⚛️ high-energy experiments

Probing Dark Matter annihilation in the Galactic Centre with TRIDENT

This paper demonstrates that the TRIDENT neutrino telescope will surpass the thermal freeze-out benchmark for dark matter annihilation in the Galactic Centre by leveraging cascade events and accounting for a previously overlooked background of Galactic neutrinos, thereby probing untested regions of parameter space.

Original authors: Yingwei Wang, Xinhui Chu, Andrew Cheek, Iwan Morton-Blake, Qichao Chang, Gwenael Giacinti, Samy Kaci, Xin Xiang, Donglian Xu, Fuyudi Zhang

Published 2026-09-09

📖 4 min read🧠 Deep dive

CC BY 4.0

Original authors: Yingwei Wang, Xinhui Chu, Andrew Cheek, Iwan Morton-Blake, Qichao Chang, Gwenael Giacinti, Samy Kaci, Xin Xiang, Donglian Xu, Fuyudi Zhang

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

For decades, astronomers have known that the visible stars and gas in our galaxy make up only a small fraction of its total mass. The rest is an invisible substance called dark matter, which reveals itself only through its gravity, holding galaxies together and shaping the cosmos. While we cannot see it, physicists suspect that dark matter particles might occasionally collide and annihilate, vanishing in a burst of energy that produces other particles, including neutrinos. These ghostly particles zip through the universe almost entirely unimpeded, carrying a direct message from the heart of the galaxy. The challenge is that the universe is also filled with a noisy background of neutrinos created by cosmic rays crashing into gas, making it difficult to spot the faint signal of dark matter. To solve this, scientists are building massive new detectors deep underwater, hoping to catch these rare events and finally reveal the nature of the invisible universe.

A team of researchers has now simulated how a future deep-sea telescope, planned for the South China Sea, will hunt for these signals. This instrument, known as TRIDENT, is designed to be one of the largest neutrino detectors ever built, spanning several cubic kilometers of seawater. The researchers used detailed computer models to predict how well TRIDENT could spot dark matter annihilating in the center of our galaxy. Their work suggests that the telescope will be powerful enough to detect dark matter particles with masses up to one hundred thousand times that of a proton. Specifically, for a dark matter particle weighing ten trillion electron volts, the telescope could measure an annihilation rate as low as five times ten to the negative twenty-seventh cubic centimeters per second. This level of sensitivity is significant because it dips below the theoretical benchmark known as the "thermal freeze-out," a value that represents the rate at which dark matter would have naturally produced the amount we see in the universe today. If such particles exist, TRIDENT could be the first to find them.

A key discovery in this study is that the telescope's ability to find dark matter depends heavily on the type of neutrino event it records. Neutrinos interacting with water create two distinct patterns of light: long, straight tracks and compact, spherical bursts called cascades. While previous studies often focused on the tracks, which are easier to trace back to their source, this research shows that the cascades are actually more sensitive to the dark matter signal. These cascades, which come from specific types of neutrino interactions, provide a much sharper picture of the energy involved. By combining both types of events, the researchers found that the telescope's sensitivity improves dramatically, allowing it to probe regions of the universe that have remained untested.

However, the path to discovery is not without obstacles. The researchers identified a major source of confusion that had been overlooked in previous studies: a background of neutrinos produced within our own galaxy. These are created when high-energy cosmic rays collide with interstellar gas, creating a diffuse glow of neutrinos that mimics the signal scientists are looking for. The study shows that this background is particularly troublesome at high energies, above ten trillion electron volts, where it can make the telescope's sensitivity appear about half as good as it would be in a perfect, empty sky. While this background is a significant hurdle, the researchers found that the uncertainty in the shape of the dark matter cloud at the center of the galaxy remains an even larger source of doubt. Depending on how dense the dark matter is in the very center, the telescope's sensitivity could vary by a factor of ten.

To test the real-world value of these findings, the team applied their results to a specific theory of dark matter involving a new force-carrying particle. In this scenario, dark matter particles interact with each other but barely touch ordinary matter, making them invisible to traditional detectors on Earth. The simulations showed that TRIDENT would be uniquely capable of exploring this hidden territory, reaching deep into the "neutrino fog" where other experiments struggle. Unlike gamma-ray telescopes, which lose their power at these high energies, or direct detection experiments that cannot see these specific particles, the deep-sea telescope offers a complementary window. The study concludes that TRIDENT is poised to explore the most interesting and untested parts of the dark matter landscape, potentially uncovering the first evidence of these elusive particles and transforming our understanding of the universe's hidden mass.

Technical Summary: Probing Dark Matter Annihilation in the Galactic Centre with TRIDENT

Problem Statement
The nature of dark matter (DM) remains a fundamental unsolved problem in physics. While the thermal freeze-out mechanism predicts a thermally averaged annihilation cross-section of $\langle \sigma v \rangle \approx 3 \times 10^{-26} \text{ cm}^3 \text{ s}^{-1}$ for a wide range of DM masses, the region above $\sim 100$ GeV remains largely untested by indirect detection methods. High-energy $\gamma$ -ray telescopes have made progress, but neutrino telescopes offer a complementary approach, particularly for the $10^3 - 10^5$ GeV mass range. A significant challenge in searching for DM annihilation in the Galactic Centre is the presence of backgrounds, specifically the diffuse Galactic neutrino flux produced by interactions between hadronic cosmic rays and interstellar gas. This background has been overlooked in previous sensitivity studies but is expected to impact high-energy searches.

