TRIDENT Detector: Deep-Sea Neutrino Telescope

• TRIDENT Detector is a state-of-the-art deep-sea neutrino telescope employing hybrid digital optical modules (hDOMs) for sub-degree angular resolution and flavor identification.
• It uses an asymmetric Penrose tiling array layout and optimized PMT configurations to maximize detection efficiency while reducing power consumption and cost.
• Advanced calibration methods and deep-learning reconstruction techniques enable precise measurement of neutrino events, including rare astrophysical sources and BSM processes.

The TRIDENT Detector is a next-generation, multi-cubic-kilometer deep-sea neutrino telescope conceived for deployment in the western Pacific Ocean. Designed to discover astrophysical neutrino sources and probe all-flavor neutrino physics, TRIDENT employs advanced hybrid Digital Optical Modules (hDOMs) that integrate small, high-quantum-efficiency photomultiplier tubes (PMTs) and silicon photomultipliers (SiPMs). The detector leverages the unique optical properties of deep-sea water—characterized by long scattering lengths and moderate absorption lengths—to reach sub-degree angular resolution, delivering enhanced pointing and flavor identification capabilities compared to prior instruments.

1. Scientific Motivation and Design Principles

The primary scientific drivers for TRIDENT are the high-precision detection of astrophysical neutrino sources, resolution of the diffuse neutrino flux, measurement of neutrino flavor composition over astronomical baselines, and sensitivity to physics beyond the Standard Model. The instrumented volume is approximately 7.5 km³, composed of 1,211 vertical strings, each hosting 20 hDOMs, achieving nearly full-sky coverage due to its equatorial location (Ye et al., 2022).

Crucial design elements optimized through simulation include:

• Optical Module Configuration: The hDOMs combine multiple (e.g., 19 or 31) small PMTs with large-area SiPM arrays. The PMT choice is dictated by tradeoffs between quantum efficiency (QE), transit time spread (TTS), channel count, and cost (Shao et al., 14 Jul 2025).
• Array Layout: Modules are arranged in an asymmetric Penrose tiling pattern with 70 m and 110 m inter-string spacings to maximize instrumented volume without regular gaps, facilitate access for maintenance robots, and ensure adequate granularity for photon propagation in water.
• Seawater Optical Properties: Measurements during the TRIDENT Pathfinder (T-REX) campaign found absorption and scattering lengths of λ₍abs₎ ≃ 27 m and λ₍sca₎ ≃ 63 m at 3475 m depth (Ye et al., 2022, Zhang et al., 2023).

2. Optical Module Optimization and Instrumentation

TRIDENT's hybrid digital optical modules have been the focus of extensive cost-performance optimization (Shao et al., 14 Jul 2025):

PMT Configuration	Channel Count per hDOM	PMT Diameter (inches)	Quantum Efficiency	Typical TTS (ns)	Key Advantages
3'' PMT Array	31	3	High (R14374)	~1.4	Established performance, high QE
4'' PMT Array	19	4	Low (N2041) / High (future)	2.7 / ~1.4	Fewer channels, cost/power reduction

Performance simulations with site-specific optical backgrounds show that 19 high-QE 4'' PMTs per module provide equal or better detection efficiency and angular resolution than the 31 × 3'' PMT baseline, with about 40% fewer channels. This provides considerable reductions in power consumption, mechanical integration complexity, and cost, without sacrificing directional or double-pulse (tau flavor) identification efficiency (Shao et al., 14 Jul 2025).

Each hDOM is engineered for rugged deep-sea operation, integrating:

• Pressure-resistant glass housing,
• High-voltage bases and low-noise, low-power ASIC front-end electronics for time and waveform digitization (<7 mW/channel, SPTR ≈ 260 ps FWHM),
• FPGA-based time-to-digital converters synchronized to the White Rabbit (WR) global clock network, offering sub-nanosecond time synchronization (Wang et al., 2023, Zhang et al., 1 Jul 2025, Wang et al., 5 Feb 2025).

3. Oceanographic Site Characterization and Calibration

The South China Sea site was characterized with the T-REX pathfinder, deploying three instrumented modules in a 100-meter string at 3420 m. In situ measurements established:

• Water absorption length (λ₍abs₎ ≈ 27 m) and scattering length (λ₍sca₎ ≈ 63 m) at blue wavelengths,
• Sub-10 cm/s currents at depth, and very low biological activity and background radioactivity (Ye et al., 2022, Francener et al., 6 Nov 2024).

Calibration techniques are built into the array infrastructure:

• LED-based pulsed and steady light sources, producing isotropic emission for photon time-of-flight and spatial uniformity measurement, synchronized via the WR system to <1 ns precision (Li et al., 2023).
• PMT and CMOS camera systems in receiver modules for independent and cross-calibrated measurement of photon arrival statistics and spatial light distributions, enabling real-time determination of optical attenuation, absorption, and scattering—critical for precise event energy/vertex and directional reconstruction (Zhang et al., 2023, Tian et al., 26 Jul 2024).

