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TPC Loopers Generator - Parameter Files

This directory contains parameter files used by the TPC Loopers event generator in ALICE O2.

Overview

The TPC Loopers generator uses pre-trained ONNX models to generate realistic looper particles based on machine learning models trained on full GEANT4 slow neutron transport simulations. The parameter files in this directory provide:

  • Example statistical distribution parameters for sampling the number of loopers per event
  • Mandatory scaling parameters for transforming the ONNX model outputs to physical values

Files Description

Statistical Sampling Parameters

The files provided in the folder are examples based on the training dataset.

gaussian_params.csv

Parameters for Gaussian distribution used to sample the number of Compton electrons per event.

Format: Four values (one per line)

  1. Mean (μ)
  2. Standard deviation (σ)
  3. Minimum value
  4. Maximum value

poisson_params.csv

Parameters for Poisson distribution used to sample the number of electron-positron pairs per event.

Format: Three values (one per line)

  1. Lambda (λ) parameter
  2. Minimum value
  3. Maximum value

Scaler Parameters

These JSON files contain the parameters for inverse transformation of the ONNX models output. They should be kept as they are unless a new version of the models is released.

ScalerComptonParams.json

Scaler parameters for Compton electron generation model.

Structure:

{
  "normal": {
    "min": [array of 5 min values for min-max normalization],
    "max": [array of 5 max values for min-max normalization]
  },
  "outlier": {
    "center": [array of 2 center values for robust scaling],
    "scale": [array of 2 scale values for robust scaling]
  }
}
  • normal: Min-max normalization parameters for standard features (Px, Py, Pz, VertexCoordinatesX, VertexCoordinatesY)
  • outlier: Robust scaler parameters (center and scale) for outlier features (VertexCoordinatesZ,time)

ScalerPairParams.json

Scaler parameters for electron-positron pair generation model.

Structure:

{
  "normal": {
    "min": [array of 8 min values for min-max normalization],
    "max": [array of 8 max values for min-max normalization]
  },
  "outlier": {
    "center": [array of 2 center values for robust scaling],
    "scale": [array of 2 scale values for robust scaling]
  }
}
  • normal: Min-max normalization parameters for standard features (Px_e, Py_e, Pz_e,Px_p, Py_p, Pz_p, VertexCoordinatesX, VertexCoordinatesY)
  • outlier: Robust scaler parameters (center and scale) for outlier features (VertexCoordinatesZ,time)

Author: M. Giacalone - September 2025