oscillation hypothesis for HANARO and Kijang, while the blue and magenta lines correspond to an oscillation hypothesis with $\Delta m^2 = 2.4~\mathrm{eV}^2$ and $\sin^2 2\theta = 0.14$.
  • Figure 5: Comparison of detector sensitivities: segmented (black) and OLS (blue) detectors at HANARO (dashed) and Kijang (solid). Exclusion limits from Daya Bay + Bugey-3 PhysRevLett.117.151801, STEREO nature.613.257, and PROSPECT PhysRevD.103.032001 are overlaid for reference.