An ultrafast plenoptic-camera system for high-resolution 3D particle tracking in unsegmented scintillators

TL;DR

This work introduces PLATON, a paradigm-shifting detector concept that enables ultrafast 3D imaging of events in large unsegmented scintillators by combining plenoptic cameras with time-resolving SPAD arrays. The authors demonstrate a first plenoptic camera instrumented with SPAD sensors, validate a photon-level post-processing and optical-calibration pipeline, and show event-by-event reconstruction for Sr-90 electrons as well as detailed neutrino-detection studies via simulations. Key contributions include a data-driven optical model calibration, a transformer-based reconstruction framework with density-aware losses, and detailed assessments of sub-mm to mm-scale spatial resolution across module sizes from centimetre-scale to 1 m^3. The results indicate strong potential for high-precision tracking and calorimetry in unsegmented scintillators, with broad implications for neutrino physics, double-beta decay searches, and medical imaging, while outlining practical paths to further improvements in optics, SPAD arrays, and deep-learning post-processing. The PLATON approach promises enhanced spatial and temporal resolution in dense detector volumes, enabling new event-by-event analyses and scalable detector concepts for future experiments.

Abstract

Detectors deployed in high-resolution neutrino experiments, particle calorimetry, or dark matter candidate searches require dense and massive active materials and, in some cases, extremely fine segmentation. This is essential for achieving precise three-dimensional tracking of the interaction products and enabling accurate particle-flow reconstruction. Organic scintillator detectors, for example, in the form of scintillating fibres, offer sub-millimetre spatial and sub-nanosecond temporal resolution. However, such systems introduce significant challenges in construction and demand a large number of readout electronics channels, leading to extremely high costs that are difficult to mitigate. In this article, we propose a paradigm shift in the detection of elementary particles that leads to ultrafast three-dimensional high-resolution imaging in large volumes of unsegmented scintillator. The key enabling technologies are plenoptic systems and time-resolving single-photon avalanche diode (SPAD) array imaging sensors. Together, they allow us, for the first time ever with a plenoptic camera, the reconstruction of the origin of single photons in the scintillator, thereby facilitating an event-by-event analysis. A case study focused on neutrino detection demonstrates the unique potential of this approach, achieving full event reconstruction with a spatial resolution on the order of two hundred micrometres. This work paves the way for a new class of particle scintillator-based detectors, whose capabilities should be further enhanced through future developments and expanded to Cherenkov light detection and calorimetry at collider neutrino experiments, searches for neutrinoless double beta decay, as well as applications such as medical imaging and fast neutron detection.

Figures (9)

• Figure 1: PLATON detection and reconstruction principle and the PLATON camera prototype.a The PLATON imaging principle. A plenoptic camera detects photons emitted by a charged particle transversing the scintillator. b Principle used to reconstruct single photon micro-images, using the microlens centre to determine the angle of the arriving photon. The intersection points of multiple photons are then used to reconstruct the particle track. c The PLATON camera prototype. Two insets show the ceramic MLA mount and a microscopy shot of the MLA itself. Here, the spill of the adhesive used to mount the MLA to the ceramic frame on the MLA can be seen on two sides. d The experimental setup, measuring $^{90}\text{Sr}$-electrons using the PLATON camera prototype.
• Figure 2: Position reconstruction results for a point-like light source with the PLATON prototype.a Cropped images of the data taken during the calibration measurements. Visible is the calibration point source at different depths, on the optical axis; in classical imaging, the number of micro-images is used to infer the depth of the imaged objects. b True (white circles) and reconstructed (blue crosses) positions of the back-slit point light source with respect to the PLATON prototype. Grey circles indicate the steps done by the moving stage projected onto the two perpendicular planes. The "violin" plots of the reconstructed depth (c) and lateral position (d) of the light source are shown. The dashed line corresponds to the case of a perfect reconstruction. The probability density function of the source depth or lateral position is shown for the calibration (blue) and validation (yellow) samples. The one-sided distributions of the residuals of the measured 3D positions obtained from the validation (e) and calibration (f) samples are shown. g The depth (green), 2D radial (orange), and 3D (blue) spatial resolutions as a function of the number of photons sampled from the calibration sample are shown on bottom right. The dashed horizontal lines correspond to the resolutions for high yield obtained from f.
• Figure 3: Detection of $\beta$ electrons from a $^{90}\text{Sr}$ using the PLATON prototype.a PLATON camera prototype pointing to the scintillator block exposed to the $^{90}\text{Sr}$ positioned on the top face. b A candidate electron event in the scintillator (green volume) selected from the $^{90}\text{Sr}$ sample. The prototype main lens, the reconstructed ray trace of the scintillation photons (orange lines), the nominal position of the source (red dot) and the reconstructed position of the electron (green cross) are shown. Other $^{90}$Sr events can be found in Fig. \ref{['fig:90Sr-events']}. c Distribution of the number of counts per frame for the $^{90}\text{Sr}$ (orange) and the background (blue) samples. d Residual of the reconstructed $^{90}\text{Sr}$ electron position from the $^{90}\text{Sr}$ sample with 4 counts (green), 3 counts (orange) and from background sample (blue) with 3 counts.
• Figure 4: Simulation and evaluation results of the proposed PLATON detector module.a Simulated interaction of a muon neutrino in the PLATON module. Both the truth particle tracks and the ray traces of the detected photons along with their arrival positions at the SPAD array are shown in different tones of orange. The count time distributions for signal photons (orange) and dark counts (blue) are shown in b, while c illustrates the frames collected by the SPAD array sensors. 3D spatial resolution as a function of the particle range (d) and the number of particles in the event (e). Respectively, the distribution of the particle range (d) and of the number of particles per event (e) is shown (dashed light blue).
• Figure 5: Simulated muon neutrino event analysis results.a Particle tracks reconstructed from a CC $1\mu 0\pi 2p$ neutrino interaction (a muon and two protons with no pions) after applying the image post-processing and the pattern recognition. b Residual of the reconstructed neutrino vertex position for proton events. c Difference between the number of particles produced by the neutrino interaction and the number of reconstructed clusters for muon events. The measured energy loss by a proton d and a muon e along the corresponding reconstructed track for all the events. f Proton momentum resolution (mean and 68% std) as a function of the stopping proton true momentum for selected CC $1\mu 0\pi 2p$ events (dark blue line). The true momentum distribution (light blue) of the protons from all the neutrino events is also shown. g True momentum distribution of the stopping protons of the CC $1\mu 0\pi 2p$ selected sample, including efficiency and purity. h Proton reconstruction efficiency (colour map) as a function of the stopping proton true momentum and angle after applying the CC $1\mu 0\pi 2p$ selection.