BL4S 2026 · Santa Rosa de Calamuchita, Córdoba · Instituto San Francisco de AsísComechingon mortars carved 2,000 years ago and mixed contemporary plastic debris share the same river — and the same challenge: identify without destroying.
Can a particle beam reveal the internal composition of a material?
01 — The shared problem
Our city has something unusual: in the same stretch of river, an untouchable archaeological heritage and an urgent industrial challenge coexist. Both need the same thing: to know what they are made of, without destroying them.
The Río Santa Rosa — rises in the Sierras de Comechingones (≈ 1,550 m.a.s.l.), flows 58 km to the Río Tercero Reservoir. Its flow shapes the valley, its biodiversity, and the city's identity.
Carved into living rock two thousand years ago, on the banks of the Río Santa Rosa. They are provincial archaeological heritage — no analysis may damage them. SiO₂? CaCO₃? Fe₂O₃? Without taking samples, it is currently impossible to know.
Recycling cooperatives in Córdoba receive mixed plastics. A single container of PVC contaminates the entire batch and releases HCl when melted. Without fast, non-destructive identification, recycling cannot scale.
02 — The physics
A high-energy particle passes through matter and is deflected by atomic nuclei — many times, at small angles. The average exit angle (θ₀) depends on the atomic composition of the material, not its colour or shape. Heavy atoms (chlorine, iron, lead) scatter more. Light atoms (carbon, hydrogen) scatter less.
03 — The experimental setup
We need no magnet or calorimeter. The arrangement is simple and minimalist: four position detectors aligned to measure the beam trajectory before and after the material. This type of configuration is similar to those used in educational particle physics experiments and university muon telescopes.
By comparing the entry and exit directions, we obtain the angular deflection produced by the material. That angular difference is all the information needed for the analysis.
We only need silicon trackers — standard equipment at any BL4S facility. Works with e⁻ or π at 1–7 GeV/c.
Each study is configured in a YAML file. GitHub Actions runs the Highland prediction automatically and publishes the results.
The sample remains intact. The same Comechingon mortar can be analysed without removing any fraction of rock.
04 — The team's research studies
Each team member formulated their own question, derived directly from our central proposal: what can we see in the Río Santa Rosa that no one has measured yet? Each one wrote the YAML, ran the Highland prediction, and analysed the results. The graphs are real data from results/.
05 — The BeamScan Atlas
Measuring θ₀ at 3 and 6 GeV/c, each material is fixed in the plane. Light plastics at bottom-left. Heavy minerals and metals at top-right. PVC separates from the plastic cluster due to its chlorine. The metals from Jeremías's study extend the atlas towards the most extreme zone.
Hover over the points to see more information.
06 — Discriminating power
3σ discrimination between two materials depends on how different their θ₀ values are. Similar pairs (PE/PP, PMMA/Nylon) need many more events than dissimilar pairs (PE/Fe₂O₃).
Bustillo — the chlorine in PVC gives it away. Very easy at any momentum.
Tomás — iron oxide vs pure aluminium. Factor ×1.7 in angular difference.
Arturo — quartz vs iron pigment, key for the Comechingon mortars.
Iskya — detecting modern restorations in archaeological pieces.
Maia — Comechingon clay vs modern silica brick. Ceramic authentication.
Iskya — classification of recyclable plastics in cooperatives.
Lorenzo — thickness resolution in calcite/marble at 3 GeV/c. 2D scan.
Agustina — discrimination with a thin target, validating the √x/X₀ law.
Too similar in X₀ (47.9 vs 47.4 cm) — a fundamental limit of the method.
Multiple scattering distinguishes materials by their atomic composition, not their molecular structure. PE and PP have nearly the same X₀ (47.9 vs 47.4 cm) because they are equally light. These are the limits of the method, and we know them before going to CERN.
07 — The team
"We live in a small city, but we dream big."
08 — Acknowledgements
The BeamScan proposal was born at the intersection of particle physics and the land we inhabit. There are people and institutions without whom this would not have been possible.
