madminer 0.1.0

Mining gold from MadGraph to improve limit setting in particle physics.

MadMiner

Johann Brehmer, Felix Kling, and Kyle Cranmer

Mining gold from MadGraph to improve limit setting in particle physics.

Note that this is an early development version. Do not expect anything to be stable. If you have any questions, please contact us at [e-mail].

Introduction

Particle physics processes are usually modelled with complex Monte-Carlo simulations of the hard process, parton shower, and detector interactions. These simulators typically do not admit a tractable likelihood function: given a (potentially high-dimensional) set of observables, it is usually not possible to calculate the probability of these observables for some model parameters. Particle physicisists usually tackle this problem of "likelihood-free inference" by hand-picking a few "good" observables or summary statistics and filling histograms of them. But this conventional approach discards the information in all other observables and often does not scale well to high-dimensional problems.

In the three publications "Constraining Effective Field Theories With Machine Learning", "A Guide to Constraining Effective Field Theories With Machine Learning", and "Mining gold from implicit models to improve likelihood-free inference", a new approach has been developed. In a nut shell, additional information is extracted from the simulators. This "augmented data" can be used to train neural networks to efficiently approximate arbitrary likelihood ratios. We playfully call this process "mining gold" from the simulator, since this information may be hard to get, but turns out to be very valuable for inference.

But the gold does not have to be hard to mine. This package automates these inference strategies. It wraps around the simulators MadGraph and Pythia, with different options for the detector simulation. All steps in the analysis chain from the simulation to the extraction of the augmented data, their processing, and the training and evaluation of the neural estimators are implemented.

Getting started

Simulator dependencies

Make sure the following tools are installed and running:

• MadGraph (we've tested our setup with MG5_aMC v2.6.2 and have received reports about issues with newer versions)
• Pythia8 and the MG-Pythia interface installed from the MadGraph interface.
• The MadGraph-Pythia interface has issues with the treatment of multiple weights. Until this is fixed in the official release, the user has to install a patch manually. These files are available upon request.

For the detector simulation part, there are different options. For simple parton-level analyses, we provide a bare-bones option to calculate truth-level observables which do not require any additional packages.

We have also implemented a fast detector simulation based on Delphes with a flexible framework to calculate observables. Using this adds another requirement:

• Delphes, for instance installed from the MadGraph interface. Delphes has issues with the treatment of multiple weights. Until this is fixed in the official releases, the user has to install a patch manually. These files are also available upon request.

Finally, Delphes can be replaced with another detector simulation, for instance a full detector simulation based with Geant4. In this case, the user has to implement code that runs the detector simulation, calculates the observables, and stores the observables and weights in the HDF5 file. The DelphesProcessor and LHEProcessor classes might provide some guidance for this.

We're currently working on a reference Docker image that has all these dependencies and the needed patches installed.

Install MadMiner

To install the MadMiner package with all its Python dependencies, run pip install madminer.

To get the examples, including the tutorials, and the documentation, clone this repository.

Using MadMiner

Tutorials

In tutorial_1.ipynb we provide a detailed tutorial that goes through the main steps of a detector-level analysis.

After that, we recommend going through tutorial_2.ipynb, which explains local score methods, how to estimate the Fisher information, and introduces some convenient ensemble methods.

Finally, tutorial_parton.ipynb explains how to perform a parton-level Fisher information analysis.

Package structure

• madminer.core contains the functions to set up the process, parameter space, morphing, and to steer MadGraph and Pythia.
• madminer.delphes and madminer.lhe contain two example implementations of a detector simulation and observable calculation. This part can easily be swapped out depending on the use case.
• In madminer.sampling, train and test samples for the machine learning part are generated and augmented with the joint score and joint ratio.
• madminer.ml contains an implementation of the machine learning part. The user can train and evaluate estimators for the likelihood ratio or score.
• Finally, madminer.fisherinformation contains functions to calculate the Fisher information, both on parton level or detector level, in the full process, individual observables, or the total cross section.

Documentation

In docs we provide a HTML and PDF documentation of the different modules and classes.

Acknowledgements

The SCANDAL inference method is based on Masked Autoregressive Flows, and its implementation is a pyTorch port of the original code by George Papamakarios et al. available at https://github.com/gpapamak/maf.

The setup.py was adapted from https://github.com/kennethreitz/setup.py.

References

There are two main references for these inference methods applied to problems in particle physics:

@article{Brehmer:2018kdj,
      author         = "Brehmer, Johann and Cranmer, Kyle and Louppe, Gilles and
                        Pavez, Juan",
      title          = "{Constraining Effective Field Theories with Machine
                        Learning}",
      journal        = "Phys. Rev. Lett.",
      volume         = "121",
      year           = "2018",
      number         = "11",
      pages          = "111801",
      doi            = "10.1103/PhysRevLett.121.111801",
      eprint         = "1805.00013",
      archivePrefix  = "arXiv",
      primaryClass   = "hep-ph",
}

@article{Brehmer:2018eca,
      author         = "Brehmer, Johann and Cranmer, Kyle and Louppe, Gilles and
                        Pavez, Juan",
      title          = "{A Guide to Constraining Effective Field Theories with
                        Machine Learning}",
      journal        = "Phys. Rev.",
      volume         = "D98",
      year           = "2018",
      number         = "5",
      pages          = "052004",
      doi            = "10.1103/PhysRevD.98.052004",
      eprint         = "1805.00020",
      archivePrefix  = "arXiv",
      primaryClass   = "hep-ph",
}

In addition, the inference techniques are discussed in a more abstract setting, and the SCANDAL family of methods is added in:

@article{Brehmer:2018hga,
      author         = "Brehmer, Johann and Louppe, Gilles and Pavez, Juan and
                        Cranmer, Kyle",
      title          = "{Mining gold from implicit models to improve
                        likelihood-free inference}",
      year           = "2018",
      eprint         = "1805.12244",
      archivePrefix  = "arXiv",
      primaryClass   = "stat.ML",
      SLACcitation   = "%%CITATION = ARXIV:1805.12244;%%"
}

Individual inference methods are introduced in other papers, including CARL, Masked Autoregressive Flows, and ALICE(S).