Enhancing Angular Sensitivity of Segmented Antineutrino Detectors for Reactor Monitoring Applications

Abstract

We present a potential improvement over the standard method developed to determine antineutrino directionality in inverse-beta-decay detectors. The previously developed method for quantifying directionality in monolithic and segmented detectors may be ambiguous in methodology. In this paper, we present a new directionality algorithm and include error analysis. We have developed a new algorithm based on a measure of ``distance'' between two matrices. We report findings for our research in reactor-antineutrino directionality, and emphasize that the algorithm has broad applications whenever one desires computationally efficient 2D pattern-matching. We treat data from detector segments in the form of a matrix. The validation of our algorithm boils down to comparing a Monte Carlo generated ``empirical'' data set to a simulated data set. The empirical data set is generated for a particular orientation of the neutrino beam. We identify an optimal segmentation scale in the low-count regime. We also discuss the shortcomings of the conventional method and how this knowledge can be applied to segmented detectors, hybrid designs, and generalized validation, agnostic to the physics of detector design.

Figures (24)

• Figure 1: To-scale diagram showing a characteristic neutron $xy$-trajectory projection from IBD vertex to capture location, as well as dimensions of segments in four 2D-segmented detectors: SANDD, MAD, Bugey, and PROSPECT. If printed on a letter/A4 format (21.6-mm-wide paper), the lines would correspond to proper size of those detector segments. This particular event if started from the center of either MAD or Prospect segment would have the capture event in the same segment as the prompt.
• Figure 2: Bugey 3 and PROSPECT directional data. For Bugey, only percentages were originally reported Cussonneau:1992lua, and only the inner-segment data is shown here. Report baselines and active reactor core sized. For Bugey, the detector was almost directly below the power reactor PhysRevD.111.032014Jayakumar:2024job. The neutrino directions are shown by the corresponding arrows.
• Figure 3: Angular uncertainty calculated using the conventional "Chooz" approach. A selected number of segmented detectors along with Chooz is highlighted. Useful IBD events are those that have prompt and delayed signals in separate segments. This result is taken from our previous study Duvall:2024cae.
• Figure 4: Diagram explaining the prompt-delayed segment geometry, as well as neutrino and axes orientation. In this work we assume that neutrino "wind" is in $xy$ plane, at an angle $\nu$ with the $x$ axis. The prompt and delayed segment in this diagram shown for illustrative purposes; the actual separation depends on the segment size --- for large segments, prompt and delayed events would happen in the same segment. It is also illustrated that capture is not necessarily aligned with the neutrino beam (only on average it is the case as discussed in this paper). To study the angular dependence we vary the angle of neutrino with respect to the detector's $x$ and $y$ axes (i.e. rotation of the detector along $z$ axis).
• Figure 5: Top: Spatial distribution ($xy$ projection) for simulated IBD neutrons: first scatters (left) and captures (right) locations, relative to the IBD vertex placed at the origin. Bottom: Polar histograms of neutron first-scatter (left) and capture (right) locations from IBD simulated in RATPAC2. These distributions are for a 10k event run with 0.1% ${}^6$Li loading. Note a clear bias toward the $+x$-direction --- the direction of incoming neutrino is along positive $x$ axis (zero angle).