Methodology
The authors present the first model-independent sensitivity projections for the TRIDENT (TRopIcal DEep-sea Neutrino Telescope) deep-sea neutrino telescope, located in the South China Sea. The analysis utilizes the full detector design and the TRIDENTSim Monte Carlo simulation framework, which models neutrino interactions, secondary particle propagation, and Cherenkov photon detection using hybrid Digital Optical Modules (hDOMs).

The study employs a maximum-likelihood approach to evaluate sensitivity to DM annihilation into Standard Model particles ( $b\bar{b}$ , $\tau^+\tau^-$ , $\nu\bar{\nu}$ , and $4\nu$ channels). Key methodological components include:

Event Topologies: The analysis separately considers "track" events (primarily $\nu_\mu$ charged-current interactions) and "cascade" events (primarily $\nu_e, \nu_\tau$ charged-current and all-flavor neutral-current interactions).
Background Modelling: The study incorporates atmospheric neutrinos, prompt atmospheric neutrinos, and diffuse astrophysical neutrinos. Crucially, it introduces a novel treatment of the Galactic plane neutrino background, modeled using stochastic realizations of discrete PeVatron-like sources and compared against the $KRA5_\gamma$ gamma-ray constrained template.
Signal Extraction: The analysis uses Asimov datasets to determine 95% confidence level (CL) upper limits on $\langle \sigma v \rangle$ over a 10-year exposure, accounting for energy and angular resolution smearing.
Halo Uncertainties: The sensitivity is evaluated against variations in the DM density profile, comparing the benchmark NFW profile against a "bracketed" halo model that encompasses uncertainties from N-body simulations and astrometry.
Particle Model Inference: To contextualize the results, the authors apply their limits to a specific $U(1)_{L_i-L_j}$ extension of the Standard Model, which includes a $Z'$ boson and Dirac fermion DM, calculating thermal relic densities and Sommerfeld enhancements.

Key Contributions

First TRIDENT Sensitivity Projections: This work provides the first comprehensive forecast for TRIDENT's capability to probe DM annihilation in the Galactic Centre.
Superiority of Cascade Events: The analysis demonstrates that cascade events, driven by $\nu_e$ and $\nu_\tau$ , offer greater sensitivity to DM signals than track events, particularly for neutrino final states. This is attributed to the superior energy resolution of cascades ( $\sim 10\%$ vs. $\sim 80\%$ for tracks), which allows for better discrimination of spectral features (e.g., distinguishing box-shaped $4\nu$ spectra from line-like $\nu\bar{\nu}$ spectra).
Inclusion of Galactic Plane Background: The paper is the first to quantitatively evaluate the impact of Galactic plane neutrinos (from cosmic ray-gas interactions) on DM searches. The authors find this background degrades sensitivity by up to a factor of 2 at energies above $\sim 10$ TeV, where the hard Galactic spectrum becomes dominant.
Halo Profile Uncertainty Quantification: The study confirms that uncertainties in the DM density profile (specifically the difference between cuspy and cored profiles) remain the dominant source of systematic uncertainty, affecting sensitivity by approximately an order of magnitude, which is larger than the impact of the Galactic neutrino background.

Results

Sensitivity Reach: Assuming an NFW halo profile and 10 years of exposure, TRIDENT is projected to probe annihilation cross-sections down to $\langle \sigma v \rangle \approx 5 \times 10^{-27} \text{ cm}^3 \text{ s}^{-1}$ for 10 TeV DM. This falls below the canonical thermal freeze-out benchmark ( $3 \times 10^{-26} \text{ cm}^3 \text{ s}^{-1}$ ).
Channel Performance: For neutrino final states ( $\nu\bar{\nu}$ and $4\nu$ ), both track and cascade analyses are expected to reach the thermal relic value in the multi-TeV mass range. Cascade analyses generally provide tighter limits due to better energy resolution.
Background Impact: The inclusion of the stochastic Galactic plane neutrino background weakens the sensitivity limits, particularly for cascade events above 10 TeV, by a factor of approximately 2. This effect is smaller than the uncertainty introduced by the DM halo profile but is significant enough to potentially mimic a positive annihilation signal.
Model Constraints: In the context of the $U(1)_{L_\mu-L_\tau}$ model, TRIDENT is projected to probe parameter space consistent with thermal relic DM, including regions where direct detection experiments (like PandaX-4T) and $\gamma$ -ray telescopes (like H.E.S.S.) lose sensitivity. Specifically, for $m_\chi \gtrsim 600$ GeV, TRIDENT can confidently exclude the thermal relic scenario in this model, even accounting for halo uncertainties.

Significance
The paper positions TRIDENT as a leading probe for high-mass dark matter ( $10^3 - 10^5$ GeV), a regime that is currently untested and represents a critical region for the "WIMP miracle." The authors argue that the inclusion of cascade events is vital for maximizing sensitivity, guiding pre-deployment detector optimization. Furthermore, the identification of the Galactic plane neutrino background as a limiting factor at high energies highlights the need for advanced analysis techniques to distinguish between DM signals and astrophysical backgrounds. By contextualizing these limits within a specific particle physics model, the work demonstrates that TRIDENT offers unique complementarity to $\gamma$ -ray and direct detection experiments, potentially accessing parameter space (such as the "neutrino fog") that is inaccessible to other methods.

Technical Summary: Probing Dark Matter Annihilation in the Galactic Centre with TRIDENT

More like this