Tommaso Spadaro

A bstract: A powerful way to test models with feebly interacting particles in the MeV to GeV mass range is through proton beam-dump experiments. In this paper, we compare the current sensitivity of CERN’s NA62 experiment running in beam-dump mode with that of a hypothetical experiment using the same detectors in a future CERN ECN3 beam-dump facility. When optimising such an experiment, the geometric setup is particularly relevant for the specific new-physics scenario under study, since different production mechanisms can generate different angular distributions of new particles. We show that even the most minimalistic reconfiguration of the existing NA62 experiment’s detectors can already provide a very competitive sensitivity and collect data immediately after the beam is available.

A prototype of a timing detector based on a magnesium fluoride (MgF ₂ ) Cherenkov radiator, a cesium iodide (CsI) photocathode, and microchannel plates (MCP) has been developed and tested with particle beams. Besides the conventional semitransparent photocathode directly deposited on the MgF ₂ radiator, we tested photocathodes deposited on the MCP surface and on a metal mesh placed in front of the MCP. The latest two configurations are intended to extend the photocathode lifetime by preventing bombardment of the photoemissive material by feedback ions. For these configurations, radiators with a structured surface have been manufactured to allow Cherenkov photons to exit the radiator and reach the photocathode. The obtained time resolutions for single charged particles are 12 ps, 9 ps, and 7.6 ps for mesh-based, MCP-based, and semitransparent photocathode, correspondingly.

Dark sector models present a rich phenomenology that requires high-intensity beams and precision detectors for thorough exploration. The NA62 experiment has already published several constraints on dark sector models, leveraging proton beam dump and meson decay techniques. This proposal aims to demonstrate the NA62 detector discovery potential for dark sector candidates by using the positron-on-target technique. High-intensity secondary positron beams, reaching up to ∼ 150 GeV energy, have already been produced at the North Area extracted beam lines. If a positron beam with an intensity in the range of 2 × 10 14 positrons on target per year is delivered, the NA62 detector would be ideal for searches of dark sector particles in both visible and invisible decay channels. Additionally, positron on target collisions would enable precision measurements of key standard model observables, including a detailed scan of σ ( e + e − → π + π − ) and σ ( e + e − → μ + μ − ) at the di-pion and di-muon production threshold, with discovery potential for the True Muonium ( μ + μ − ) bound state.

The NA62 experiment at the Super Proton Synchrotron at CERN aims to measure the branching ratio of the ultra-rare channel 𝐾 + → 𝜋+ 𝜈𝜈¯ with a predicted BR = (8.6 ± 0.42) × 10^ −11. The GigaTracker, a four-layer silicon-pixel tracker, measures the momentum and direction of incoming hadron beam particles at a rate of 750 MHz. The experiment’s success relies on effectively managing pile-up, temporal matching and vertex reconstruction between beam kaons and decay pions, a challenging task due to the current combinatorial track-building approach. This research integrates machine learning best practices in the current modeling strategies applied in the NA62 experiment. In this study, we extensively evaluate different deep learning architectures for particle tracking, showing the most effective approaches. In particular, we designed and implemented three distinct strategies based on Multi-Layer Perceptron, Transformer and Graph Neural Network. All methods were evaluated using efficiency, purity and fake-track rate. The most promising ones were further assessed in an aggregation-free setup, where clustering based on ground truth information was removed to test their robustness in a real-world scenario.

The PADME experiment at the Frascati DAΦNE LINAC has performed a search for the hypothetical X17 particle, with a mass of around 17 MeV, by scanning the energy of a positron beam striking a fixed target. The X17 should be produced from the resulting e ⁺ e ⁻ annihilation. Since the expected mass of this particle is only roughly known, data sidebands cannot be clearly defined. Furthermore, the need to keep the analysis blind to potentially sizable signal contributions prevents a clear assessment even of the quality of the data sample in this search. In light of these challenges, this paper presents an innovative strategy adopted by the PADME Collaboration to perform data quality checks without disclosing the X17 sample. Moreover, the procedure designed to eventually unblind the data is described, together with the statistical approach adopted to extract the limits on the coupling between the X17 and the Standard Model.