Calibration signals are analyzed using methods such as:

$I(L) = I_0 \cdot \exp(-L/\lambda_{\text{att}})$

$$\lambda_{\text{att}} = -\frac{L_A-L_B}{\ln[(I_A/I_B)\cdot(I_0'/I_0)]}$$

$$N(L) = N_0\frac{dS}{4\pi L^2}\exp[-\langle L \rangle/\lambda_{\mathrm{abs}}]$$

where $I(L)$ is the detected intensity at distance $L$, $N(L)$ measured photon counts, and $dS$ is the receiver area.

4. Readout Electronics, Timing, and Data Acquisition

The detector’s performance is underpinned by high-speed, low-power ASIC-based signal conditioning, sampling, and digitization:

• Waveform Digitization: PMT signals shaped for 125 MS/s ADC sampling (16-bit), enabling charge calibration and single photoelectron (SPE) measurement up to 240 PEs (Zhang et al., 1 Jul 2025).
• Time Digitization: FPGA TDCs (delay-line plus coarse counter) provide sub-nanosecond timestamping, crucial for reconstructing Cherenkov photon arrival times over $\sim$1–100 meters (Zhang et al., 1 Jul 2025).
• Data Synchronization: White Rabbit delivers a reference clock and pulse-per-second signals, yielding synchronization skew <11 ps over 40 m—a key factor in achieving ≤0.1° angular resolution at $\gg$10 TeV (Wang et al., 2023).

The fully integrated all-data-to-shore DAQ platform supports real-time trigger distribution, control, and scalable bandwidth for large arrays.

5. Event Reconstruction and Analysis

Neutrino event reconstruction employs advanced graph neural network (GNN) techniques, which process the hDOM graph structure (nodes: modules, edges: k-nearest neighbors) and event-level/global features (Mo et al., 27 Jan 2024):

• Shower-like (νₑ CC) events: GNNs using EdgeConv blocks and photon arrival-time histograms achieve a median angular reconstruction error of 1.3° at 100 TeV, notably outperforming traditional likelihood approaches (1.7°).
• Track-like (ν_μ CC) events: GNN-based methods reach sub-0.1° angular error at high energies, matching the detector’s physical limits.

Iterative EdgeConv updates, summarized as

$$e_{ij} = \phi_\theta(u, x_i, x_j - x_i), \quad x_i' = \max_j \{e_{ij}\} + x_i, \quad u' = \Phi_\Theta(u, \text{GlobalAvg}(\{x_i'\}))$$

enable use of fine-grained timing and spatial signatures from the hDOM array to reconstruct both direction and, when possible, energy and flavor. The multi-PMT/SiPM configuration is essential for double-pulse separation (ν_τ flavor identification).

6. Complementarity, Probing Rare Processes, and Broader Impact

TRIDENT’s technical characteristics enable measurement of rare Standard Model and beyond-the-Standard-Model processes, including:

• Neutrino trident production: The array provides the spatial, timing, and particle identification resolution to isolate leptonic trident signatures in both coherent and diffractive regimes, offering sensitivity to electroweak physics and possible BSM couplings (including L_μ–L_τ Z′ bosons) (Magill et al., 2016, Francener et al., 6 Nov 2024, Francener et al., 19 Jun 2024).
• Astrophysical source discovery: Simulations predict a 5σ observation of the IceCube steady source NGC 1068 within a single year, leveraging the full-sky, equatorial coverage (Ye et al., 2022).
• Muon background measurements and calibration: Integrated muon detectors (e.g., MuonSLab) inform atmospheric muon flux models at depth, supporting background rejection and trigger optimization (Wu et al., 29 Jan 2025).

When compared to other large neutrino telescopes (e.g., IceCube, KM3NeT, Baikal-GVD), TRIDENT’s hybrid detection concept and its deployment in optically favorable waters grant superior source localization over a broader sky, essential for next-generation neutrino astronomy and cosmic ray studies.

7. Scalability, Cost, and Future Developments

Optimization studies demonstrate that a 4-inch high-QE PMT-based hDOM design maintains or enhances performance relative to the 3-inch PMT baseline, while reducing the number of channels, required power, and associated mechanical complexity by approximately 40% (Shao et al., 14 Jul 2025). The hybrid DOM architecture is thus a scalable and cost-effective solution for instrumenting >1000 strings over multi-kilometer baselines.

These findings influence not only the choice and procurement of optical sensors but also the design of ASICs, readout electronics, and DAQ infrastructure, ensuring that TRIDENT meets the demands of a competitive, next-generation, high-volume neutrino experiment in the deep sea.

---

In sum, the TRIDENT Detector concept integrates advanced hybrid photodetector arrays, precise readout and timing synchronization, rigorous optical calibration, and deep-learning–based event reconstruction within a deep-sea platform. The experiment’s design, validated through test deployments and simulation studies, is engineered for high-efficiency neutrino detection, precise flavor and directional reconstruction, and robust calibration in a dynamic marine environment. It is positioned to play a leading role in both precision neutrino physics and the broader field of multi-messenger astrophysics.