---
title: README
emoji: ☁️
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colorTo: red
sdk: static
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---

# Fast calorimeter simulation

Tools and studies for fast simulation of calorimeter showers: detailed
Geant4 / DD4hep simulation, compact point-cloud representations of the showers,
and their use as input to machine-learning-based fast simulation.
This organization hosts the trained weights; the code is on
[GitHub](https://github.com/fast-sim).

<p align="center">
  <img src="https://raw.githubusercontent.com/fast-sim/.github/main/profile/step2point-shower.png" alt="One 10 GeV photon shower in the Open Data Detector: 3,604 Geant4 steps, 365 points after merging within cells, 266 points after HDBSCAN clustering" width="900">
  <br>
  <em>One photon shower as Geant4 steps and after two step2point compressions.</em>
</p>

## Publications, code and data

| Paper | Code | Data and weights |
|---|---|---|
| step2point dataset: Detailed shower simulation for data representation studies, [arXiv:2509.22340](https://arxiv.org/abs/2509.22340) ([CDS](https://cds.cern.ch/record/2948746)) | [`step2point`](https://github.com/fast-sim/step2point) | Zenodo, [doi:10.5281/zenodo.17199427](https://doi.org/10.5281/zenodo.17199427) |

Library documentation: [fast-sim.github.io/step2point](https://fast-sim.github.io/step2point/)