LUXE Experiment Probes New Physics with Realistic Search for Spin-0 Particles

The search for particles beyond the Standard Model receives a boost from innovative experiments like LUXE, which is now being adapted to explore new physics through a concept called NPOD, or “New Physics search with Dump”. Melissa Almanza Soto from the Karlsruhe Institute of Technology, Oleksandr Borysov from the Weizmann Institute of Science, and Torben Ferber, also from KIT, alongside their colleagues, present a detailed analysis of how LUXE can effectively search for new, weakly interacting particles with masses below the GeV scale. Their work moves beyond earlier, simplified estimations by modelling the complete experimental apparatus, including the existing detector, to provide a realistic assessment of LUXE’s potential. The team demonstrates that this approach maintains the promise of a background-free search, significantly enhancing the experiment’s ability to uncover subtle signals of physics beyond our current understanding.

Beam Dump Backgrounds and ALP Searches

This research details studies for the LUXE experiment, which aims to discover new physics, particularly axion-like particles (ALPs), by minimizing unwanted background events. A beam dump, used to absorb leftover particles from a primary interaction, inevitably creates secondary particles like photons and neutrons that can interfere with the search. Researchers investigated various dump configurations to reduce this background noise, exploring different materials, adjusting the dump’s length and surrounding decay volume, and investigating wrapping the dump with magnetized iron to deflect charged particles and reduce neutron production. Simulations modeled the creation and transport of photons and neutrons, varying dump length and magnetic field strength. The results showed that adding a magnetic field did not significantly reduce background photons or neutrons, and even with a strong magnetic field and a longer dump, a substantial number of neutrons still reached the detector. Consequently, the authors concluded that a magnetized dump configuration offered no significant advantage for background reduction and selected a tungsten-lead configuration for the initial phase of the LUXE experiment.

Weakly Interacting Particle Search via Beam Dumps

Researchers are employing a novel technique to search for new, weakly interacting particles by repurposing an existing experimental setup as a “beam dump”. This involves directing a high-intensity photon beam onto a target, allowing any produced particles to decay over a short distance before being detected. A crucial aspect of this work is the detailed simulation of “showers” of secondary particles created when photons interact within the detector. The team developed algorithms to separate these showers, even when they occur close together, by connecting nearby energy deposits and reconstructing the paths of the original photons, allowing for precise measurement of their energy and direction. To further refine the analysis, the team implemented a boosted decision tree classifier, a powerful machine learning technique, to identify and reject background contamination from particles like neutrons, pions, and protons, analyzing shower characteristics such as shape, size, and energy distribution. The combination of detailed simulation, advanced clustering, and machine learning represents a significant advancement in the search for weakly interacting particles.

ALPs Searched For Using High-Energy Photons

The LUXE experiment, designed to investigate strong-field quantum electrodynamics, offers a unique opportunity to search for axion-like particles (ALPs), hypothetical particles that could explain dark matter and other unexplained phenomena. Researchers are using a “beam dump” approach, directing a high-energy photon beam onto a dense material to potentially create these particles. The experiment generates an intense photon beam using high-energy electrons and lasers, which interacts with the beam dump material, providing the conditions necessary for ALP production through a process known as the Primakoff effect. The key to the search lies in detecting the decay products of these ALPs, which would appear as pairs of photons, within a dedicated detector system. Researchers meticulously simulated the entire process, from photon generation to particle detection, to optimize the experiment’s sensitivity, carefully optimizing the beam dump’s design, including its length, radius, and composition, to maximize ALP production while minimizing background noise. Simulations demonstrate that a carefully designed dump, potentially incorporating a strong magnetic field, can significantly enhance the experiment’s ability to detect these elusive particles, confirming the experiment’s potential and indicating that LUXE-NPOD can explore a previously inaccessible region of parameter space for ALPs.

Background-Free Search for New Spin-0 Particles

This research details a study of the potential for discovering new spin-0 particles using the LUXE experiment as a photon beam dump. Researchers systematically investigated the experimental setup, including the beam dump design and detector performance, to determine the sensitivity to these particles. The results demonstrate that a background-free search is achievable, particularly with an optimized dump design consisting of a tungsten core and lead outer layer, combined with the silicon-tungsten ECAL detector. The study confirms earlier estimations of a background-free operation while relying on a more realistic experimental basis.

The detector’s performance, including its timing and position resolutions, allows for effective background suppression and accurate reconstruction of potential signal parameters, such as mass and coupling constant. The team optimized the decay volume length and detector size to maximize sensitivity within the parameter space LUXE-NPOD aims to probe. Future work will likely focus on refining these algorithms and exploring the full potential of the LUXE experiment for discovering new physics beyond the Standard Model, providing a strong foundation for the upcoming LUXE-NPOD search and highlighting the experiment’s unique capabilities in this area.