Semi-visible Jets from Sneaky Dark Matter
This paper proposes and evaluates a new approach for generating semi-visible jet signatures in non-resonant dark matter production, introduces an optimized matrix element to parton shower matching configuration, and establishes collider limits on the scenario through a reinterpretation of ATLAS t-channel search data.
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
Deep within the standard model of particle physics, the theory that describes how the universe is built, there is a persistent mystery: what is dark matter? While we know it exists because of its gravitational pull on galaxies, it remains invisible to our detectors, refusing to interact with light or ordinary matter. Physicists have long suspected that dark matter might not be a single, lonely particle, but rather part of a hidden sector—a parallel world with its own forces and particles that interact with our own only very weakly. In this hidden realm, there could be a force similar to the one that binds quarks together inside protons, creating a complex zoo of new particles. Some of these new particles might be stable and invisible, while others could decay into the ordinary particles we can see. When such a hidden sector is produced in a particle collider, it could create a unique signature known as a "semi-visible jet." This is a spray of particles that looks like a normal jet of debris from a high-speed collision, but with a twist: a portion of the spray vanishes into the dark sector, carrying away energy that the detector cannot see.
The search for these semi-visible jets is a critical part of the hunt for new physics at the Large Hadron Collider. However, simulating these events on a computer is notoriously difficult. The software used to predict how particles behave after a collision has evolved, and older methods of calculation are no longer compatible with the latest, more precise versions of the simulation tools. This creates a bottleneck: researchers have a powerful new way to model the hidden sector, but they need to be sure it produces the same physical results as the older, established methods before they can trust it to guide future experiments. This is the precise challenge addressed by a team of physicists who set out to compare two different mathematical models used to generate these elusive signals.
The researchers focused on two specific ways to describe how a hidden sector particle might be created in a collision. The first approach, which has been used in previous searches, relies on a large family of twenty-four different mediator particles. Each of these mediators acts as a bridge, connecting a specific type of ordinary quark to a specific type of dark quark. The second approach, which the team proposes as a more modern alternative, uses a single, versatile mediator that can connect to many different types of quarks at once. This newer model, known as the "sneaky dark matter" scenario, was designed to work seamlessly with the latest simulation software, but it had never been rigorously tested against the older method to see if they told the same story.
To settle the question, the team ran extensive computer simulations, generating millions of hypothetical collision events for both models. They carefully adjusted the settings so that the overall rate of production was comparable, allowing them to isolate the differences in how the particles behaved. At the most basic level, looking at the particles immediately after the collision but before they interact with anything else, the two models produced nearly identical results. The energy and direction of the particles were the same, suggesting that the fundamental physics of the collision was being captured correctly by both approaches.
However, as the simulation progressed to the stage where particles decay and form the final sprays of debris that a detector would actually see, subtle but important differences emerged. In the older model, the twenty-four mediator particles were very narrow and precise, leading to a distinct "bump" in the energy distribution of the resulting jets. It was as if the particles were being launched with a very specific, uniform speed. In the newer model, the single mediator had a much broader range of possible behaviors, which smoothed out this bump, resulting in a more spread-out distribution of energy. Despite this difference, the researchers found that the overall shape of the signals remained very similar. The newer model did not produce a signal so different that it would confuse the search strategies currently used by experimentalists.
A significant portion of the work involved improving the technical machinery used to generate these events. The team demonstrated that a more modern and efficient method for matching the high-energy collision calculations with the lower-energy particle showers could be used with the new model. This new method was far more efficient, successfully keeping 94 percent of the generated events for analysis, compared to only about 70 percent with the older technique. This improvement means that future searches can be conducted with greater statistical power, using fewer computing resources to achieve the same level of precision.
Finally, the team applied their new understanding to real data from the ATLAS experiment, which had previously searched for these semi-visible jets using the older model. By re-analyzing the data with both the old and new models, they confirmed that the current experimental results do not yet rule out the existence of these hidden sectors. The data showed that if such particles exist, their interactions must be weaker than a certain threshold, but the search is far from over. The study concluded that the newer, single-mediator model is a robust and reliable tool for future searches. It offers a practical path forward, allowing physicists to use the most advanced simulation software without sacrificing the accuracy needed to find the faint signatures of a hidden dark world. The work provides a solid foundation for the next generation of experiments, ensuring that when the signal of dark matter finally appears, the tools to recognize it will be ready.
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